SCHOOL SCIENCE - NCERT

Exploration of Antarctica 3P.S. Sehra

Foundation of Acoustics 10K.M. Raju and Kailash

Astronomy in Science and in Human Culture 18S.Chandrasekhar

Social Insects-I. Ants 29P. Kachroo

Social Insects-II. Bees and Wasps 35P. Kachroo

Understanding ‘Children’s Construction of 39Biological Concepts’ and its Educational ImplicationsIla Mehrotra and Vikas Baniwal

Process of Problem Solving in Physics in the 55Context of Projectile MotionShashi Prabha

A Study of Pre-service and In-service 60Teachers’ Understanding of Electrochemical CellT.J. Vidyapati, Ram Babu Pareek and T.V.S. Prakasa Rao

Teaching Aids in Mathematics and Manual for 72their ConstructionR.P. Maurya

Science Student – Teachers’ Reflection upon 86Intellectual and Procedural Honesty onConducted PracticalsA.C. Pachaury

Water Pollution 89Pushplata Verma

SCIENCE NEWS 100

BOOK REVIEW 114

SCHOOLSCIENCE

VOL. 44 NO. 3SEPTEMBER 2006QUARTERLY JOURNALOF SCIENCE EDUCATION

CONTENTS

3EXPLORATIONOF ANTARCTICA

Exploration of Antarctica

P.S. SEHRA

Department of Agricultural MeteorologyPunjab Agricultural UniversityLudhiana

NTARCTICA is the name of a greatcontinent covered with snow andice that surrounds the South

Pole. It is the 5th largest continent andcovers about 14 million squarekilometres, an area about the size of theUnited States and Mexico combined andhas a coastline of 29,600 kms. Overcountless years, snow and ice have builtup on the land burying all but 4.5 percent of it. The ice sheet counts for about90 per cent of the world’s ice. If this wereto melt, sea level would rise at least 75metres.

Antarctica is the place where a fullyear consists of only one day and onenight, each of six months duration.Daylight at the South Pole begins on21 September and ends on 21 March.

It is the coldest and windestcontinent in the world. Lowesttemperature ever recorded on our planetis – 88.3oC which is found in the lastcontinent — Antarctica.

The Antartica mainland nurtures notrees and shelters no mammals otherthan some seaguls. It supports only a fewspecies of birds such as penguins(flightless birds), snow petrels, and polarskuas.

A

Man has done magnificent work inwresting secrets from this cold continentbut Antarctica still remains a land ofmystery.

The author, who was the first Indianto visit the South Pole, tells us afascinating story of the exploration ofAntarctica.

Antarctica is the last terra incognitaon the Earth, covered with snow and icethat surrounds the South Pole. Men’s

Reproduced with permission from ‘Indian Mountaineer’ Vol. 3 (1979).

An Emperor Penguin in Antarctica. Theemperor penguins are larger birds; anaverage bird stands about three feet talland weighs about twenty-seven kg. In theautumn a single egg is laid. The youngchicks are hatched and raised during thecold and dark antarctic winter intemperatures as low as –79oC.

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minds were haunted by the idea of a greatsouthern continent for many centuriesbefore Antarctica was discovered. Earlier,the ancient Greeks believed that a greatsouthern continent must exist in orderto balance the land masses of theNorthern Hemisphere. The name of theregion has come from the Greek“Antarktikos” which means ‘Opposite theBear’, the northern constellation i.e. the‘Opposite of the Arctic’.

Many famous voyages were made todiscover the fabled continent becausemen imagined it to be populated and tocontain great riches. It was on17 January 1773, that Captain JamesCook of the British Navy became the firstman to cross the Antarctic Circle, andbrought to an end the dream of aninhabited southern continent. In 1820Captain Nathaniel Palmer of Stonington,Connecticut, and commander ThaddeusBellingshausen, and an officer of theRussian Navy, sighted the continentnear the tip of the Antarctic Peninsula.The real proof that Antarctica was acontinent came from the adventurousvoyages of Lieutenant Charles Wilkes ofthe United States Navy, Captain Dumontd’Urville of the French Navy, and JamesClark Ross of the British Navy in 1838-41. After Wilkes, d’Urville and Rossreturned to their homelands, men lostinterest in Antarctic exploration. Fornearly 50 years only sporadicendeavours were made to learn moreabout the mysterious white continent,although sealers and whalers continuedtheir operations to the far south forhunting whales and seals.

Shortly after 1890, interest in theAntarctic revived, to continue forever,

because the scientists were thenconvinced that more must be learntabout the south polar region if we are tounderstand the world and the universebetter. Moreover, new methods ofwhaling made it possible to catch anduse Antarctic whales and seals for theprospect of riches from fur and blubberoil.

In 1901, German, Swedish, andBritish expeditions took to the field. Allhad their thrilling times. Theirexperiences proved that men could livein the Antarctic from what they couldfind there, although a diet of seal andpenguin is somewhat monotonous. In1901 Captain Falcon Scott of the RoyalNavy led the British National AntarcticExpedition (1901-1904). It could be saidto be the first expedition to Antarcticawhich had very strong scientific interest.Enough scientific information was thencollected to put Antarctic studies andresearch on a sound basis. From 1901-1912, Scottish, French, Japanese,German and Norwegian expeditions wereactrive in the area.

The climax of the heroic period camein 1911 and 1912 when the South Polewas reached. First to arrive there wasthe great Norwegian explorer, RoaldAmundsen with his four companions, on14 December 1911. On 17 January 1912,about a month after Amundsen, CaptainScott and four other Englishmen stoodon the same spot. On their return fromthe Pole, misfortune followed theirfootsteps. Captain Scott had collectedabout 13 kg of rocks for scientificinterests. This was really a triumph ofscience. A distinguished AustralianScientist, Mawson, was one of the truly


great Antarctic explorers, who, in 1911-1914, set up a camp there, at what isperhaps the windiest place in the world.Winds of over 170-320 km an hour arevery frequent there. A young BritishNaval of ficer, Lieutenant ErnestShackleton, took his first expedition tothe Antarctic in 1907. The Antarcticentered his heart never to be absentuntil his death. In one of the greatestadventures, Shackleton and his menspent over six months in tents on driftingice. He lies buried in South Georgia, thegateway to Antarctica and his grave is ashrine to all who pass that way.

The period from 1895 to 1915 hassometimes been referred to as the HeroicAge of Antarctic Exploration. The periodfollowing World War I can be thought ofas the beginning of the Mechanical Age.The urgent demands of the war speededthe development of the airplane, theaerial camera, radio and motorisedtransport and all of these devices wereintroduced into Antarctic Explorationbefore 1930. Sir Hubert Wilkin,Australian leader of the Americanfinanced Wilkins-Hearst AntarcticExpedition, made the first airplane flightin Antarctic History on 26 November,1928. In fact, it was Rear AdmiralRichard E. Byrd who proved theusefulness of the airplane in Antarcticaand brought modern machines andmethods of communiction to the area.Some expeditions dug trenches in whichbuildings were placed with the hope thatsnow would blow across the coveredtrench with minimum accumulation. Pre-fabricated buildings were commonly usedin Antarctica and for small stations,vans called Wanigans, have often been

used. Looking like house trailers on skisthey were pulled into place by trackedvehicles. Because the Wanigans can bemoved it is possible to relocate them onthe surface as snow piles up. It was notuntil the advent of the new technicaladvances, such as aircraft, radios andaerial photography, that the bulk of theAntarctic coastlines and interior werefirst crudely mapped in the late pre-WorldWar II period. Afterward, much-improvedtechnical developments furtherstimulated interest in exploring thecontinent.

The first big step toward a long-rangescientific effort was taken in 1956-57. Tocontinue the international scientificcooperation that was so important, afeature of the International Geophysicalyear (IGY), the International Council ofScientific Unions established ScientificCommittee on Antarctic Research(SCAR). The Committee develops broadprogrammes in which it identifiessubjects for investigation, establishesgoals to be achieved and describesuniform methods for collection andpresenting information. Permanentoccupation also made it desirable toregulate political relationships in theAntarctic because prior to the IGY, sevengovernments had laid claim to portionsof Antarctica while three of the claimsoverlapped one another. In 1959 anAntarctic Treaty extending for 30 yearswas signed by 12 nations then activelyexploring Antarctica. They wereArgentina, Australia, Belgium, Chile,France, Japan, New Zealand, Norway,South Africa, the Union of Soviet SocialistRepublics, the United Kingdom and theUnited States of America. The Antarctic

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Treaty was signed on 1 December, 1959and became effective on 23 June, 1961when the last ratification was received.Since 1959, Czechoslovakia, Poland,Denmark and the Netherlands have alsojoined. Provisions of the Treaty openedAntarctica to unrestricted scientificexploration in a spirit of internationalcooperation. With the advent of theTreaty of Antarctic continent developedinto a scientific laboratory of the firstorder, where extensive research is beingcontinued since the IGY.

India became involved in scientificresearch in Antarctica as a result of anagreement with the USSR for jointmeteorological exploration of the upperatmosphere. Under this agreement theauthor was the Project Scientist with theSoviet Antarctica Expedition during1971-1973 and became the first Indianever to winter over the South Pole andcircumnavigate the Antarctic continent.(A brief account of the participation inthe Expedition was published in Autumn78 issue of ‘Indian Mountaineer’).

The great bulk of knowledge aboutAntarctica has been accumulated sincethe mid 1950s. Before that informationwas acquired slowly because Antarcticais not only remote but its access is toolimited and difficult. In only a few placesdoes this continent extend north of theAntarctic Circle, an imaginary linearound the Earth at about 66o 33' SouthLatitude. Including its permanentlyattached ice shelves, Antarctica coversabout 14 million square kilometres, anarea about the size of the United Statesof America and Mexico combined. Overcountless years, snow and ice have builtup on the land burying all but 4.5 per

cent of it. It is the fifth largest continentand has the highest average elevation,about 2.5 km and is overlain by acontinental ice sheet containing about90 per cent of the world’s ice. If this icewere to melt, sea level would rise at least75 m. Antarctica has about 29,600 kmof coastline and off the shore there aremany islands which are also ice-covered.They, too, are considered to be part ofthe South Polar region usually called theAntarctic.

Surrounding the Antarctic are theconfluent portions of the Pacific, Atlanticand Indian Oceans. These waters arenotoriously the stormiest in the worldbecause there is nothing to break theforce of the persistent winds. Warmertropical waters meet with cold Antarcticwaters in a remarkably discernibleclimatic and oceanic boundary rangingto the 50th Parallel known as theAntarctic Convergence. Thiscircumpolar line which variesconsiderably with longitude butgenerally within and not more than adegree or two of latitude per yearestablishes a boundary betweensubtemperate and sub-antarctic zones.South of the convergence the waters arecharacteristically ice-laden and aboundwith subpolar acquatic life. It is a feedingregion for myriads of pelagic sea birds,the world’s largest population of seals andof whales. Sealing and whaling haveprovided Antarctica with its only eco-nomic activity, the former was conductedprincipally in the subantarctic islandsand the latter on the high seas.

Along the coast piedmont glaciers, icetongues and ice shelves discharge flat-topped icebergs into the sea. Tabular


icebergs are unique to Antarctica and insome cases may be hundreds of squarekilometres in area. Where glaciers havereceded along the periphery of thecontinent, there, occasionally occur cold,arid deserts, described as ‘dry valleys’ or‘Oases’, their total area constitutes 5,600square kilometres. Farther inland, thegentle rolling surfaces of the ice-coveredand crevassed regions, in places, reflectthe hidden topography, and the natureof the sub-ice relied is also plainlyapparent from the rugged mountains andnunataks which dominate the interiorlandscape. Seismic and gravityexploration also indicates vast low lands,some depressed below sea level beneaththe existing ice sheet. The Antarcticcontinent has a diameter of about 4,500km and is asymmetrically divided by theTransantarctic Mountains into two sub-continents, East and West Antarctica.Extensive low-quality bituminous coaloutcrops to within 320-480 km of theSouth Pole, yield plant fossils whichportray an earlier age when the land wasforested. About 640 km from the SouthPole were found some fossil remains ofprimitive fresh water amphibia andreptiles known as labyrinthodents andthecodents. A reptilian skull identified asLystrosaurus establishes the formerexistence of the great southern continentGondwanaland.

About three-quarters of Antarctica liein East Antarctica which appears to bemore contiguosly a continental mass. Thesub-surface beneath the ice is extremelyrugged except west of Victoria land whereit appears to be an extensive plain closeto sea level; the maximum elevation(more than 4,000 m) occurs slightly east

of the pole of inaccessibility. Almost alland certainly the most extensive ‘eases’occur in East Antarctica, MountMelbourne and Mount Erebus, bothactive volcanoes in the Mc-Murdo Soundregion are in the East and WestAntarctica respectively. West Antarcticawhich includes Marie Byrd Land,Ellsworth Land and the AntarcticaPeninsula is the smaller sub-divisionand generally lower in elevation. Icesoundings have shown this region to belargely an ice-covered archipelago; muchof the central area is occupied by theByrd subglacial Basin with a depth asmuch as 2,500 m below sea level. Icethickness between the ‘islands’ ranges to4,270 m with elevations 1,200-1,800 mabove seal level. Volcanic activity inhistoric times is identified with DeceptionIsland. In sharp contrast to the lushnessof sea life, the continent is virtuallylifeless and devoid of the familiarvegetational features seen on other landmasses. It is without forests, brush orgrass lands and lacks rivers, estuariesand marshes. Antarctica has no nativeland vertebrates and its fresh waterfauna consists of microscopic forms. Themajor vegetation of lichens, bryophytesand algae rarely rises over 5 cm abovethe ground. The dominant landorganisms are arthropods, mites,springtails and wingless midge. However,during the short austral summermillions of sea birds, penguins and sealsmigrate to Antarctica, competing forspace on ancestral breeding grounds andbringing to the silent continent the noiseand activity of life.

Even with the tremendous effortsince 1955 to unlock its secrets,

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Antarctica remains the least known ofthe continents. This fact alone shouldensure that explorer-scientists will begoing south for a long time. Even now,scientists are developing techniqueswhich will broaden their horizons andsuggest to their imaginations newsubjects for Antarctic research. Thereare, for example, data recordingmachines powered by radioactiveisotopes. Thus they have been usedprimarily as automatic weather stationsand some difficulties have beenencountered in getting them to operateproperly in the Antarctic environment.These problems, however, can be solvedallowing expanded use of such devices.A network of automatic stations wouldoffer the meteorologist a manifoldincrease in the number of observationsavailable for both forecasting and thestudy of climate. Similar data-recordingmachines can be used in other studies.Satellites in polar orbit offer otherpossibilities. By radios, satellites couldreceive information from automaticobservatories in Antarctica andretransmit it to laboratories and weathercentres around the world. Satellites mayalso help to solve one of the greatestproblems in Antarctic operations – lossof communications. Satellites alreadyhave their place in Antarcticmeteorology, and geophysical satellitespassing over the area have obtainedinformation unavailable to observers onthe ground. Satellites carrying differentsensing equipment appear to havenumberless uses in the Antarctic. Verylittle is known about the ice pack, thefloating belt of sea ice that surrounds thecontinent. Although satellites orbitting

a hundred or more miles up can play apart here, a closer look will also benecessary. Small submersibles carriedby an icebreaker will be undoubtedlyuseful in the Antarctic waters.

The future of the Antarctica as ascientific laboratory seems assured butits natural resources are not much. Themost easily reached are those of the sea.Since the 1890s the whales of thesouthern oceans have been hunted fortheir oil and meat. Internationalagreement, however, has failed toadequately protect the stocks, andwhaling is a declining industry —perhaps a dying one. There are, though,the vast quantities of plankton on whichmost Antarctic life is based, and theJapanese and the Soviet have beeninvestigating whether plankton can beused for human nourishment. Theabundant life of the southern seas maycontribute notably to the future ofmankind. Development of Antarctica’smineral resources is a remote event. Atpresent both the nature of theseresources and their extent areimperfectly known. Even if the mineralresources prove to be valuable, thetechniques for exploitation do not nowexist. It would be, however, unwise to saythat the necessary techniques cannot bedeveloped. The Antarctic has modestprospects for tourism and its ses havereal possibilities as a source of food butthe pursuit of scientific knowledge willlong be its main attraction. Scientificdata will remain the chief export and themen who obtain it will continue to be theprincipal inhabitants. No monetaryvalues can be placed on scientificdiscoveries but anything which expands


man’s understanding of his environmentwill help him improve his condition. In1966, Peter Scott, son of the famousCaptain Scott, visited the Antarctic andhe pointed out that half the scientificresearch now drawing the explorer-

scientitists to the area is on topics noteven guessed at in his father’s days. It ispredicted that new fields requiring polarresearch will continue to appear becausethe future of Antarctica is strongly linkedto the future of science itself.

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Foundation of Acoustics

K.M. RAJU AND KAILASH

Department of Physics, BrahmanandP.G. College, Rath, Hamirpur (U.P.)

COUSTICS is the science of sound.In the first century B.C., theRoman architect Vitruvius

explained in De architectura, his famous10-volume treatise on architecture, thatsound “moves in an endless number ofcircular rounds, like the innumerablyincreasing circular waves which appearwhen a stone is thrown into smoothwater ... but while in the case of waterthe circles move horizontally on a planesurface, the voice not only proceedshorizontally, but also ascends verticallyby regular stages”. While Vitruvius didnot understand everything sound, hewas correct about this particular point.Greek mathematician Pythagoras duringthe 6th century B.C. and Greekphilosopher Aristotle during the 4thcentury B.C. had rudimentaryknowledge of sound propagation. Thesubject has developed enormouslyduring the last four centuries. The termsound implies not only the phenomenain air responsible for the sensation ofhearing but also whatever else isgoverned by analogous physicalprinciples. Thus, disturbances withfrequencies too low (infrasound) or toohigh (ultrasound and hypersound) notto be heard by a normal person are alsoregarded as sound. In words of Keats,“Heard melodies are sweeter, but thoseunheard are even sweeter.”

A

The broad scope of acoustics as anarea of interest and endeavour can beascribed to a variety of reasons. Acousticsis one of the most important branchesderived from Physics. This is as old ashumanity itself. Over the years thedevelopment has been wonderfullycrafted to make this more an appliedtechnology. Acoustics is a multi-faceddiscipline that has progressed into anapplication and has developed into manydisciplines. Interesting feature ofAcoustics is that we live with soundaround us and each sound has adefinitive meaning. Mellifluous flow ofwater, quiet waves, chirping of birds,tuned music of insects and soundsproduced by tuned instruments wereconsidered to be acoustics. Advent oftechnology has found many facetedapplications of acoustics and this hasbeen instrumental in having variousdisciplines of acoustics namely—Architectural Acoustics, BuildingAcoustics, Environmental Acoustics,Physical Acoustics, Machinery Acoustics,Musical Acoustics, Theatrical Acoustics,Speech Acoustics, etc. Thus in thepresent days of industrialisation,acoustics in general has wide applicationto many spheres of activity. Sound maybe the means of measurement fordiagnosis for one and may also be themeans of recognition for another.Subjective nature of this energy is usefulin deriving a definitive meaning forspeech production and processing inSpeech Acoustics. Sound of varied typesas a mellifluous form of energy producedby the instruments could be well fusedto suit sound of music to make listenersget themselves tuned to life to an

11FOUNDAT IONOF ACOUSTICS

escalating beating of drums inorchestrated sound. Also, with the powerof spectra, ultrasound techniques havebeen influential in the science of humanbody in identification of foreign body togrowth of any biological matter inside thesame. With the greater emphasis onenvironmental health and safety, noise—the unwanted sound as put in the rightperspective has become a strong sourceof severe health hazard in most parts ofthe globe. Specially, developing nationslike India has had this pollutant with littleor no control. The power of ultrasound,the power of artificial neural network,acoustics emission, signal processing,developments of new treatments, newtesting a calibrating facilities are someof the latest contributions to the modernworld. New processes and newtechniques are being added to the list ofthe time-tested processes.

In general, sound radiates in wavesin all directions from a point source untilit encounters obstacles like walls orceilings. Two characteristics of thesesound waves are of particular interestto us in acoustics: intensity andfrequency. Intensity is a physicalmeasurement of a sound wave thatrelates to how loud a sound is perceivedto be. We can also measure the frequencyof a sound wave, which we perceive as

pitch. For example, on a piano, the keysto the right have a higher pitch thanthose to the left. If a sound has just onefrequency, it is called a pure tone, butmost everyday sounds like speech, music,and noise are complex sounds composedof a mix of different frequencies. Theimportance of frequency arises when asound wave encounters a surface: thesound will react differently at differentfrequencies. The sensitivity of the humanear also varies with frequency, and weare more likely to be disturbed bymedium-to-high frequency noises,especially pure tones. Think of sound asa beam, like a ray of light, passingthrough space and encountering objects.When sound strikes a surface, a numberof things can happen, including:

Transmission— The sound passesthrough the surface into the spacebeyond it, like light passing through awindow glass.

Absorption— The surface absorbs thesound like a sponge absorbs water.

Reflection— The sound strikes thesurface and changes direction like a ballbouncing off a wall.

Diffusion— The sound strikes thesurface and is scattered in manydirections, like pins being hit by abowling ball. (Figure 1). Keep in mind that

Fig 1: Sound/Surface Interaction: (a) transmission, (b) absorption,(c) reflection, (d) diffusion

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several of these actions can occursimultaneously. For instance, a soundwave can, at the same time, be bothreflected and partially absorbed by a wall.

As a result, the reflected wave willnot be as loud as the initial wave. Thefrequency of the sound also makes adifferent. Many surfaces absorb soundswith high frequencies and reflect soundswith low frequencies. The AbsorptionCoefficient (a) and NRC (noise reductioncoefficient) are used to specify the abilityof a material to absorb sound. A specialproblem that results from reflectedsound is that of discrete echoes. Mostpeople are familiar with the phenomenonof shouting into a canyon and hearingone’s voice answer a second later. Echoescan also happen in rooms, albeit morequickly. If a teacher’s voice iscontinuously echoing off the back wallof a classroom, each echo will interferewith the next word, making the lecturedifficult to understand. Echoes are alsoa common problem in gymnasiums.Another type of echo that interferes withhearing is flutter echo. When two flat,hard surfaces are parallel, a sound canrapidly bounce back and forth betweenthem and create a ringing effect. This canhappen between two walls, or a floor andceiling. Sound intensity levels and soundpressure levels can be measured indecibels (dB). In general, loud soundshave a greater dB value than soft sounds.Because the decibel scale is logarithmicrather than linear, decibles cannot beadded in the usual way. An importantacoustical measurement calledReverberation Time [RT or RT(60)] is usedto determine how quickly decays sound

in a room. Reverberation time dependson the physical volume and surfacematerials of a room. Large spaces, suchas cathedrals and gymnasiums, usuallyhave longer reverberation times andsound “lively” or sometimes “boomy”.Small rooms, such as bedrooms andrecording studios, are usually lessreverberant and sound “dry” or “dead”.The Noise Reduction (NR) of a wall (alsoexpressed in dB) between two rooms isfound by measuring what percentage ofthe sound produced in one room passesthrough the wall into the neighbouringroom (Figure 2). The NR is calculated by

Fig 2: Noise Reduction between twospaces by a dividing wall

subtracting the noise level in dB in thereceiving room from the noise level in thesource room. Speech intelligibility can beevaluated in existing rooms by usingword lists. Several tests are performedwherein one person recites words from astandard list, and listeners write downwhat they hear. The percentage of wordslisteners correctly hear is a measure ofthe room’s speech intelligibility.

Frequency

Frequency is an important factor in mostacoustical measurements. Sound occurswhen a vibrating source causes small


fluctuations in the air, and frequency isthe rate of repetition of these vibrations.Frequency is measure in hertz (Hz),where 1 Hz = 1 cycle per second. A youngperson with normal hearing can detecta wide range of frequencies from about20 to 20,000 Hz. In order to deal with sucha large spectrum, acousticianscommonly divide the frequency rangeinto sections called octave bands. Eachoctave band is identified by its centerfrequency. For the standard octavebands these center frequencies are: 63,125, 250, 500, 1000, 2000, 4000, and8000 Hz. As you can see, the ratio ofsuccessive frequencies is 2:1, just likean octave in music. This also correlateswith the sensitivity of the ear tofrequency, since a change in frequencyis more readily distinguished at lowerfrequencies than at higher ones. Forexample, the shift from 100 to 105 Hz ismore noticeable than the shift from 8000to 8005 Hz. Higher-frequency octave

bands contain a wider range offrequencies than lower-frequency octavebands, but we perceive them asapproximately equal. To obtain a moredetailed indicator of the spectrum ofsound power, measurements are oftenmade in the one-third octave frequencybands. Standard center frequencies forthe one-third octave bands are: 50, 63,80, 100, 125, 160, 200, 250, 315, 400,500, 630, 800 and 1000 Hz, etc. Note thatan octave band contains the one-thirdoctave band at the standard band centerfrequency plus the one-third octavebands on each side.

Decibels

The most common measure of a sound’slevel is Sound Pressure Level, or SPL,expressed in decibels, abbreviated dB.Decibels are not typical units like inchesor pounds in that they do not linearlyrelate to a specific quantity. Instead,

Fig 3: Suitable Reverberation Times (in seconds) for various rooms typicallyfound in educational facilities.

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decibels are based on the logarithmicratio of the sound power or intensity to areference power or intensity. Soundpower and intensity are not easy tomeasure. However, sound pressure iseasily measured with a sound levelmeter. Sound pressure may also beexpressed in dB since sound pressuresquared is proportional to sound poweror intensity. We use dB instead of theactual amplitude of the sound in unitsof pressure because its logarithmic valuerepresents the way our ears interpretsound and because the numbers aremore manageable for our calculations.Most sounds fall in the range of 0 to 140dB, which is equivalent to waves withpressures of 20 to 200,000,000micropascals (or 2 × 10–10 to 2 × 10–2 atm).To help you get a feeling for soundpressure levels (in dB), the approximateSPLs of some common sound sources aregiven in Figure 4.

A simple sound level meter combinessound pressure levels over allfrequencies to give the overall SPL in dB.More complex meters have filters thatcan measure the SPL in each octaveband or one-third octave bandseparately so we can identify the level ineach band, thus identifying thespectrum of the sound. Sound levelmeters can also “weight” the soundpressure level by adjusting the level indifferent frequencies before combiningthe levels into a weighted overall level.For example, A-weighting reduces thelevel of sounds at low frequencies tostimulate the variations in sensitivity ofthe ear to different frequencies. A-weighting slightly reduces the dBA todifferentiate them from unweighted dBlevels. Similarly, C-weighted values arelabeled dBC. C-weighting slightlyreduces the level of sounds below 50 andabove 5000 Hz, but is nearly flat inbetween, and can be used to approximatean unweighted reading on sound levelmeters that only offer A- or C-weighting.Comparing A- and C-weighted levels fora noise source can provide a roughestimate of its frequency distribution. Ifthe two levels are within 1 or 2 dB, mostof the noise is above 500 Hz. If the twolevels vary by more than a few dB, asignificant amount of the noise is in thelower frequencies. To convert unweightedoctave band sound pressure levels intoweighted A or C levels, add or subtractthe amounts noted in Figure 5 from thecorresponding frequency bands. Next,sum the octave band levels (two at a timeas explained below) to arrive at theoverall dBA or dBC value.

Source SPL (dBA)

Faintest audible sound 0

Whisper 20

Quiet residence 30

Soft stereo in residence 40

Speech range 50–70

Cafeteria 80

Pneumatic jackhammer 90

Loud crowd noise 100

Accelerating motorcycle 100

Rock concert 120

Jet enjine (22.5m away) 140

Fig. 4: Sound Pressure Levels of commonsound sources.


As mentioned earlier, calculating theSPL of two sources together is not assimple as adding their individual decibellevels. Two people speaking at 70 dBAeach are not as loud as a jet engine at140 dBA. To combine two decibel values,they must be converted back to pressuresquared, summed, and converted backto decibels. The mathematics may beapproximated by using Figure 6.

projector that generates 43 dBA. Whatwill be the total sound pressure level fromthe three noise sources? The differencebetween the first two decibel values is:34–32=2, so add 2 dB to the higher value:34+2=36 dBA. Then combine this withthe projector noise: 43–36=7, so add 1dB to the higher value: 43+1=44 dBAtotal from the three noise sources. If theSPL of the teacher’s voice is 55 dBA, whatis the signal-to-noise ratio in the room?55–44=+11 dB, which is sufficient forgood speech intelligibility. How muchlouder is the total 44 dBA than each ofthe individual noise sources? Due to theresponse of our ears, we can just noticea different of 3dB. An increase of 10 dBsounds approximately twice as loud, andan increase of 20 dB sounds about fourtimes as loud.

Reverberation Time

Over 100 years ago, a Harvard physicsprofessor named Wallace Clement Sabinedeveloped the first equation forreverberation time, which has since beennamed after him and is still used today.Reverberation time is defined as thelength of time required for sound to decay60 dB from its initial level. Sabine’ssimple formula is:

RT (60) = 0.05V / (?S?)

Octave Band Center Frequency (Hz)

31 63 125 250 500 1000 2000 4000 8000

A-weighting -40 -26 -16 -9 -3 0 +1 +1 -1

c-Weighting -2 0 0 0 0 0 0 -3

Fig. 5: Frequency Discrimination in dB for A and C weighting.

Difference Amountbetween two added todecibel values higher value

0 or 1 3

2 or 3 2

4 to 9 1

10 or more 0

Fig. 6: Decibel “Addition”

If one sound is much louder than theother, the louder sound drowns out thesofter sound, and the combined decibellevel is just the level of the louder sound.If the two sounds are equally loud, thenthe combined level is 3 dB higher. Morethan two sources can be combined, butthey must be considered two at a time.For example, an unbuilt classroom isexpected to have 34 dBA of mechanicalsystem noise, a computer that generates32 dBA of noise, and an overhead

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Where:RT(60) = reverberation time (sec)V = room volume (ft3)S = surface area (ft2)? = absorption coefficient of material(s) at given frequency? indicates the summation of S times ? for all room surfaces

To use this formula, the volume ofthe room, surface area of each materialin the room, and absorption coefficientsfor those materials must be known.Absorption coefficients are measured inspecialized laboratories, and representthe fraction of sound energy (not soundlevel-dB) the material will absorb as adecimal from 0 to 1. A commonly usedone-number rating called NRC (NoiseReduction Coefficient) is simply theaverage of the absorption coefficients at250, 500, 1000 and 2000 Hz. This simple,one-number rating can be useful forcomparing the relative absorption of twomaterials; however, examiningabsorption coefficients in each octaveband gives a better idea of theperformance of a material at variousfrequencies. Reverberation time is oftencalculated with the room unoccupied.Since people and their clothing provideadditional sound absorption, anunoccupied room is the worst-casescenario, though not an unreasonableone, since occupancy of most classroomsvaries. In a complete analysis, thiscalculation should be performed for eachoctave band, as the RT can vary widelyat different frequencies. However, for aquick estimate, the RT of a classroomcan be calculated for just one octaveband representative of speechfrequencies, such as 1000 Hz. If this RT

is acceptable, then the RT throughoutthe speech range will likely be acceptable.

Speech Intelligibility

There are many methods for measuringor predicting speech intelligibility,ranging from a simple A-weighted soundlevel to the complex SpeechTransmission Index (STI). Speechintelligibility can be predicted fromreverberation time and signal-to-noiseratio. Speech intelligibility tests can beused to measure intelligibility in existingrooms. Such tests can take many forms.Typically, a speaker reads nonsensesyllables, monosyllabic words, orsentences, and listeners record whatthey hear, or choose from a list of possiblealternatives. The percentage of test itemscorrectly heard is a measure of speechintelligibility. Standardized tests havebeen developed that outline testprocedure, selection of listeners, trainingof speakers and listeners, and so on. Alsoavailable are recordings or standardizedword lists that can be reproduced insteadof having a speaker read from a list. Thiseliminates lip reading cues andvariations in different speakers’ speechcharacteristics and speech levels. Beforebeginning actual testing, listenersshould practice taking the tests in aquiet environment until they are familiarwith the procedure and their scoresreach a stable level (Words used arerandomly chosen from a standardized listso listeners cannot simply memorize theorder of the words). If speech intelligibilityin a classroom is less than 90 per cent,acoustical treatments should beimplemented to reduce reverberationand/or improve signal-to-noise ratio.


Noise Criteria Rating

The noise level in a space can beeffectively described with a single-number rating called the noise criteria(NC) rating. The NC rating is determinedby measuring the sound pressurelevel of the noise in each octave band,plotting these levels on a graph, andthen comparing the results toestablished NC curves. The lowest NCcurve not exceeded by the plotted noisespectrum is the NC rating of the sound.On most graphs, NC curves are shownin intervals of 5 to save space, but theNC rating can be given as any wholenumber in between, not just as amultiple of 5.

Sound Level vs. Distance

We all know that sound level decreasesas the distance from a sound sourceincreases. This decrease in sound levelis quantified by the inverse square law.That is, the sound energy decrease isproportional to the square of the distanceincrease. For example, if the listeningdistance from a sound source isincreased by a factor of 2 (doubled), thedirect sound energy is decreased by afactor of 4 or 2 squared (2 times 2). Thistranslates to a 6 dB reduction in thesound intensity level and the soundpressure level of the direct sound for eachdoubling of the distance from the soundsource.

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Astronomy in Science andin Human Culture*

Jawaharlal Nehru MemorialLecture 1969

PROFESSOR S. CHANDRASEKHAR

Distinguished Service Professor ofAstrophysics, University of Chicago

T IS HARDLY necessary for me tosay how deeply sensitive I am tothe honour of giving this second

lecture in this series founded in thememory of the most illustrious name ofindependent modern India. As PanditJawaharlal Nehru has written, “Theroots of an Indian grow deep into theancient soil; and though the futurebeckons, the past holds back.”

I hope I will be forgiven if I stray for amoment from the announced topic of mylecture to recall, how forty-one years ago,I was one of thousands of students whowent to greet young Jawaharlal (as weused to call him at that time) on hisarrival to address the National Congressmeeting in Madras that year.

I recall also how the dominant feelingin all of us at that time was one of intensepride in the men amongst us and in whatthey inspired in us. Lokamanya Tilak,Mahatma Gandhi, Lala Lajpat Rai,MotiIal Nehru, Jawaharlal Nehru,Sardar Patel, Sarojini Naidu,Rabindranath Tagore, SrinivasaRamanujan – names that herald thegiants that lived amongst us in that pre-dawn era.

I

The topic I have chosen for thislecture, “Astronomy in Science and inHuman Culture,” is so large that I amafraid that what I can say on thisoccasion can at best be a collection ofincoherent thoughts. In the first part ofthe lecture’ I shall make some generalobservations on ancient Hinduastronomy, particularly with reference tothe way it relates Hindu culture to theother cultures of antiquity. I am not inany sense a student of these matters. Myknowledge is solely derived from thewritings of a distinguished historian ofscience, Professor Otto Neugebauer, whohas kindly helped me in preparing thispart of my lecture.

In the second part of the lecture Ishall say something about the particularrole of astronomy in expanding the realmof man’s curiosity about his environment.

One aspect of astronomy is certain:it is the only science for which we have acontinuous record from ancient times tothe present. As Abdul-Qasim Said ibnAhmad wrote in 1068 in a book entitled,“The Categories of Nations”: “The categoryof nations which has cultivated thesciences form an elite and as essentialpart of the creation of Allah.” And heenumerated eight nations as belongingto this class: “The Hindus, the Persians,the Chaldeans, the Hebrews, the Greeks, theRomans, the Egyptians, and the Arabs”.

Chronologically, the interactionsbetween the leading civilizations of theancient world are far more complex thanthis simple enumeration suggests. Anda study of these interactions provides uswith the most impressive testimony toman’s abiding interest in the universearound him.

* Reprinted from ‘School Science’ Vol. 7, No.1, March 1969.

19ASTRONOMY IN SCIENCEAND IN HUMAN CULTURE

We know today that Babylonianastronomy reached a scientific level onlya century or two before the beginning ofGreek astronomy in the fourth centuryB.C. The development of Hellenisticastronomy, after its early beginnings, toits last perfection by Ptolemy in 140 A.D.is largely unknown. Then about threecenturies later Indian astronomy,manifestly influenced by Greek method.,emerged. This last fact raises the questionas to the way in which this transmissionof information from Greece to India tookplace. Its answer is made particularlydifficult since it implies possible Persianintermediaries. Some centuries later, inthe ninth century, Islamic astronomyappears influenced by Hindu as well asHellenistic sources.

While the Greek astronomy rapidlybecame dominant in the eastern part ofthe Muslim world from Egypt to Persia,the methods of Hindu astronomypersisted in Western Europe even as lateas the fifteenth century, as I shallindicate later.

As far as Babylonian astronomy isconcerned, we know very little about itsearlier phases. But it appears that amathematical approach to the predictionof lunar and planetary theory was notdeveloped before the fifth century B.C.:that is to say barely prior to thecorresponding stage of development ofGreek astronomy. It is, however,generally agreed that the development ofBabylonian astronomy took placeindependently of the Greeks.

An important distinction betweenthe Babylonian and the Greek methodsis this: Babylonian methods are strictlyarithmetical in character and are not

derived from a geometrical model ofplanetary motion; the Greek methods, onthe other hand, have invariably had ageometric basis. This distinction enablesus to identify their influence in Hinduastronomy.

Let me make a few remarks on Greekastronomy as it is relevant to my furtherdiscussion.

The earliest Greek model that wasdevised to account for the appearance ofplanetary motion is that of Eudoxus inthe middle of fourth century B.C. On thismodel planetary motion was interpretedas a superposition of uniform rotationsabout certain inclined axes. In spite of,many glaring inadequacies, this modelhad a profound impact on subsequentplanetary theory. The culmination ofHellenistic astronomy is, of course,contained in Ptolemy’s “Almagest” –perhaps the greatest book onastronomy ever written; and it remainedunsurpassed and unsuperceded untilthe beginning of the modern age ofastronomy with Kepler.

Ptolemy’s modification of lunartheory is of special importance for theproblem of the transmission of Greekastronomy to India. The essentially Greekorigin of the Surya Siddhanta which isthe classical textbook of Hinduastronomy — cannot be doubted: it ismanifested in the terminology, in theunits used, and in the computationalmethods. But Hindu astronomy of theNorth does not appear to have beeninfluenced by the Ptolemic refinementsof the lunar theory; and this appears tobe true with planetary theory also. Thisfact is of importance: a study of Hinduastronomy will give us much needed

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information on the development of Greekastronomy from Hipparchus in 150 B.C.to Ptolemy in 150 A.D.

In early Hindu astronomy, assummarised by Varaha Mihira in thePancha Siddhantika, we can distinguishtwo distinct methods of approach: thetrigonometric methods best knownthrough Surya Siddhanta and thearithmetical methods of Babylonianastronomy in the astronomy of the South.The Babylonian influence has come tolight only in recent years; and I shallpresently refer to its continued activepresence in the Tamil tradition of theseventeenth and the eighteenthcenturies.

I should perhaps state explicitly herethat the fact that Hindu astronomy wasdeeply influenced by the West does notby any means exclude that it developedindependent and original methods. It isknown, for example, that in Hinduastronomy the chords of a circle werereplaced by the more convenienttrigonometric function sin a – (Rsin a).

Before I conclude with some remarkson the simultaneous existence of twodistinct astronomical traditions in IndiaI should like to illustrate my generalremarks by two specific illustrationswhich are of some interest.

In 1825 Colonel John Warren, of theEast India Company, stationed at FortSt. George, Madras, wrote a book of over500 quarto pages entitled Kala Sankalitawith a Collection of Memoirs on the VariousMethods According to Which the SouthernPart of India divided Time. In this book,Warren described how he had found acalendar maker in Pondicherry who

showed him how to compute a lunareclipse by means of shells placed on theground and from tables memorised as hestated “by means of certain artificialwords and phrases.” Warren narratesthat even though his informer did notunderstand a word of the theories ofHindu astronomy he was neverthelessendowed with a memory sufficient toarrange very distinctly his operations inhis mind and on the ground.” AndWarren’s informer illustrated hismethods by computing for him thecircumstances of the lunar eclipse of May31-June 1, 1825 with an error of + 4minutes for the beginning, –23 minutesfor the middle, and –52 minutes for theend. But it is not the degree of accuracyof his result that concerns us here; it israther the fact that a continuoustradition still survived in 1825, atradition that can be traced back to thesixth century A.D. with Varaha Mihira, tothe third century in the Roman Empireand to the Seleucid cuneiform tablets ofthe second and the third centuries.

A second instance I should like tomention is an example of the survival ofHindu astronomy in parts of the Westernworld that were remote from Hellenisticinfluences during the medieval times. ALatin manuscript has recently beenpublished which contains chronologicaland astronomical computations for year1428 for the geographical latitude ofNewminster, England. It used methodsmanifestly related to Surya Siddhanta.Obviously one has to assume Islamicintermediaries for a contact of this kindbetween England of the fifteenth centuryand Hindu astronomy.


While Surya Siddhanta manifestsGreek influence, Babylonian influencehas recently been established in thepost-Vedic and pre-Surya Siddhantaperiod. For example, in the astronomy ofthat period, the assumption of a longestday of 18 muhurtas and a shortest dayof 12 muhurtas were made. This ratio of3:2 is hardly possible for India. But it isappropriate for Mesapotamia; andpossible doubts about the Babylonianorigin of this ratio were removed whenthe same ratio was actually found inBabylonian texts. In addition, a wholegroup of other parallels betweenBabylonian and Indian astronomy havesince been established. Thus, the mostcharacteristic feature of Hindu timereckoning—the tithis—occurs inBabylonian lunar theory.

Clearly all these facts must be takeninto account in any rational attempt toevaluate the intellectual contactsbetween ancient India and the Westernworld. This problem of the foreigncontacts is by no means the only, or eventhe most important, fact that is to beascertained. One must consider theDravidic civilisations of the South on parwith the history, the language, and theliterature of the Aryan component ofIndian culture. It is, as Neugebauer hasemphasised, this dualism of Tamil andSanskrit sources that will provide for us,eventually, a deeper insight into thestructure of Indian astronomy.

In his book “Rome Beyond ImperialFrontiers.” Sir Mortimer Wheeler comesto the conclusion that “the far moreextensive contacts with South India havebeen a blessing to the archeologists” buthe adds that “these contacts had no

influence on these cultures themselves.”Hindu astronomy provides an exampleto the contrary. Exactly as it is possibleto distinguish between commercialcontacts which India had through thePunjab or through the Malabar andCoromandaI Coast, it is possible todistinguish the astronomy of the SuryaSiddhanta on the one hand and theTamil methods on the other. Thisdistinction is indeed very marked. TheSurya Siddhanta is clearly based on pre-Ptolemaic Greek methods while the Tamilmethods, in their essentially arithmeticalcharacter, manifest the influence ofBabylonian astronomy of the Selecuid –Parthian period.

One must not, of course, concludethat the Tamil methods were importeddirectly from Mesapotamia while thegeometric methods came to the North viathe Greeks and through, Persianintermediaries. And as I stated earlier,the fact that the Surya Siddhantaappears to have not been influenced bythe Ptolemaic refinements, provides animportant key to the development ofHellenistic astronomy between the timesof Hipparchus and Ptolemy.

A proper assessment of the role ofHindu science in the ancient world hasyet to be made. The problem is made moredifficult, than is necessary, by thetendency of the majority of publicationsof Indian scholars to claim priority forHindu discoveries and to deny foreigninfluence, as well as, the oppositetendency among some Europeanscholars. These tendencies on both sideshave been aggravated by the inadequatepublication of the original documents:this is indeed the most pressing need.

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Since no astronomy at an advanced levelcan exist without actual computationsof planetary and lunar ephimerides, itmust be the first task of the historian ofHindu astronomy to search for suchtexts. Such texts are indeed preservedin great numbers, though actuallywritten in very late periods. But thepublication of this material is an urgentneed in the exploration of orientalastronomy.

Let me conclude this somewhatincoherent account, bearing on theancient culture of India, by emphasisingthat its principal interest lies not in thesharing or in the apportioning of creditto one nation or another but rather inthe continuing thread of commonunderstanding that has bound the elitenations of Abul-Qasim ibn Ahmad inman’s constant quest to comprehend hisenvironment.

The pursuit of astronomy at the moresophisticated level of modern science,since the time of Galileo and Kepler, isconcerned with the same broad questionseven though that fact is often observedby the technical details of particularinvestigations.

Questions that may naturally occurto one often appear to be meaningless inthe context of current science. But withthe progress of science questions thatappear as meaningless to one generationbecome meaningful to another. It is tothis aspect of the development ofastronomy in recent times that I shouldlike to turn my attention now.

The first question that I shallconsider concerns the assumption thatis implicit in all sciences. Nature isgoverned by the same set of laws at all

places and at all times, i.e. Nature’s lawsare universal. That the validity of thisassumption must be raised andanswered in the affirmative was thesupreme inspiration which came toNewton as he saw the apple fall. Let meexplain.

Galileo had formulated theelementary laws of mechanics governingthe motions of bodies as they occur onthe earth; and the laws he formulatedwere based on his studies of the motionsof projectiles, of falling bodies, and ofpendulums. And Galileo had, of course,confirmed the Copernican doctrine byobserving the motions of the satellites ofJupiter with his telescope. But thequestion whether a set of laws could beformulated which governed equally themotions of all bodies, whether they be ofstones thrown on the earth or of planetsin their motions about the sun, did notoccur to Galileo or his contemporaries.And it was the falling apple that triggeredin Newton’s mind the following crucialtrain of thought.

All over the earth objects areattracted towards the centre of the earth.How far does this tendency go? Can itreach as far as the moon? Galileo hadalready shown that a state of uniformmotion is as natural as a state of restand that deviations from uniform motionmust imply force. If then the moon wererelieved of all forces, it would leave itscircular orbit about the earth and go offalong the instantaneous tangent to theorbit. Consequently, so argued Newton,if the motion of the moon is due to theattraction of the earth, then what theattraction really does is to draw themotion out of the tangent and into the


orbit. As Newton knew the period and thedistance of the moon, he could computehow much the moon falls away from thetangent in one second. Comparing thisresult with the speed of falling bodies,Newton found the ratio of the two speedsto be about 1 to 3600. And as the moonis sixty times farther from the centre ofthe earth than we are, Newton concludedthat the attractive force due to the earthdecreases as the square of the distance.The question then arose: If the earth canbe the centre of such an attractive force,then does a similar force reside in thesun, and is that force in turn responsiblefor the motions of the planets about thesun? Newton immediately saw that if onesupposed that the sun had an attractiveproperty similar to the earth, thenKepler’s laws of planetary motion becomeexplicable at once. On these grounds,Newton formulated his law of gravitationwith lofty grandeur. He stated:

“Every particle in the universeattracts every other particle in theuniverse with a force directly as theproduct of the masses of the two particlesand inversely as the square of theirdistance apart.” Notice that Newton wasnot content in saying that the sunattracts the planets according to his lawand that the earth also attracts theparticles in its neighbourhood in asimilar manner. Instead with sweepinggenerality, he asserted that the propertyof gravitational attraction must beshared by all matter and that his law hasuniversal validity.

During the eighteenth century, theramifications of Newton’s laws for allmanner of details of planetary motionswere investigated and explored. But

whether the validity of Newton’s lawscould be extended beyond the solarsystem was considered doubtful by many.However, in 1803 William Herschel wasable to announce from his study of closepairs of stars that in some instances thepairs represented real physical binariesrevolving in orbits about each other.Herschel’s observations furtherestablished that the apparent orbits wereellipses and that Kepler’s second law ofplanetary motion, that equal areas aredescribed in equal times, was also valid.The applicability of Newton’s laws ofgravitation to the distant stars was thusestablished. The question whether auniform set of laws could be formulatedfor all matter in the universe became atlast an established tenet of science. Andthe first great revolution in scientificthought had been accomplished.

Let me turn next to the second greatrevolution in explicit context of astronomythat was accomplished during the middleof the last century.

During the eighteenth century theidealist philosopher Bishop Berkeleyclaimed that the sun, the moon, and thestars are but so many sensations in ourmind and that it would be meaninglessto inquire, for example, as to thecomposition of the stars. And it was anoft-quoted statement of Auguste Compte,a positivist philosopher, influentialduring the early part of the nineteenthcentury, that is in the nature of thingsthat we shall never know what the starsare made of. And yet that very-questionbecame meaningful and the centre ofastronomical interest very soonafterwards. Let me tell this story verybriefly.

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You are familiar with Newton’sdemonstration of the chapter of whitelight by allowing sunlight to pass througha small round hole and letting the pencilof light so isolated fall on the face of aprism. The pencil of light was dispersedby the prism into its constituent rainbowcolours. In 1802 it occurred to an Englishphysicist, William Wollaston, tosubstitute the round hole, used byNewton and his successors to admit thelight to be examined with the prism, withan elongated crevice (or slit as we wouldnow say) 1/20th of an inch in width.Wollaston noticed that the spectrumthus formed, of light “purified” (as hestated) by the abolition of overlappingimages, was traversed by seven darklines. These Wollaston took to be thenatural boundaries of the variouscolours. Satisfied with this quasi-explanation, he allowed the subject todrop. The subject was independentlytaken up in 1814 by the great Munichoptician Fraunhofer. In the course ofexperiments of light, directed towards theperfecting of his achromatic lenses,Fraunhofer, by means of a slit and atelescope, made the surprising discoverythat the solar spectrum is crossed notby seven lines but by thousands ofobscure streaks. He counted some sixhundred and carefully mapped over threehundred of them. Nor did Fraunhoferstop there. He applied the same systemof examination to other stars; and hefound that the spectra of these stars,while they differ in details from that ofthe sun, are similar to it in that they arealso traversed by dark lines,

The explanation of these dark linesof Fraunhofer was sought widely and

earnestly. But convincing evidence as totheir true nature came only in the fall of1859 when the great German physicist‘Kirchhoff formulated his laws ofradiation. His laws in this context consistof two parts. The first part states thateach substance emits radiationscharacteristic of itself and only of itself.And the second part states that ifradiation from a higher temperaturetraverses a gas at a lower temperature,glowing with its own characteristicradiations, then in the light which istransmitted the characteristic radiationsof the glowing gas will appear as darklines in a bright background. It is clearthat in these two prepositions we havethe basis for a chemical analysis ‘of theatmospheres of the sun and the stars.By comparisons with the spectralemissions produced by terrestrialsubstances, Kirchhoff was able to identifythe presence of sodium, iron,magnesium, calcium, and a host of otherelements in the atmosphere of the sun.The question which had been consideredas meaningless only a few years earlierhad acquired meaning. The modern ageof astrophysics began with Kirchhoff andcontinues to the present. And we allknow that one of the major contributionsto our understanding of the spectra ofstars and the physics of stellaratmospheres was made in our own timesby Meghnad Saha.

Now I come to a question that manhas always put to Nature: Was there anatural beginning to the universearound us? Or to put the question moredirectly: How did it all begin? All religionsand all philosophical systems have feltthe need and the urge to answer this


question. Indeed, one may say that atheory of the universe, a theory ofcosmology, underlies all religions and allmyths. And one of the earliestcosmologies, formulated as such, occursin the Babylonian epic Enuma Elish inthe second millennium B.C. The poemopens with a description of the universeas it was in the beginning:

When a sky above had not beenmentioned

And the name of firm ground belowhad not been thought of

When only primeval Apsu, theirbegetter,

And Mummu and Ti’amat—she whogave birth to them all—

Were mingling their waters in one;

When no God whosoever hadappeared,

Had been named by name had beendetermined as to his lot,

Then were Gods formed within them.

Whether the question of the origin ofthe universe can be answered on rationalscientific grounds is not clear. It mightbe simplest to suppose that in all aspectsthe astronomical universe has alwaysbeen. Or, alternatively, following Comptewe might even say that it is in the natureof things that we shall never know howor when the universe began.Nevertheless, recent discoveries inastronomy have enabled us for the firsttime to contemplate rationally thequestion: Was there a natural beginningto the present order of the astronomicaluniverse? A related question is: If theastronomical universe did have a

beginning, then are we entitled tosuppose that the laws of Nature haveremained unchanged? The two questionsare clearly related.

Let me take the second question first.Have the laws of Nature remained thesame? Can the universality of Nature’slaws implied by Newton in hisformulation of the laws of gravitation, beextended to all time in a changinguniverse?

It is clear that over limited periods oftime the laws of Nature can be assumednot to have changed. After all, themotions of planets have been followedaccurately over the past three centuries–and less accurately over all historicaltimes – and all we know about planetarymotions has been accounted for withgreat precision with the same Newtonianlaws and with the same value for theconstant of gravitation. Moreover, thephysical properties of the Milky Waysystem have been studied over most ofits extent—and its extent is 30,000 lightyears. It can be asserted that the laws ofatomic physics have not changedmeasurably during a period of thisextent. And on the earth geological stratahave been dated for times which go backseveral hundreds of millions of years. Inparticular the dating of these strata bythe radio-active content of the mineralsthey contain assumes that the laws ofphysics have not changed over theselong periods. But if during these timesthe astronomical universe in its broadaspects has not changed appreciablythen the assumption that the laws havenot changed appreciably during thesesame periods would appear to be anatural one. The questions that I have

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formulated, to have meaning, must bepredicted on the supposition that thereis a time scale on which the universe ischanging its aspect. And if such a timescale exists, the first question is: Whatis it?

That a time scale characteristic ofthe universe at large exists was firstsuggested by the discoveries of Hubblein the early twenties. There are two partsto Hubble’s discoveries.

The first part related to what may beconsidered as the fundamental unit orconstituents of the universe. It emergedunequivocally from Hubble’s studies thatthe fundamental units are the galaxiesof which our own Milky Way system isnot an untypical one. Galaxies occur ina wide variety of shapes and forms. Themajority exhibit extraordinaryorganisation and pattern.

To fix ideas, let me say that a galaxycontains some ten billion or more stars;its dimension can be measured inthousands of light years: our own galaxyhas a radius of 30,000 light years.Further the distance between galaxies isabout 50 to 100 times their dimensions.

The second part to Hubble’sdiscovery is that beyond the immediateneighbourhood of our own Milky Waysystem, the galaxies appear to bereceding from us with a velocityincreasing linearly with the distance. Inother words, all the galaxies appear tobe running away from us as though, asEddington once said, “we were the plaguespot of the universe.” Hubble’s law thatgalaxies recede from us with a velocityproportional to the distance was deducedfrom an examination of their spectra.

Now suppose that we take Hubble’slaw literally. Then it follows that a galaxywhich is twice as far as another will bereceding with a velocity twice that of thenearer one. Accordingly, if we couldextrapolate backwards, then bothgalaxies would have been on top of us ata past epoch.

More generally, we may concludethat if Hubble’s relation is a strictmathematical one, then all the galaxiesconstituting the astronornical universeshould have been together at a commonpoint at a past calculable epoch. Whetheror not we are willing to extrapolate byHubble’s law backward in this literalfashion, it is clear that the past epochcalculated in the manner I haveindicated does provide a scale of time inwhich the universe must have changedsubstantially. Current analysis of theobservations suggests that the scale oftime so deduced is about seventythousand million years.

With the time scale established, thequestion I stated earlier can berephrased as follows: Have the laws ofNature been constant over periods aslong as say thirty or forty billion years?And, what indeed was the universe likeseventy thousand million years ago?These questions cannot be answeredwithout some underlying theory.

While there are several competingtheories that are presently beingconsidered, I shall base my remarks onthe framework provided by Einstein’sgeneral theory of relativity. This theoryappears to me the most reasonable.

This is clearly not the occasion todigress at this point and describe the


content of the theory of relativity.Suffice it to say that it is a naturalgeneralisation of Newton’s theory and amore comprehensive one. On Einstein’stheory, applied to the astronomicaluniverse in the large, it follows that ateach instant the universe can bedescribed by a scale of distance whichwe may call the radius of the universe.At a given epoch it measures the farthestdistances from which a light signal canreach us. This radius varies with thetime. Its currently estimated value is tenthousand million light years. But themost important consequence that followsfrom the theory is that this radius of theuniverse was zero at a certain calculablepast epoch some seventy thousandmillion years ago. In other words, theconclusion arrived at by a naiveextrapolation backwards of Hubble’s law,interpreted literally, is indeed a validone. That the theory predicts such asingular origin for the universe issurprising; but it has been establishedrigorously, with great generality, by ayoung English mathematician, RogerPenrose.

And finally, it is an exactconsequence of the theory that the ratioof the wavelengths of an identified linein the light of a distant galaxy to thewavelength of the same source asmeasured here and now is the same asthe ratio of the radius of the universe nowand as it was when the light was emittedby the galaxy.

During the past few years a dozen ormore objects have been discovered forwhich the ratio of the wavelengths Imentioned is about three. Precisely whathas been found is the following. In a

laboratory source hydrogen emits a linewith a wavelength that is about a thirdof the wavelength of the visible extremeviolet light. But this same line emittedby the stellar object in the remote pastand arriving here on earth now isactually observed in visible light. The factthat all the identifiable spectral lines inthese objects are shifted by a factor ofabout three, means that the radius of theuniverse at the time light left theseobjects was three times smaller and thedensity was some twenty-seven timesgreater than they are now. And a carefulanalysis of the spectrum shows thatduring this span of time at any rate thelaws of atomic physics have not changedto any measurable extent. To have beenable to see back in time when the densityof the universe was thirty times what itis now is, of course, a considerableadvance. But even this ratio is very farfrom what it would have been if we takethe relativistic picture and go furtherback in time when the radius of theuniverse was say ten thousand milliontimes smaller, not merely three times ora thousand times smaller. Does it appearthat this extrapolation is meaninglessand fanciful? But the general theory ofrelativity gives a theoretical meaning tosuch a question since a state of affairsattained by such extrapolation ispredicted as an initial state for ourpresent universe. In other words, thequestion is meaningful, and one canreasonably ask: Is there anything we canobserve now that can be considered asthe residue or the remnant of that initialsingular past? But to answer thisquestion we must take the relativisticpicture seriously and determine what it

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has to say about that remote past. Sucha determination has been made byRobert Dicke and his associates atPrinceton.

Dicke calculated that at the time theradius of the universe was 10o timessmaller, the temperature should havebeen some ten thousand milliondegrees – in other words, a veritablefireball. And as the universe expanded,radiation of this very high temperature,which would have filled the universe atthat time, would be reduced. Forexample, its temperature would havefallen to ten thousand degrees after thefirst ten million years. As the universecontinues to expand beyond this point,the radiation will cool adiabatically, i.e.in the same manner as gas in a chamberwill cool if it is suddenly expanded. AndDicke concludes that the radiation fromthe original fireball must now fill theuniverse uniformly, but that itstemperature must be very low—in fact3o Kelvin, a temperature that isattainable in the laboratory only byliquefying helium. It corresponds to

radiation at a temperature of 270o of frost.How can we detect this low temperatureradiation?

It can be shown that this radiationat 270o of frost should have its maximumobservable intensity at wavelength in theneighbourhood of 3 millimetres i.e. theradiation must be present in themicrowave region. The remarkable factis that radiation in these wavelengthshas been detected; it comes withincredible uniformity from all directions;and they have all the properties that onemight, on theoretical grounds, want toattribute to such fossil radiation from theoriginal fireball.

With these discoveries I havedescribed astronomy appears to havejustified the curiosity that man has feltabout the origin of the universe, from thebeginning of time.

As I said at the outset, man’scontemplation of the astronomicaluniverse has provided us with the onecontinuous threat that connects us withantiquity. And might I add now that ithas also inspired in him the best.

29SOCIAL INSECTS–I.ANTS

Social Insects—I. Ants*

P. KACHROO

Indian Council of Agricultural Research,New Delhi

NSECTS ARE grouped under theClass Insecta of the’ animalkingdom. More than a million

different species of insects have beendescribed and named so far. Individualsbelonging to many of these species arenumerous and are sometimes describedas ‘clouds darkening the sky’ and‘swarms carpeting the ground for miles’.Some insects are large enough to bevisible but a large majority are minuteand can hardly be seen without the helpof a magnifying glass. Notwithstandingtheir small size, the total bulk of animalmatter in their bodies added togetherwould exceed that of all the other landanimals.

Most of the insects live on land,either on the surface, or in flight in theair above it. Many live in fresh water,mostly until they reach the adult stage;some live in water even as adults.

A few species dwell along theseashore above the low-water mark. Someof the land insects are migrants andmake long flights over land and sea.

Insects differ in their food habits;some eat all types of plants, some everyanimal substance, some are selective,and yet others eat nothing at all. Mayflies

I

and some moths and caddis flies eatnothing at all and are abstainers. Woodwasps, the majority of moths, beetles,and larvae of many insects arevegetarians.

Many beetles, flies, some bugs andgrasshoppers are carnivorous, eatingboth living and dead animal food. Manyinsects, like some crickets, grasshoppersand beetles eat anything that comes intheir way (omnivorous). Most of the socialinsects (ants, bees, wasps, termites)change from one type of diet to anotherin their life history: as larvae they arecarnivorous and as adults vegetarians.

Some insects, like mosquitoes, areharmful to man, yet some like the honeybee and silkworm are useful.

Many insects make possible thecross-fertilisation of flowering plants, byvisiting the flowers in search of nectarand carrying their pollen from one bloomto another.

Some insects help nature bycleaning the earth of animal excreta, andof dead bodies. Some provide food for fishand some are used as chicken feed. Someare beautiful to look at. Some areharmful, eat our clothes, bore wood,sting, or are pests of food grains. Manythrive on human blood which they suckmercilessly. Some insects eat otherinsects.

A social insect is one which lives insociety: each society consists of the twoparents, or at least the fecundatedfemale, and their offspring, and the twogenerations live to a varying extent in

* Reprinted from ‘School Science’ Vol. 4; No.1, March 1965. (This and the next article appeared in two separate issues of ‘School Science’ in 1965. These are being reproduced together to present to the readers a comprehensive view on the topic.

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mutual co-operation in a common abodeor shelter. Thus it follows that there is alengthening of the adult or parental lifeof social insects so as to allow thisdefinitive association with the progeny.

Insect societies are based on therestriction of the reproductive functionto one fertilised female, known as thequeen. In ants, however, the queen maygive birth to supernumerary queens. Theprogeny of the queen, except for thosethat are destined to perpetuate thespecies, are sterile. The sterile formsbecome the workers, and the soldiers,are endowed with special instinctivepowers that enable them to do theirduties. The workers are destined to workfor the good of the society.

The insect society is thus the bestorganised social system, the queen beingthe mother of the colony. She lays theeggs and is the autocratic ruler of thecolony. Since duties of individuals in a colonyare fixed, there is never any internal troubleor revolt, nor are there any criminals. Butcolonies fight and rob each other just asdo nations of human beings.

These insects perform theirrespective duties without having anyprevious experience, and are guided byinstinct.

Insects living in well-knit societiesare ants, bees, wasps and termites.

Ants

Characters: Ants have two or more‘waists’ and elbowed antennae. Theyhave three forms: the males, the females,and the workers. The workers differ inform amongst themselves according totheir functions.

The adult ants differ from all otherinsects in having at least oneenlargement in the waist-like part of thebody which produces two waists, onebefore and one behind the enlargement.The two waists greatly help the ants intheir mobility.

The ant has unusual mouth parts.The main jaws (mandibles) and the restof the mouth have separate functions.In most insects when the jaws are used,the mouth is necessarily open. But inants the lower lip can be closed over theupper, completely shutting the mouth,and yet leaving the jaws free, at each side,to open or close. Thus, the ants’ jaws areused both as tools, as well as ‘hands’independently of the mouth.

The heads of ants have a relativelylarge-sized brain. The wings are absentin the workers, and are only present inthe male and female. Ants have ratherspecialised legs, having a devicecombining brush and comb at thejunction between the shin and foot of theforelegs. In the abdomen there are atleast three notable organs. Someants have stings together with a glandwhich secretes poison to be injected bythem. In others the poison is there, butthe sting is replaced by a squirt withwhich it is discharged towards theenemy. All ants have two stomachs, thefirst is just the crop and the second thestomach proper. Some food in the croppasses to the stomach through a valvein between them, to be digested by theant itself; the contents of the crop aremeant to be used by the State, for theneeds of the queen, the young, or thehungry.


The queen is the fully fertile femaleand her duty is to lay fertilised eggs forthe rests of her life. These eggs aredeposited in a pouch which iscontrolled by a valve and are fertilisedone by one.

The males and females are of aboutthe same size. The workers are smallerthan these two and vary greatly in size.They lack wings, have much larger headsand much smaller eyes. The males havesmaller heads, much larger eyes and arewinged. The queens are winged first but

wingless later, their eyes are larger thanthose of the workers, but smaller thanthose of the males.Life History: Ants live together as a socialcommunity in large numbers in nests.They live as mutually dependentmembers of a State, or the nest. Thelatter may last for ever. The nest is builtthrough common labour of some of itsinhabitants.

Preparation for founding a newcolony is initiated on a hot, midsummerday.

Fig. 1: 1. House ant (Worker); 2. Male and female ants; 3. Red ant (Worker)

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The event is heralded by the flight ofa winged female ant from an old nest.She is followed by other maiden queensand males from her and the neighbouringnests. Males and females pair either inthe air during flight or after landing. Themales die after this act. The femaledeposits the eggs in a pouch.

Soon the female loses her wings. She

may find her way to her parent nest, orto a neighbouring nest, being welcomeat both the places.

However, for founding a new colonyshe has to find a suitable place in theground. She makes a hole and enlargesit into a small chamber. Here sheremains in seclusion and startsfertilising her eggs.

Fig. 2: 1. An ant colony in a stem, the opening is at the top. 2. Ant garden in Amazon, the nest is covered with seedlings. 3. A silky nest of ants in South India.

3


The eggs hatched first give rise toants which are workers. They lay thefoundations of the nest. Now the queenis fed by her worker-daughters whopump the food into her. She lays one eggevery ten minutes till she lives (6 to 7years). Some queens are reported to havelived up to 13 years. The workerdaughters manage the entire businessof the nest: feeding, housing, nursing,and defending. They collect food for all,passing it from mouth to mouth, andthus ensure equality of rations. On someof them falls the duty of building andrepairing the nest.

The nests of different species arevariable. A nest is either dug into the soilor built with sticks, pine needles orleaves, or may be a combination of thetwo. In either case the nest is chambered.

The workers have specific duties:some build the nest and some feed thequeen and carry her eggs to specialchambers built for them. There the eggshatch into larvae. The latter are movedfrom one chamber to another as cold andhot, dry and wet days succeed eachother, so that they may have exactly theright temperature and atmosphere.Eventually they pupate and form newindividuals. For defence of the colony, astaff of porters is set at the doors, whichare closed at night, or in rain or severecold, and opened in hot weather and,normally, by day. In the winter the nestis extended deeper underground. Somespecies keep two different nests, one forthe winter and another for the summer.Once the nest is complete with itscommunity, it is a permanent fixture.

There may be more than one queenin a nest but there is no sign of jealousy

between them. When a newly fertilisedqueen finds her way into a nest, she isregarded as a welcome addition to thestaff of the breeding department, andnothing more.

An ant nest is supposed to go on forever. Some remain intact for over 80years. In the larger nests more than onequeen lives and .such nests may createsatellite nests. But when populationgrows too big for a single nest, migrationtakes place. The surplus populationmoves out with one or more queens, andestablishes itself in a new nestelsewhere. It is interesting to note thatwhen the new nest is close to the old oneand the ants remain in constant touchwith each other, the new nest becomes amere satellite town and citizenship isenjoyed in common between the two. Butwhen the new nest is established faraway, the communities soon becomeforeigners and lose the community smellby which friends are recognised.Sometimes, as in case of the fiercerspecies, they become enemies and arerepelled and killed. The antennae are theorgans through which friends and foesare known.

The ants have a long life, up to 16years or more. During this period theylearn and teach their successors. Theyreceive guests and sometimes providethem board and lodge as well. Butsometimes their permanent guests(beetles) work differently and cause theannihilation of ants. Yet when migrationoccurs, the guests and other lodgers maybe seen as a procession of camp followersaccompanying the ants on their march.

Sometimes more than one kind ofants live in the same nest. Thus, a small

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species builds its tunnels and chambersin the walls separating the much widerpassages of a larger species. Somespecies live as slaves of others. A kind ofmartial race is also known. They onlyspecialise in fighting.

Some do not feed themselves or builda nest. Some are slave hunters. Theysteal the worker pupae of another kindand when the latter grow up, they aremade to do all housework and foragingfor the nest. These ants mobilize theirstrength twice or thrice a year and issueforth to repeat their slave raids. The

queens of this type behave normallybut their eggs are brought up by theslaves.

Ants live mainly on the nectar fromflowers, the juices of seeds, fruits, fungi,etc. The ants keep nectar aphids undertheir protection. Sentries are posted todefend the aphid-cattle from all invaderswhich belong to the nest. The pathsleading to trees or shrubs on which suchaphids live are also protected. Sometimesa large tree may be divided between twonests, and each will jealously defend itsown side.

35SOCIAL INSECTS—II.BEES AND WASPS

Social Insects—II. Bees andWasps

P. KACHROO

Indian Council of Agricultural Research,New Delhi

EES LIVE in permanent communi-ties.Their body has a markedwaist. The head and thorax bear

branched feathery projections whichhelp them in collecting pollen fromflowers. These projections cannot be seenby the naked eye but this characterdistinguishes bees from wasps. Thehoney bees have three types ofindividuals: males (drones), females(queens), and sterile females (workers)(Fig. 1). It is interesting to note thatdistinction between queens and workersis caused by the different food with whichthe larvae are fed. After hatching, thebrood are fed alike for the first four days.Later, some i.e., the would-be queens arefed with richer food throughout theirgrowth. They are finally provided withcells which are larger and betterventilated.

The males are large, stingless andbigeyed. The queen is smaller than themale. It continues to fertilise her eggs forthe rest of her life which is three to fouryears. The workers are much smaller buthave larger brains. They gather pollenin basket-shaped hind thighs and alsopossess the honey making and waxsecreting organs. The egg-laying organ

B

is developed and used as a weapon(sting) in the workers. After use, it iswithdrawn; but if the bee is hastilyshaken off, the sting and other organsare torn from her and she dies.

The adult bee feeds upon the nectarof flowers. Its larvae are fed upon thepollen of flowers mixed with honey, thelatter being a substance made in thebody of the bee out of nectar gatheredfrom the blooms. The larvae of cuckoo-bees, before beginning to eat the storedhoney, devour the eggs or larvae ofanother species of bees in whose nestthey have earlier been placed!

Fig. 1. Bees: (a) worker, (b) queen, (c) drone,(d) comb – a portion of normal cells and two

large queen cells

Community Life

The permanent social community of thebees is called the hive. Here, eachindividual does its share of dutiesinvolved in the community life. However,communities of bees differ from those of

Reprinted from ‘School Science’ Vol. No. 2, June 1965

a

b

c

d

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ants in certain respects. The bees in thewild state build their home in a hollowtree. Under domestication, the hive isdesigned by man to enable him to robthe honey without killing all the bees. The‘comb’, with which the hive is furnished,built of wax prepared in the bodies of theworker-bees. Such an architecturalsymmetry is not met within the ants’nest. In each hexagonal separate tubularcell is reared a single bee from the egg tothe adult stage. Normally only one queenbee lives in a hive at a time. The hive isstored with garnered foods but the ants’nest does not usually store food. The beesfly out to gather food, but the ants walkfor the same.

A new hive is founded more or lessin the same way as that of the ants. InMay, i.e., summer, when the hivebecomes overcrowded, the communityneeds a new queen. At this time, theQueen Mother is led round the queencells by her attendant workers and sheis made to lay an egg in each cell. Thelarvae hatching from these eggs aresupplied with special food or ‘royal jelly’

Fig. 2. Honey bees: a swarm clustered on abranch

throughout their life. In about 18 daysthe first of the bees developed in a royalcell is crowned as the heir-apparent. Sheis the maiden queen. Before she leavesher royal apartment, the Queen Motherleaves the hive accompanied by a swarm(about 30,000) of faithful bees, mainlyworkers. The swarm flies for some time,then the queen alights and is wrappedin a protecting mass of bees as big as awatermelon. The bee-keeper, if he islucky, collects them in this condition ina ‘skep’ and brings them home to a newmanmade hive.

Immediately, the workers get busy inbuilding the comb. They pluck the flakesof wax from between the segments oftheir bellies, mould it in their jaws, andbuild the exact cells they need. The waxis made from the honey which theworkers carry in their crops while leavingthe mother hive. The cells are of astandard size, those in the centre are thenursery cells for the young workers,those around them are the storage cellsfor honey and pollen. Drones are housedin larger cells and the still larger cellsare the royal apartments meant for thefuture queens. Soon after the new hiveis ready the routine life begins. The eggfertilising capacity of the queen can beincreased or diminished by the amountof food given to her. In winter, she doesnot lay eggs but feeds herself on thestorage cells.

Efforts are made to collect new storesand put these into the new comb as it isbuilt. Each cell containing a larva islooked after well before it pupates; thecell is sealed up by the workers with alid of pollen and wax, the latter is eatenby the emerging bee to get out.

37SOCIAL INSECTS—II.BEES AND WASPS

Ventilation in the hive is provided by anovel method; the young workers, whohave yet not flown, steadily fan with theirwings so as to make a current of freshinflowing air. This fanning also serves toevaporate the surplus water from thehoney. The entrance is guarded byguardsman to stop intruders,particularly robbers from other hives.Some intruders which cannot be stung(such as ants) are fanned away from theentrance. The dead bees are removed byoutgoing workers and dropped at adistance. The comb is repaired with aspecial glue which is obtained fromresinous buds and twigs and secreted byworkers. This is additional work for theworkers who have also to collect nectarand pollen.

Incoming bees report to their fellowsthe discovery of any rich source of foodby a dance of triumph. The scene of thedancing bee tells others what kind offlower they must seek, and once a beehas found nectar the colour of the flowerhelps to guide her back to it.

In the old hive, soon after the swarmdeparts, interesting events take place.The young queen emerges from her celland at once dashes towards the cells inwhich her sister princesses are still inthe pupal stage. She tears open theircells and stings them to death. Howawful, yet true! Sometimes she isprevented from this murderous act by theworkers and a second princess is allowedto emerge. She leads another swarm fromthe old hive. Thus, only one queen canstay in a hive. When the princess is theonly female in the hive, she mates witha drone, returns to the hive as a feeds

queen. Till she is fertile the workers donot pay any attention to her and shefeeds herself at the comb. Before leavingthe hive for her ‘marriage’ the would-bequeen flies round and about theentrance to learn her way home.

The queen lives for three to four yearsand her end is a tragic event. As soon asit is noticed that she is no longer active,her escort ruthlessly crushes, (not sting)her to death; or she is allowed to be killedby a daughter princess. At the approachof winter another tragedy betakes thehive: there is a massacre of unwanteddrones due to shortage of food. When theyreturn to the hive hungry after theirusual short unhurried flight in thesunlight, they are denied admittance andthose still in the hive at the moment areattacked and thrown out. Drones still atlarge while the massacre is on die of coldand starvation after crawling helplesslyabout for a day or two.

Fig. 3: Wasps

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True WaspsTrue wasps are social insects living inlarge colonies and producing males andfemales and a large number of sterilefemales or workers. Their social life isseasonal since the colony lasts only fora single season. The young fertilisedfemales (queens) are the only survivorswhich live through winter. Each of thequeens builds a new nest in the spring.

The adult wasps live on plant food,mostly nectar and sweet liquids(especially ripe fruits and jams). Theyoung brood is fed mostly on insectscaptured by adults and chewed up bythem before being fed to the larvae.

The mated females, like those of theants and bees, fertilize their eggs for therest of their lives. They hibernate duringthe cold weather by hanging by the jawsto curtains or other rough surfaces insome secluded spot (often in houses orsheds, in a hole in a wooden fence or acrevice in a tree). The dormant queensawake in the late spring and startconstructing a nest alone. They try to finda hole under the roots of trees or shrubsand there begin to excavate a cavity,large enough to build the first comb oftheir nests. They do not have wax butbuild with wood pulp paper, filings ofwood shaved from any wooden surfacewith their jaws and made into paper withthe wasp’s own saliva. The combresembles in shape the bee hive only inthat the cells are hexagonal tubes, setone beside the other, and each destinedfor one egg and its development into anadult wasp. The top layer is the first tobe built. It has few cells to begin with andforms a solid hanging rod. It sustains thewhole nest when completed. Later, layers

are built below the first, each hangingfrom the one above it by similar rods andforming a platform upon which the waspscan walk with access to the open ends ofthe cells above their heads. The combwhen completed is surrounded andenclosed in a very thick envelope whichis constantly enlarged.

The queen after having built partsof the comb lays an egg in each cell andwhen the larvae hatch out, she feedsthem all on countless caterpillars, flies,and other insects which she chews upand deals out from her own tongue to herhungry brood. While the larvae grow, shegoes on completing their cells. Before theypupate, they themselves close the lid ofthe cell. Through it, they eat their way outas adult wasps. From egg-laying to emer-gence of the adult, it takes about a month.

The first eggs develop into workersand when they are strong enough theyrelieve the queen of her manual duties.She at last rests from foraging andbuilding and gives herself exclusively toegg-laying. For a month more the nestincreases and prospers and then manualcomb is built with larger cells for theproduction of male and female wasps.With this increase in population, insectfood for the brood begins to run short andit is hard for the workers to collect nectarfor themselves. Besides, as their own lifeis drawing to a close, they set about a“reign of terror; the unhatched larvae arethrown away from their cells to thebottom of the nest hole and allowed todie there. Soon winter sets in and thewhole population of the nest dies of coldand starvation. The few mated queensleft to survive start fresh nests thefollowing year.

39UNDERSTANDING ‘CHILDREN’S CON-STRUCTION OF BIOLOGICAL CONCEPTS’

Understanding ‘Children’sConstruction of BiologicalConcepts’ and ItsEducational Implications

ILA MEHROTRA

Sr. Lecturer, M.V. College of Education(University of Delhi), Geeta ColonyDelhi - 110031

VIKAS BANIWAL

M.A. (Prev.), Psychology, Departmentof Psychology, University of DelhiDelhi - 110007

OUNG children possessknowledge about biologicalphenomenon. It enables them to

make sense of what they observe aboutanimals and plants.Motoyoshi (1979)reported that a five year old girlsummarised her accumulatedexperiences with raising flowers by usingthe following analogy: “Flowers are likepeople. If flowers eat nothing (are notwatered), they will fall down of hunger. Ifthey eat too much (are watered too often),they will be taken ill. Motoyoshi (1979)has also reported an anecdotal exampleof causal attribution for an animal’sunusual physical reaction. He reportedan example of five year old children in aday care centre. These children weretaking care of a rabbit. When one daythey observed an unusual excretion, theyconcluded that it might be suffering fromdiarrhoea, as a person might suffer fromdiarrhoea. After a discussion amongst

Y

themselves they decided that the rabbitmust be given some medicine for itsdiarrhoea.

Major investigations of youngchildren’s understanding of biologicalphenomenon agree that young childrenpossess “theories” about biologicalphenomenon. The term ‘theory’ means acoherent body of knowledge that involvescausal explanatory understanding.These theories concern internalprocesses involved in individual survivaland reproduction of animals and plantsand their external behaviours andproperties relevant to these processes.Young children though are totallyignorant of physiological / behaviouralmechanisms involved. They know thatexcessive eating leads to becoming fatbut they do not know the biochemical orthe physiological processes involved. Theissue under debate here is whetheryoung children possess naïve biology, achildren’s version of endogenous biologysimilar to ethno biology or folk biologywhich is separated from biology.

The acquisition of biological conceptscan be divided as: (1) the “naïve theoryof biology” that young children havebefore schooling and (2) naïve biologyinteracts with school biology to result inintuitive biology that ordinary adults inmodern societies have.

Researchers have found that youngchildren before being taught in schoolpossess a fairly well developed body ofbiological knowledge that enables themto make reasonable predictions andexplanations regarding biologicalphenomenon.

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Many concepts that children developabout natural phenomenon derive fromtheir sensory experiences. Researchesundertaken in various countries haveidentified common features in children’sideas and developmental studies aregiving useful insights into developmentof ideas during childhood years.

Children’s understanding of theconcept of Living

Researches in children’s ideas of livinghave been carried out since 1920. Thepioneering studies on children’s ideas ofliving have been carried by Piaget whoobserved that children tend to regardmany inanimate objects as capable ofsensations, emotions and intentions.This was called as ‘animism’ by Piaget.Carey suggests that progression in theconcept of living is linked to child’sdeveloping conceptual framework aboutbiological processes. Young children (4-7 years) have little biological knowledge.By the age of 9-10 years, there is amarked increase in the knowledge ofbiology. Younger children explain bodilyfunctions of living things and the activityof inanimate objects using a naïvepsychology of human behaviour ratherthan the concepts of biological function.The naïve psychology is characterised byintentional causal reasoning in thechild’s explanations, for example, ‘thesun shines in order to keep us warm’.As the biological function develops apartfrom human intentional causality, theanimistic reasoning declines.

Some researches (e.g., Bullock,1985; Massey and Gelman, 1988) haverevealed that young children can

distinguish animals and non livingthings in terms of ability to make selfinitiating movements.

Researches have also found thatchildren use personification to identifyliving objects. Personification meansusing person analogy. Young childrenare familiar with humans and use theirknowledge about humans to analogicallyattribute characteristics to less familiaranimate objects. Vasniodou (1989) hasreported that children tend to apply ananalogy on the basis of salient similaritybetween the target (object to be identified)and the source. The closer the targetobject is biologically to a human being,the more often children recognise itssimilarity and thus apply the personanalogy.

Some students have found thatyoung children attribute humancharacteristics to targets in proportionto the extent that they are perceived tobe similar to people (Carey, 1985; lnagakiand Sugiyama, 1988).

The authors of this paper hadundertaken an action research in aprimary school run by the Governmentof Delhi. It is located on the outskirts ofDelhi. The research question was ‘Howdo primary school children constructbiology concepts?’ The aspect of biologytaken up to understand this was that ofliving and non living objects. The classeschosen were from I-V. Only one sectionof each class was taken up. Photographsof six living and six non living objectswere shown to the students. They wereasked to mark the objects that theyconsider as living. The students ofclasses III-V were interviewed on the


responses they had given. The next twoportions of this paper are based on (1)the data collected and its analysis and(2) its educational implications.

Method

Photographs of six living and six nonliving objects were shown to the studentsof classes I–V. The photographs ‘are givenin Appendix I. The photographs of livingobjects shown to the students were: tree,butterfly, flower, elephant, dog and eagle.The photographs of non living objectsshown were that of sun, teddy bear, radio,clouds, train and kite. A total of 54students were taken up for study. Thenumber of students taken up is adelimitation of the study. The socio-economic status of the students takenup for the study was similar. They allbelonged to the lower socio-economicbackground. Random selectionprocedures were used to select studentsfor the present study. The classwisedistribution of students taken up for thestudy is given in Table 1.

Table 1: Number of students taken ineach class

Class No. of Students

I 3II 10

III 12IV 21V 8

Total 54

Out of the 54 students taken up forthe study, 34 were interviewed in detailregarding the answers given by them.This was the other limitation. Thestudents were asked to give the reasonsfor why they considered a photographshown as that of a living object. The datawas collected in February 2006.

Data Interpretation

The data collected was tabulated classwise for percentage responses. Thepercentage responses show thepercentage of students who haveconsidered an object living. This data was

Table 2: Shows the percentage responses of students regarding the picture beingconsidered as that of a living object.

Cla- Sun Teddy Tree Radio Clo- Butter Ele- Train Flow- Dog Kite Eaglesses Bear uds -fly phant -er

1 2 3 4 5 6 7 8 9 10 11 12 13

I 100 66.6 0 100 66.6 0 100 100 0 100 100 0

II 80.0 40.0 30.0 70.0 80.0 10.0 90.0 60.0 20.0 100 40.0 10.0

III 58.0 25.0 33.3 41.7 50.0 0 100 41.7 33.3 100 16.6 8.3

IV 71.4 14.2 14.2 38.0 57.1 4.7 100 38.0 17.2 100 28.6 0

V 75.0 37.5 12.5 75.0 62.5 12.5 100 37.5 37.5 100 37.5 12.5

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then analysed for classwise trends ifany. The data was also analysed forchanges, if any, in conceptualunderstanding across classes I to V. Theresponses given in interviews weresimilarly analysed class wise and acrossclasses I to V. The responses wereanalysed to see the accuracy ofresponses as well as the correctness ofthe reasons attributed for calling anobject living.

Classwise Analysis of PercentageResponses

The delimitation of this study especiallythe less number of students at the classI and class V level is a big hindrance ingeneralising the results at every level. Yetan effort has been made to remainobjective.

The percentage of studentsconsidering an object as living or non-living can be analysed classwise to seewhether any trend emerges. In thissection, classwise analysis of percentageresponses of an object being consideredliving has been taken up.

Figure 1: Histogram showing percentageresponses of students considering sun as

living.

By looking at Table 2, column 2 andFigure 1, it can be seen that thepercentage of students considering sunas living comes down steadily from classI to class III and then increases from classI to class V. There is no consistent patternof the percentage going down from classI to class V. But a broad conclusion canbe drawn that with the exception of ClassIII, the percentage of studentsconsidering an object as living is fairlyhigh in classes I to V.

Figure 2: Histogram showing percentageresponses of students considering Teddy

bear as living.

Table 2, column 3 and Figure 2clearly indicate that though thepercentage of students consideringTeddy bear as living has gone down fromclass I to class V, no trend has emerged.The percentage of students consideringTeddy bear as living is the least amongstthe class IV students.

Referring to Table 2, column 5 andFigure 3, it can be clearly seen that thepercentage of students considering radioas living goes down from class I to classV. No particular trend though hasemerged. The least percentage of

Per

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of s

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100% 80% 85% 71.4% 75%

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1 2 3 4 5

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66.6% 40% 25% 14.2% 37.5%0

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students considering radio as living isin class IV where only 38% studentshave considered radio as living.

Figure 4: Histogram showing percentageresponses of students considering clouds as living

From Table 2, column 6 and Figure4, it emerges clearly that the percentageof students considering clouds as livingdecreases from class I to class V. Thereis a marginal increase in percentage inclass IV and class V. In class III only halfof those who were part of the studyconsidered clouds as living. There, ofcourse, is no trend that has emerged.

Figure 5: Histogram showing percentageresponses of students considering train as living

From Table 2, column 9 and Figure5, it emerges clearly that the percentageof students who consider train as livinggoes down steadily from class I to classV. In class V, only about one thirdstudents consider train as living. Here atrend has clearly emerged.

Figure 6: Histogram showing percentageresponses of students considering kite as living

It can be seen from Table 2 column12 and Figure 6 that all students of classI consider kite as living. The leastpercentage of students who consider kiteas living is in class III.

Figure 3: Histogram showing percentageresponses of students considering radio as

living

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44SCHOOLSCIENCE

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Figure 7: Histogram showing percentageresponses of students considering tree as living

Taking up Table 2, column 4 andFigure 7, it can be seen that none of thestudents of class I have considered treeas living. The percentage of studentsconsidering tree as living increases inclasses II and III but comes down againin classes IV and V.

Figure 8: Histogram showing percentageresponses of students considering butterfly

as living

None of the students in classes I andIII have considered butterfly as living. Forrest of the classes II, IV and V no patternhas emerged. The percentage of studentsconsidering butterfly as living is though

the greatest in class V. This can be seenfrom Table 2, column 7 and Figure 8.

Figure 9: Histogram showing percentageresponses of students considering elephant

as living

Table 2, column 8 and Figure 9 showthat except for class II where 90%students have considered elephant asliving, all students (100%) of otherclasses have considered elephant asliving.

Figure 10: Histogram showing percentageresponses of students considering flower as

living

From Table 2, column 10 and Figure10, it becomes clear that none of the classI students considers flower as living. No

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trend has emerged from classes II to V.The least percentage of studentsconsidering flower as living is in class IVand the maximum percentage is inclass V.

Figure 11: Histogram showing percentageresponses of students considering dog as living

It can be clearly seen from Table 2,column 11 and Figure 11 that allstudents of all classes have considereddog as living.

Figure 12: Histogram showing percentageresponses of students considering eagle as

living

Eagle has not been considered livingby class I and class IV students as is

evident from Table 2, column 13 andFigure 12. The maximum percentage ofstudents considering eagle as living isin class V.

From the above classwise analysis ofpercentage responses it becomes clearthat no particular trends have emergedbut on the whole the following broadconclusions can be drawn:● The percentage of students

considering non living objects asliving decreases from class I to classV although no trend can beestablished. Only in the case oftrain a trend of increasingpercentages can be seen.

● The percentage of studentsconsidering living objects as livingincreases from class I class Vthough no trend could beestablished.

● Dog and elephant have beenconsidered living by almost allstudents from class I to class V.

Classwise Analysis of Interviews

Students of classes I and II could not beinterviewed. Only students of classes IIIto V could be interviewed. They wereinterviewed on why they considered aparticular object as living.

For class III. some of the responsesto the question asked have been listedbelow:

● Sun is living because it moves.(Suraj zinda hai kyunki chalta hai) -Locomotion.

● Tree is living because it moves inwind. ( Ped zinda hai kyunki hawamein hilta hai) - Locomotion.

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46SCHOOLSCIENCE

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● Clouds are living because theymove. (Badal zinda hai kyunki chaltahai ) Locomotion.

● Elephant is living because it moves.(Haathi zinda hai kyunki chalta hai)Locomotion.

● Teddy bear is not living because itdoes not move. (Gudda zinda nahihai kyunki nahi chalta) -Locomotion.

● Train moves. (Rail chalti hai) -Locomotion. Sun grows. (Suraj ugatahai) - Growth.

● Tree grows. (Ped ugata hai) - Growth.Flower grows. (Phool ugata hai) -Growth.

● Tree grows, has green leaves. ( Pedbada hota hai, hare patte rahte hai) -Growth.

From the above quoted examples itcan be seen that in class III the studentshave considered two characteristics ofgrowth and locomotion to call an objectshown as living. The characteristics havebeen taken separately and not togetherto consider an object as living. Sun istherefore considered living because “itmoves during the day”. For the samereason clouds, train and kite have beenconsidered living by many of the Class IIIstudents. Teddy bear according to somestudents is not living as it does not move.Tree and flower have been consideredliving as they grow. Growth to themmeans becoming big in size. By the samelogic some students have considered sunas living According to them the sungrows bigger during the day and henceis living. The attribute of locomotion in

living is their common observation oftheir natural surroundings. Thisobservation has been extended to thegenerality that everything that moves isliving. As an extension of this thereforesun, clouds, train and kite have beenconsidered living. The other reason ofattributing locomotion to these non livingobjects is use of erroneous language athome and later in school. Hindi is themother tongue of these students and isalso the medium of instruction in school.In Hindi, sura} ugata hai is used for sunrises. For flower and tree also the sameterm ugata hai is used. The childrentherefore erroneously consider sun asliving. Similarly, use of sura} chalta haiin common language attributes thecharacteristic of locomotion to sun. Thechildren therefore consider sun as livingin the same way as dog and elephant areconsidered living. Dog and elephant havebeen considered living as they can move.

Teddy bear has been consideredliving by some students. They haveconsidered the open eyes of teddy bearas a characteristic of living (Gudde kiaankhe khuli hai). Another student hasquoted “Teddy bear sees” (Gudda dekhraha hai). These examples show thatstudents have considered seeing as anattribute of living. They know thatanimate objects can see through theireyes. This is derived from their commoneveryday experience of watching dogs,cats and other animals that they comeacross in their lives. There are somestudents who have considered teddy bearas non living as it is a toy.

For class IV some of the responses tothe question asked are as follows:


● Eagle flies, breathes, and eats food.(Cheel udati hai, saans leti hai,khana khati hai). – Locomotion,breathing, nutrition.

● Elephant runs, breathes, and eatsfood. (Haathi bhagata hai, sans letahai, khana khata hai). – Locomotion,breathing, nutrition.

● Butterfly flies, eats food. (Titli udatihai, khana khati hai). – Locomotion,nutrition. Eagle breathes, makesnoise, and flies. (Cheel saans letihai, bolti hai, udati hai). Breathing,making noise, locomotion.

● Elephant walks, breathes. (Haathichalta hai, saans leta hai). –Locomotion, breathing.

● Flower breathes. (Phool saans letahai). – Breathing.

● Butterfly flies, breathes. (Titli udatihai, saans leti hai). – Locomotion,breathing. Tree breathes. (Pedsaans leta hai). - Breathing.

● Flower grows. (phool bada hota hai)– Growth. Tree grows. (Ped badahota hai). – Growth.

● Dog takes birth. (Kutta janam letahai). – Reproduction.

The characteristics of living taken upby students of class IV are: locomotion,breathing, nutrition, growth, andreproduction. The students haveattributed breathing and growth to bothanimals and plants. Some of thestudents have considered threecharacteristics together to term anobject as living. For example, locomotion,breathing and nutrition to term an objectas living. One of the characteristics of

making noise considered by one studentto term an object living is not consideredas a characteristic of living by biologists.Reproduction has been taken up as acharacteristic of living by one student.E.g. dog takes birth.

Many students in class IV haveconsidered sun, train, clouds, kite, teddybear and radio as living. The reasonsquoted are the same as that quoted bystudents of class III. The characteristicof locomotion has been accorded to train,clouds, kite and sun for consideringthem as living. Radio is living for somebecause ‘radio chalta hai’. Again the useof faulty language leads to erroneousconclusion of radio being a living object.

Students of Class V have taken upattributes of nutrition, death, growth andlocomotion to consider objects shown asliving. Some examples are given below:

● Eagle eats meat. (Cheel maans khatihai) - Nutrition.

● Flower gives fragrance and oncutting dies. (Phool khushboo detahai aur kata ho to marjata hai) –Death.

● Trees and plants grow in (sun) light.(Roshni se ped, paudhe badhte hai)– Growth.

● Tree grows and if its root is cut itdies. (Ped badhta hai aur agar jadkaat dein to mar jata hai) – Growthand death.

● Elephant walks and eats food.(Haathi chalta hai aur khana khaatahai) – Locomotion and nutrition.

● Tree grows. (Ped badtha hai) –Growth.

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● Flower grows and blooms. (Phoolbadhta hai, khilta hai) – Growth.

● Dog runs. (Kutta bhagta, daulta hai)– Locomotion.

● Eagle flies and eats things. (Cheeludati hai aur cheezon ko khati hai) –Locomotion and nutrition.

● Tree breaks when it dies and itsleaves dry up. (Ped marne par apneaap tut jata hai, pattiyan sookh jaatihai) – Death.

● Elephant walks and eats food.(Haathi chalta hai, khaana khaatahai) – Locomotion and nutrition.

● Elephant roars, walks and eatssugarcane. (Haathi dahata hai,chalta hai, ganne khaata hai). –Locomotion, nutrition.

● Eagle eats food just as we eat food.(Cheel hamari tarah khaana khatihai) – Nutrition.

● Butterfly flies and sucks nectarfrom flowers. (Titli udati hai, phoolonka ras choosti hai) – Locomotion andnutrition.

● Tree gets strength from water(grows) and it breathes. (Ped ko jalse taakat milti hai aur woh saans letahai) – Growth and breathing.

● Tree uses fertile soil, sun’s rays andgives fruits. (Ped upjao mitti, soorajki kirne leta hai, phal deta hai) –Nutrition.

The students of class V have beenable to specify the type of food eaten byanimals. E.g. eagle eats meat; Elephanteats sugarcane. Though thecharacteristic of death is not included

in the biological definition of living, thestudents implicitly understand thatliving objects die. This might be theircommon observation. They haveexemplified this through statementssuch as: flowers die on cutting, treebreaks up when it dies and leaves dryup. One of the causes of death cited is –if the root is cut the tree dies. This istermed as the use of vitalistic causality(Inagaki and Hatano, 1993) todifferentiate between living and nonliving. The student understands thatgrowth is associated with living and thatroots are vital for life. Cutting down ofroots therefore leads to death. It isdifferent from intentional andmechanical causality. When intentionsare attributed to a biologicalphenomenon, it is called as intentionalcausality, e.g. “we take in air because wewant to feel good”. When mechanicalexplanations are attributed to abiological phenomenon, it is called asmechanical causality, e.g. “lungs take inoxygen and give out carbon dioxide”.Another example of vitalistic causality is:the tree uses fertile soil and sunlight andgives fruits. The student here is able tounderstand the process behind theformation of fruit at least in vitalisticterms. This also helps in building a livingnon-living distinction.

Personification (person analogy) hasalso been used to term the picture of anobject shown as that of a living object.One example is: “The eagle eats food justas we eat food”.

The living - non-living distinction hasalso been made in terms of the ability tomake self initiating movements by Class


V students. An example is the statementgiven by one student: train runs byelectricity and therefore it is non living.That is, train does not make self initiatingmovements. The student has applied theexternal agent principle, which is appliedto objects which do not move on their own.

To summarise, major findings of theinterview conducted can be listed asfollows:

● Class III students have taken uplocomotion and growth ascharacteristics of living. Both thecharacteristics have been taken upseparately. Common experience hashelped the learners to differentiatecorrectly between living and nonliving. But, the use of faultylanguage at home and in the schoolhas also led learners to reach faultyconclusions about the distinctionbetween living and non living.

● Students of class IV haveconsidered locomotion, breathing,nutrition, growth and reproductionas characteristics of living. Morethan one characteristic has beentaken up by many students todistinguish between living and nonliving. The use of faulty language athome and in school has again ledto erroneous conclusions ofdistinction between living and nonliving.

● Class V students have taken upcharacteristics of nutrition, death,growth and locomotion todistinguish between living and nonliving. Besides this, vitalisticcausality, personification (personanalogy), ability to make self

initiating movements have alsobeen considered by students todifferentiate between living and nonliving. The use of faulty languagehas led again to erroneousconclusions of distinction betweenliving and non living at manyplaces.

● There are seven characteristics oflife: movement, respiration,sensitivity, growth, reproduction,excretion and nutrition asconsidered by biologists. Childrenfrom Classes I to V have consideredonly five of these sevencharacteristics to consider an objectas living. Excretion and sensitivityhave not been taken ascharacteristics by any student.

● The students were asked to givemore examples of living. These aresummarised classwise below:

I. Class III: Cat, birds, animals,crow, truck.

II. Class IV: Camel, pigeon.

Ill. Class V: Man, lion, snake,monkey, parrot,donkey, horse, cow,pigeon, aero plane, ox.

Discussion

From the findings discussed above, a fewmore broad generalisations can be drawn:

● The children in class I ( 5-6 years)do not possess an adequate livingnon living distinction. Though nogeneralisations can be drawn as thedata available is also not adequate.Plants are not considered living bythese children.

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● Some of the children in class II startrecognising plants as living

● Non-intentional causality andpersonification start developing bythe time the child reaches ten yearsof age.

It is clear from the data collected thatchildren at six years of age have acquiredsome form of biology. Biology is nottaught in classes I and II. The earlyacquisition of biology may be due to theirwide ranging interactions with theenvironment. The children may alsohave pets at home. Some form ofgardening / cultivation practices mayalso have been followed at home. Naïvebiology is thus gradually constructedthrough daily experiences during earlyyears. There are of course many innateconstraints as children seldom needbiological knowledge, since they do nothave to find food or take care of theirhealth. By innate constraints we meancognitive constraints. Acquired priorknowledge which is limited in youngchildren especially regarding biologicalphenomena, may therefore pose aninnate constraint. It is possible thatyoung children in whom biologicalknowledge is limited may borrowpsychological knowledge to interpretbiological phenomena.

Naïve biology may also be affected bycultural and linguistic constraints. Theactivity based experiences in the culturethe children are brought up incontributes to the formation of naïvebiology. For e.g. if children are activelyinvolved in raising animals, they acquirea rich body of knowledge about them.

This knowledge can then be used by themalong with the knowledge about humansas a source for analogical predictionsand explanations for other biologicalkinds. Similarly children who areinvolved in gardening/ cultivation willacquire a rich knowledge about plantsas living organisms. This knowledge canbe used by them in analogicalpredictions. This does not mean that thechildren acquire a richer knowledgeabout animals or plants in general. Theyacquire only a richer procedural, factualand conceptual knowledge about theanimal they have raised. But, in effect,this knowledge can be used to makeanalogical predictions.

The use of language also affectsthe acquisition of biology conceptsin young children. Use of languagethat erroneously provides a living statusto non living objects makes childrenreach wrong generalisations. Manyexamples have been discussed inclasswise analysis of interviews ofchildren. On the other hand, languagemany a times helps in the proper conceptformation.

Biology is a subject which is basedon complex, hierarchically organisedcategories. It relies on mechanicalcausality. As children grow older, thepersonifying and vitalistic biologygradually changes towards truly “non -psychological” biology. The developmentof category based inferences andmechanical causality takes place.Intentional causality is rejected. Afundamental restructuring of knowledgetakes place.


Educational Implications

Many conclusions regarding educationalimplications can be drawn from thisstudy:

● In school while teaching as well asin books care must be taken aboutthe linguistic aspect. For eg, the useof Suraj Chalta hai is incorrect. Thecorrect sentence for sun rises issuryodaya hota hai. Also, whilebuilding a curriculum for biologyinstruction, the culturalperspectives must be taken intoaccount. The children coming froman agricultural background willcarry with them a rich proceduralknowledge about the animals andplants that are raised on the farm.The curriculum designers can keepthis in mind while framing thecurriculum. Examples with whichchildren are familiar due to theircultural backgrounds should beincorporated in the text.

● For classroom, teaching conceptattainment (Jerome Bruner, 1956and Joyce and Weil, 1972) could befollowed where concepts are taughtusing exemplars and non-exemplars. This method can beused in classes IV and V. Oneexample is described below:

The teacher announces in the classthat “I have a category in mind. I amgoing to show you some examples thatfit into the category and I am also goingto show you some examples that do notfit into the category. What you must dois to figure out the category for thepositive examples that I show you”. She

then pastes pictures on a flannel boardas follows:Dog Yes (A smiling face with

examples enhances interestin children)

Train No

The students start their discussionas follows:

Manu says : I think we are talking aboutpet animals.

The teacher then shows:

Eagle YesKite No

Rakesh says : I think, it cannot beabout pets. It is about allanimals.

The teacher then pastes pictures asfollows:

Elephant Yes Neem Tree Yes

Teddy-bear No

It is very confusing as neem tree is a‘Yes’ says Manu.

The teacher intervenes at this pointand asks learners to identify thecommonality in the examples cited:

Mamta who was sitting perplexedsays: Ma’am they all can walk but theeagle flies.

Deepak who was very quiet till thisintervenes and says: But, neem treecannot walk. So, this can not be thecommonality.

Rakesh: But, they all grow fromsmall to big.

The teacher can use pictures hereof a pup, baby elephant, small neem-plant etc. The discussion continuesalong with more examples and non-

. .

. .

. . . .

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examples till all the characteristics ofliving are identified. At the end theteacher lists out all the characteristicsand declares that these are all examplesof living objects. The non-examples areall non-living objects. The non-livingobjects do not show the characteristicsshown by living objects. The movementof living and non-living will bedifferentiated by telling the differencebetween self-initiated movement andmovement due to external agent. Plantsdo not show movement of the same kindas of animals yet they are considered asliving can also be discussed. Theconcluding event of this conceptattainment procedure will be askinglearners to quote more examples of living.

● The stories that the children reador hear should have less of animismi.e the inanimate objects shouldnot be associated with intentions,sensations and emotions.

● Children tend to generalise thisimpression.

● Field trips to various zoological andbotanical parks can be organised tocreate awareness about the livingworld. Field trips within the schoolcampus can also be arranged. Thechildren can become familiar withplants as living beings. Theseshould be followed by classroomdiscussions.

● Educational CDs can be used to

create more awareness about theliving and the non-living world.MCD/Government Schools alsohave access to at least one/twocomputers. These computers can beused for group instructions. Theonly requirement here is a lot of pre-planning associated with groupinstructions. A follow-up to assessthe understanding of the childrencan also be organised. The studentscan be asked to give more examplesof living objects along with theircharacteristic features by whichthese objects have been termedliving.

Conclusions

Further research by taking up morenumber of students can be carried outfor better generalisation of results. Also,various misconceptions regardingconcepts as animals, plants, cell,rusting, gravitation can also form thebasis of further research. Theeducational applications derived fromsuch research will go a long way inimproving teaching methods. Also,curriculum designers will be able toincorporate corrections of language inbooks so that such misconceptions aretaken care of. Examples of conceptskeeping in mind the cultural backgroundof students can be incorporated in booksby curriculum designers.


1 2 7

3 4 8

59 10

11 6 12

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REFERENCES

OLSON, D.R AND TORRANCE, N. 1998. The Handbook of Education and HumanDevelopment. Blackwell Publishers.

EGGEN, P.D., KAUCHAK, D.P. AND HARDER, R.J. 1979. Strategies for Teachers.Prentice-Hall, Inc., Eaglewood Cliffs, New Jersey.

JOYCE, B. AND WEIL, M. 1990. Models of Teaching (3rd edition). Prentice Hall oflnda.

DRIVER, R., RUSHWORTH, P., SQUIRES, ANN. AND WOOD-ROBINSON, V. 1997. Makingsense of secondary science research into children’s ideas. Roultedge, Londonand New York.

55PROCESS OF PROBLEM SOLVING IN PHYSICSIN THE CONTEXT OF PROJECTILE MOTION

Process of Problem Solvingin Physics in the Context ofProjectile Motion

SHASHI PRABHA

Lecturer in Physics, DESM, RIE, Ajmer

HEN SOLVING the problems inPhysics, multiple ideas come tothe mind of the learners (Gandhi,

Varma, 2004) . Their cognitive thinkingmay follow these sequences –

● They try to fit the problem in theirexisting cognitive schemes.

● They try to correlate the problemwith their earlier experiences.

● They describe the problem byidentifying the given quantities andthe quantity/quantities to be foundout.

● They prepare suitable hypothesisfor solving the problem.

● They plan for action by identifyingscientific principles and formula tobe applied in the given situation.

● They analyse and/ or synthesisethe relationship between thecomponents of the problem and forma mental model of the relationshipand concept.

● They apply the principles andformula with reasoning to arrive atthe solution.

● They verify the result by going backto the problem to confirm thatsolution is correct.

W

As teaching of problem solving skillsis one of the basic aims of PhysicsInstruction (Huffman, 1997), learnersshould be empowered to reflect on theproblems independently. It becomes allthe more important in the light of the factthat solving different types of problemsrequires attacking the problems usingdifferent strategies and different steps.Teachers’ role is to guide the learners todecide

● which strategy is to be chosen;

● how it should be applied;

● why that particular strategy is beingused; and

● when that strategy is to be applied(Gandhi, Varma, 2004).

It facilitates the learners in self-exploration and recognition of a suitablestrategy. Becoming aware of their ownstrategies, they learn to orient theircognitive thinking to solve the problemby organising their thought in logicalsequence and solve the problemindependently.

Teacher has to make the process ofproblem solving transparent by exposingher own thinking patterns andsequences in dealing with the problem.She should discuss her own thinkingprocess clearly to attack the problem. Itwould serve as a model to the learners.Simultaneously she should encouragethe learners to give their ideas followedby the reasons and explanations forsuggesting those ideas. By weavingthinking patterns for different steps ofthe solution of the problem with the helpof learners, problem solving performance

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and hence conceptual networkspertaining to principles of Physics canbe strengthened. It develops cognitiveschema of the learners facilitatingconstructive learning. Also learnersbecome able to describe the problemfirst qualitatively, then quantitatively,which is a sound technique of problemsolving in Physics (Duncan, 1997). Inthis process, they evaluate theirstrengths and weaknesses related toproblem solving skills. Thus the highestlevel of learning of creative self-directiontakes place and learners can solve theproblems at their own initiative.

In this paper, an attempt is made tolook for a simplistic approach to problemsolving process in the context of projectilemotion. It is suggested to work out thesequential steps for problem solving

in teaching learning process as givenbelow.

Let us now project the process ofproblem solving in projectile motion.

Exemplar Problem – 1

A person aims at a target on the groundfrom a horizontal distance of 100 m. Ifthe gun can impart a velocity of 500ms-1 to the bullet, at what height abovethe ground must he aim his gun to hitthe target?

Solution

A. Defining Problem Situation

Draw a diagram of the situation andsimulate the situation in the classroomin order to make the learner visualise thenature the problem.

1. Draw the diagramSimulate the situation in order to correlate it withreal world problems

2. Locate the given quantitiesLocate the quantity/quantities to be found outPrepare plan of action

3. Gradual development of thought towardsattainment of solutionSeek solution

4. Reanalyze the situations of the problemSynthesize the concepts of the problemDevelop holistic approach of learning the conceptsinherited with the problemReconstruct the ideas related with the conceptsof the problem

Defining theproblem situation

Describing the problem

Thought Process

Visualisation

▲▲

▲▲

▲▲

▲


Fig. 1

C. Thought Process● Vertical distance of the projectile

from the ground can be determinedby the expression

y = ( u sin Q ) t – ( ½) gt2

● But t is not given.

● t can be calculated by using thegiven data as

t = distance/velocity = 100 m / 500ms –1 = 0.2 s

● Substituting the value of t in thisequation for y, we get

y = (0 × 0.2) + (½) × 10 × (0.2)2

= 0.2 m

= 20 cm.

● Here initial velocity is zero andacceleration due to gravity is takenas 10 ms-1.

D. Visualisation of the Problem

● Now let us write the calculatedvalue of height in the language formfor clarifying the situation of theproblem as—

The person should aim his gun at aheight 20 cm from the ground to hit thetarget.

Exemplar

Problem–2

It is possible to project a particle with agiven velocity in two possible ways so asto make it pass through a point at adistance r from the point of projection.Determine how the product of the timetaken in both ways to reach the point isrelated with r.

B. Describing of Problem

Given quantities Quantity to be found out

● Distance between the man and ● Height of the gun above the

the target on the ground = 100 m ground to hit the target?

● Velocity of the bullet = 500 ms-1

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Solution

A. Defining the Problem

Simulate the situation in the classroomby taking an object and specifying x andy coordinates with respect to it.

Draw the diagram representing thesituation.

B. Describing the Problem

As given in the box below.

C. Thought Process

● First determine the value of initialvelocity, then that of r.

● Let the time taken by the particleat point A in two different cases bet1 and t2 respectively.

● Initial velocity can be determined bythe equation of verticaldisplacement of the particle.

y = u (sinq) t - (½ ) gt2 .............(1)

● In the given situation u needs to beresolved into two rectangularcomponents as –

Component along OA = u cos (Q - β)

Component along OB = u sin (Q - β)

● Components of acceleration due togravity

along OA = - g sin B

along OB = - g cos B

Given quantities

● A particle can be projected frompoint O in two different ways butwith same velocity so as to reach ata point A. (OA = r)

● The particle reaches at A in twodifferent times.

● Since initial velocity of the particleremains same in two different cases,it is being thrown at two differentangles

Quantities to be found out

● Relation between

(t1 × t2) and r

● For this the value of r is to bedetermined

● In order to determine r, which ismeasurement of distance OA, we needto know the value of initial velocity.Hence we have to first find velocityof the particle.

Fig. 2

Here, the problem demands that we need to develop the solution backwards.


● Now displacement of the particlealong the direction perpendicular toOA is zero. Therefore substitutingthese values in equation (1), weget

0 = u sin (q - b ) t - (½) (g cos b)t2 ...........(2)

or, t = 2 u sin (q - b ) / g cos b............(3)

and u = gt cos b / 2 sin (q - b )............(4)

● To find OA = r

From the right angled triangle OCA

OA = OC/cos b = (u cos q) t /cos b

Putting the value of u from equation(4).

OA = r = (t cosq / cos b) [ gt cos b/2 sin (q - b)]

or r = (g cos q)t2 / 2 sin (q - b)...........(5)

● Now, since the particle is projectedwith the same initial velocity in thesecond case, its angle of projectionand time taken to reach upto pointA would be different.

● Let it be t1 for angle of projection q1

and t2 for angle of projection q2.

● Now r = (g cos Q1) t12 / 2 sin (Q1 - β)

also r = (g cos q2) t22 / 2 sin (Q2 - β)

● t12 t2

2 α r2

D. Visualisation of the Problem

Hence the product of the time taken bythe projectile with same initial velocitybut thrown with different angle ofprojection is directly proportion to itsdistance r from the point of projection.

Above exemplar problems aresuggestive and not prescriptive, as thethought processes vary from person toperson depending upon his experientialknowledge, interest and aptitude. Also,one person may go through differentthought processes at different time.Hence a problem may be tackled by anumber of different approaches.

For the gradual development andgrowth of the solution, reasoning patternof the thinking need to be strengthened.But it is worth mentioning that no matterhow strong is the reasoning and how wellwoven the thinking patterns of thelearner are, they must have clearconcepts of the underlying principles ofPhysics.

It is said that a problem is a problembecause there is no set steps for arrivingat the solution. Hence it is imperative forthe teacher to inculcate in the learnerthe values of self-awareness about theirthought processes thereby leading toself-exploration, self-instruction and self-evaluation.

REFERENCES

BHATNAGAR, V.P.1999. An In-depth study of Physics. Pitambar Publication, NewDelhi.

DUNCAN, T. 1997. Advanced Physics. John Murray (Publishers) Ltd., p-6.GANDHI, H. AND VARMA, M. 2004. Elucidating Mathematical Problem Solving

Through Meta-cognition. Journal of Indian Education, 30 (3), pp 71-77.HUFFMAN, D. 1997. Effects of Explicit Problem Solving Instruction on High School

Students’ Problem Solving Performance and Conceptual Understanding ofPhysics, 34(6), pp 551-570.

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A Study of Pre-service andIn-Service Teachers’Understanding ofElectrochemical Cells

T.J.VIDYAPATI

Regional Institute of Education (NCERT),Bhubaneswar

RAM BABU PAREEK

RIE, NCERT, Bhubaneswar

T.V.S. PRAKASA RAO, Vice-Principal,Jawahar Navodaya Vidyalaya, Dharwad

survey of recent literaturereveals that a good number o fresearch reports/articles

appeared in national and internationaljournals on students’ understanding ofvarious science concepts. Theresearchers have evolved different termsto describe these understandings. Driverand Easley (1978) preferred to call thempre-conceptions; Gilbert, Osborne andFensham (1982) used the term children’sscience; Cho, Kahle and Nordland (1985)evolved the term misconceptions; Driverand Erickson (1983) used the termalternative frameworks and Fischer andLipson (1986) preferred to address thesame as students’ errors. The term tobe used to reflect on students’understandings depends much on thecontext of concept development and thequantity of knowledge concerned.According to the fundamental views ofepistemology expressed by Driver (1989),Piaget (1972) , Pines and West (1986),students constructor generate theirknowledge through a set of preconcep-

A

tions based on previous knowledge andexperience and it is termed asconstructivist perspective. The net resultis that some constructions by studentsmay be erroneous and such mis-constructs adversely affect subsequentlearning of related concepts.

Electrochemistry is an importantbranch of chemistry and its knowledgeis essential to understand corrosionprinciples, electrolytic refining andelectroplating. There has been hardlyany contribution in the area ofelectrochemistry education till later partof eighties except for some studies likePfundt and Duit (1991) whichdocumented students’ misconceptions inchemical education. Finley, Stewart andYarroch (1982) have reported thatstudents find the topic of operation ofelectrochemical cells difficult. Garnettand Treagust (1992) in their articlefocused on students’ understanding ofelectric currents and the identificationand balancing of oxidation reductionequations. Sanger and Greenbowe (1997)reported common student mis-conceptions in galvanic, electrolytic andconcentration cells. Prompted by thisstudy, Sanger (2000) investigated the useof computer animations and instructionsbased on conceptual change theory tocounter students’ misconceptions inelectrochemistry. Sanger and Greenbowe(1999) analysed ten college chemistrytextbooks, identified vague, misleadingor incorrect statements in oxidation —reduction and electrochemistrychapters and came out withsuggestions concerning electrochemistryinstructions intended for teachers andtextbook writers. Ogude and Bradley

61A STUDY OF PRE-SERVICE AND IN-SERVICE TEACHERS’ UNDERSTANDING

(1994) investigated on pre-college andcollege student difficulties regardingqualitative interpretation of themicroscopic processes that take place inoperating electrochemical cells.Greenbowe (1994) studied theeffectiveness of an interactive multimediasoftware programme and reported thatthe programme helped students achievea better conceptual understanding of theprocesses occurring in electrochemicalcells.

The present study investigates theunderstanding of electrochemical cellsheld by in-service and pre-servicesecondary level science teachers andcompares their ideas with seniorsecondary level students’ under -standings of electrochemical cells. Anattempt has been made to remove certainmisconceptions held by in-serviceteachers by inviting them to participatein a teaching-learning sequence forconceptual change. Cho, Kohle andNordland (1985) defined misconceptionas conceptual and prepositionalknowledge that is inconsistent withaccepted scientific consensus. Smith,Blakeslee and Anderson (1993) describedconceptual change as a process in whichlearner realigns, reorganises andreplaces the existing misconceptions toaccommodate new concepts/ideas.Posner, Strike, Hewson and Gertzog(1982) proposed four conditions to besatisfied before a learner can replaceexisting misconception. These conditionsinclude:

1. Learner must experiencedissatisfaction with the existingconception

2. Learner should understand the newconception

3. The new conception should appearto be plausible

4. The new conception should appearto be better in explainingexperiences/ observations.

To bring in conceptual changes inthe participating in-service teachers, anopportunity was provided to the teachersto experiment and verify for themselvestheir own conceptions on the topic. Thiswas followed by discussion on possiblemisconceptions on electrochemical cellsheld by different groups as reported invarious research reports/articles. Theimplications for teaching and learning ofthe topic based on the findings of theresearch are also discussed.

Method

The study was conducted on a sampleconsisting of 22 in-service teachers whowere Trained Graduate Teachers (TGTs)working in different Jawahar NavodayaVidyalayas in the country, 90 pre-serviceteachers (undergoing secondary levelteachers’ training) and 38 pupils fromclass XII of Jawahar NavodayaVidyalaya, Munduli. The in-serviceteachers were undergoing training in acamp as a part of quality improvementprogramme. Out of 90 pre-serviceteachers, 28 were from the final year of4 year integrated B.Sc. B.Ed. Course,who have opted for applied chemistrysubject and the rest were from the finalyear of 2 year B.Ed. course, who haveopted for physical science as one of themethod subjects. Except for the pupils

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of class XII, all others in the sample viz.,in-service and pre-service teachers hadtheir schooling and college studies fromdifferent institutions of the country. Thisaspect indirectly has taken care of thepossibility of teachers’ misconceptionsaffecting the study.

What concepts are to be taught inthe area of electrochemistry at secondarylevel is decided by the chemistry syllabusframed by the Central Board ofSecondary Education (CBSE). Thefollowing topics are prescribed for studyat secondary level:

1. Sources of Electric current

(a) Voltaic cell

(b) Daniel cell

(c) Dry cell

2. Electric current - charges in motion

3. Chemical Effect of Electric current

(a) Conductivity of solutions

(b) Electrolysis

(c) Electroplating

4. Faraday’s laws of Electrolysis

The test items were developed largelybased on the syllabus related toelectrochemical cells and the principlesinvestigated by the test are generally of

basic/fundamental in nature. Each ofthe nineteen items constituting the testwas either multiple-choice or true - falsetype and investigated teachers’/pupils’understanding of electrochemical cells.For a clear reflection on the under-standing of chemical processes atmolecular level, some of the multiple-choice type items included visualconceptual questions (especially onelectrode reactions).

Results and Discussion

As it is not practically possible to discussin detail the results of the analysis of allthe test items item-wise, only significantfindings are described along withcomments on the overall performance ofin-service teachers, pre-service teachersand pupils.

The Mean scores and standarddeviation for each of the groups thatparticipated in the study is presented inTable 1.

There was no significant differencebetween the Mean score of in-serviceteachers and that of pre-service teachersand pupils. The research studies of Buttsand Smith (1987), Finley, Stewart andYarroch (1982) suggest that the studentsfind the topic on operation of cells

Table 1: Group Means and Standard Deviation for all items in the Questionnaire

Group N Mean SD t-values

1 and 2 1 and 3

In-service Teachers (1) 22 8.81 2.57 0.55 0.97

Pre-service Teachers (2) 90 8.43 2.97

Pupils (3) 38 9.47 2.36


difficult. The inability of students tomaster certain basic concepts in thetopic, perhaps, handicaps them evenafter taking up teaching assignments atsecondary level. Another interestingfinding of the study is that among thepre-service teachers, the four-yearintegrated B.Sc.B.Ed. students appearedto possess a better understandingof the basic principles of electrochemicalcells. This is evident from Table 2 inwhich the Mean score of Four yearintegrated B.Sc.B.Ed. students issignificantly different from that oftwo-year B.Ed. students. The pupils’Mean score did not differ significantlyfrom the Mean score of pre-serviceteachers undergoing B.Sc.B.Ed. course.However, the pupils’ Mean score differedsignificantly from that of pre-serviceteachers undergoing two-year B.Ed.programme.

The reasons for this significantdifference could be many. One of thepossible reasons could be that the four-year integrated students join the courseafter +2 and study the content integratedwith methodology all through the fouryears where as two-year B.Ed. students

join the course after graduation/post-graduation and concentrate more onpedagogical aspects and less on contentcompetencies.

The pre-test was administered to in-service teachers, who were undergoingtraining in a camp. According toChampagne, Gunstone and Klopfer(1985), Roth, Anderson and Smith (1987)and Smith, Blakeslee and Anderson(1993) any conceptual changeinstructions involve discussions onpossible students’ misconceptions. As afollow-up, the participants were exposedto experiments on electrochemical cellsand it was followed by a thoroughdiscussion on the generalmisconceptions of pupils in the area asreported by Sanger and Greenbowe(1999) and (2000), Garnett and Treagust(1992). This session enabled theteachers to come across a variety ofpupils’ misconceptions in the area andcompare their own understandings withthose of pupils. This exercise brought ina visible conceptual change in theparticipating teachers and this wasevident from the post-test scores assummarised in Table 3.

Table 2: Comparison of Mean Scores of Pre-service Teacher Groups and Pupils

Group N Mean SD t-values

1–2 1–3 2–3

4 - yr B.Sc.B.Ed (1) 28 9.82 2.90 3.08* 0.52 3.19*

2 - yr B.Ed (2) 62 7.8 2.81

Pupils (3) 38 9.47 2.36

* Significant at 0.01 level

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Since chemical processes takingplace on molecular level can’t bepractically seen during experimentation,one of the effective ways to understandsuch processes is through eithercomputer animation or static visuals. Inthe absence of animations, the authorsused static visual conceptual questions

to investigate into the in-serviceteachers’, pre-service teachers’ andpupils’ understanding of reactionstaking place at the electrodes in simplevoltaic and Daniel cells. Some of thequestions, which led to the identificationof misconceptions in teachers, are asfollows:

Table 3: Comparison of Pre-test and Post-test Scores of In-service Teachers

Group N Before activity After activity t-value

Mean SD Mean SD

In-service Teachers 22 8.81 2.57 11.86 3.34 3.37*

* significant at 0.01 level

On simple Voltaic Cell (a diagrammatic representation given)

Q. 1. Which of the following describes best the reaction-taking place in solution atthe zinc electrode?

Q.2. Which of the following best describes the reaction-taking place in solution atthe copper electrode?


True or False Type Questions True False I don’tKnow

Q.3. Electrons flow through the wire towards zinc electrode ( ) ( ) ( )

Q.4. The electrode sign convention in electrochemical cells ( ) ( ) ( )and Electrolytic cell is same

Q.5. Graphite can be used instead of copper electrode ( ) ( ) ( )

On Daniel Cell (a diagrammatic representation given)

Q.6. Which of the following best describes the reaction-taking place in solution atthe copper electrode?

Q.7. Which of the following best describes the reaction-taking place in solution atthe zinc electrode?

True or False Type Questions True False I don’tKnow

Q.8. The electrons flow from copper electrode to zinc ( ) ( ) ( )electrode in the external circuit.

Q.9. The function of salt bridge is to allow the migration ( ) ( ) ( )of electrons from one solution to another.

Q.10. If zinc (s) and zinc sulphate (aq) are replaced with ( ) ( ) ( )silver (s) and silver nitrate (aq), copper is oxidized.

The results of the analysis of responses to the above static visual conceptualquestions and True or False type questions are summarised in Table 4.

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Table 4. Spread of views on Electrochemical Cells held by In-service andPre-service Teachers and Pupils

Question No. Group Response (%)

Visual Questions (i) (ii) (iii) (iv)

1. In-service 4.5 4.5 36 40.5Pre-service 18.8 12.2 46.6 14.4Pupils 29 29 31.5 10.5

2. In-service 31.5 54 —- 9Pre-service 22.2 32.2 20 6.6Pupils 34 26 23.6 15.8

6. In-service 27 36 4.5 22.5Pre-service 25.5 25.5 8.8 28.8Pupils 21 36.8 29 13.2

7. In-service 10 4.5 36 18Pre-service 15.5 26.6 24.4 18.8Pupils 26.3 31.5 15.8 26.3

Question No. Group Response (%)True False I don’t Know

True/False Type Questions

3. In-service 41 50 9Pre-service 43 55 2Pupils 40 60 —

4. In-service 23 41 38Pre-service 45 42 13Pupils 21 74 5


8. In-service 45 36 19Pre-service 60 36 4Pupils 53 47 —-

9. In-service 72 5 23Pre-service 49 40 11Pupils 68 32 —-



Visual Conceptual Questions

Q.1. About 40% of in-service teachersand 18% of the total sample believed thathydrogen ions in solution acceptelectrons at zinc electrode in voltaic cell.On further probing, different reasonswere cited for this view and they aresummarised below:

(a) Hydrogen gas is liberated at zincelectrode because we see gasbubbles surrounding this electrode

(b) Hydrogen ions in solution acceptelectrons at zinc electrodeliberating hydrogen gas

(c) Electrons are available around zincelectrode in solution

(d) Zinc reacts with acid giving zincions. The electrons lost from zinc areavailable at the zinc electrode forhydrogen ions.

Q.2. About 54% of in-service teachersand 40% of total population believed thatcopper ions are produced from copperelectrode in the voltaic cell. On furtherprobing, the following reasons were citedfor the option:

(a) Copper is cathode and so electronslost by copper move to anode in thewire

(b) Electrons lost by copper move tozinc electrode through solution andthen to copper through wire

(c) Electrons are available in solutionaround copper electrode.

Q.6. On Daniel cell, about 25% of thesample opted for (i) whereas 22% optedfor (iv). The reasons quoted for the choiceinclude:

(a) Copper ions are formed from copperat this electrode

(b) The electrons lost by copper movethrough wire to zinc electrode —leading to flow of current. Currentflow detected by deflection inammeter

(c) Copper ions are formed by the lossof electrons and these electronsmove into solution.

Q.7. About 36% of in-service teachersand 25% of total population believed thatthe electrons lost from zinc would moveinto solution.

True or False Type Questions

Q.3. About 42% of the populationbelieved that the electrons flow throughthe wire towards zinc electrode in voltaiccell.

The reasons cited for the responseinclude the following:

(a) Zinc is anode (+) as it loses electronsand Copper is cathode ( - ) as it gains

electrons. Electrons flow fromcathode to anode

(b) Zinc loses electrons and theseelectrons reach the copper electrodethrough solution and then passfrom copper to zinc through the wire

Q.4. About 30% of the sample believedthat the electrode sign convention inelectrolytic cells and electrochemicalcells is same. The reason quoted for thebelief was —

● Anode is always positive andcathode is always negative.

Q.5. A majority of the sample – 63% ofpupils and 58% of pre-service teachers

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believed that graphite couldn’t be usedinstead of copper electrode for thereasons:

(a) Graphite may not work, as it is aninert electrode

(b) Graphite being non-metal, it will notconduct electricity.

Q8. About 60% of pre-service teachers53% of total sample believed that inDaniel cell, electrons flow from copperelectrode to zinc electrode in the externalwire. The reasons for holding this viewinclude:

(a) Zinc loses electrons. These movetowards copper in solution and thenflow from copper to zinc through wire

(b) Copper is cathode here. That’s whyelectrons flow from copper to zinc.

Q.9. A major group corresponding to 72%of in-service teachers, 68% of pupils and49% of pre-service teachers were of theopinion that salt bridge allows migrationof electrons from one solution to another.The explanations given for holding theview include

(a) Without salt bridge how electronsmove to complete the circuit?

(b) There will be flow of current only ifelectrons could flow through saltbridge

(c) Salt bridge establishes a connectionbetween two half cells by allowingflow of electrons.

Q.10. About 38% of pre-service teachersand 47% of pupils had a notion that inDaniel cell, when copper and silver areused as electrodes, copper is not oxidizedbecause –

(a) Among silver and copper, silver ismore reactive and so it can be easilyoxidized

(b) Copper is very less reactive thanmany metals like zinc, iron, etc.

(c) Standard oxidation potentialsdecide this. Oxidizing strength ofcopper appears to be higher.

The analysis of responses given bythe pre-service teachers and pupils andthe ensuing discussion with them led theauthors to believe that the under-standings held by pre-service teachersand pupils were more or less similar tothe understandings of in-serviceteachers.

The in-service teachers, after theadministration of Questionnaire onElectrochemical cells, were exposed toconceptual change instructions as a partof inservice training. The instructionsinclude experimentation on Voltaic andDaniel cells, representation of chemicalprocesses on molecular level throughvisual pictures and discussion onpossible misconceptions of students inelectrochemical cells. The post-test wasconducted after a gap of one week on thelast day of the training programme.Although there was a markedimprovement in the overall performance,the participants did not fare much betteras expected particularly in the visualconceptual questions category. Oninvestigation, it was found that teacherswere not comfortable in answering staticvisual questions because of unfamiliarityand confusing nature of the picturesdepicted. This could be due to the factthat the visual conceptual questions are


not generally used in textbooks andclassrooms for teaching-learningprocesses. Nurrenbern and Pickering(1987), Pickering (1990) and Sawrey(1990) have also expressed similar viewsin their research reports. Willows (1978)and Dwyer (1979) reported about thedistractive nature of static visual picturesand Dwyer concluded that such picturesneed more processing time and betterabilities to understand and work with.

Conclusions

The present study enabled theinvestigators to identify somemisconceptions that are common to thewhole sample, which consisted of in-service teachers, pre-service teachersand pupils. The most commonlyencountered misconceptions in thesample are summarised in Table 5.

The results also suggest that theconceptual change instruction strategyadopted in the study is effective inremoving misconceptions of in-serviceteachers. The implications of the presentstudy for teaching and learning ofelectrochemical cells at secondary levelare as follows:

● Electrochemistry being a difficulttopic for students to understand,simple chalk and talk method willnot facilitate learning of basicconcepts

● Experimentation on galvanic cells,explanation of various chemicalprocesses at electrodes throughstatic visual pictures and athorough discussion on possiblemisconceptions in learners wouldhelp students to learn the basicconcepts better.

Table 5: Some Misconceptions of In-service and Pre-service Teachers andPupils in Electrochemical Cells

1. Electrons flow in solution 2. Electrons flow from anode to cathode in solution 3. The flow of electrons in solution and in external circuit constitute an electric

current 4. Electrons flow through the Salt bridge 5. Salt bridge facilitates migration of electrons from one half cell to another 6. Anode is always positively charged and cathode is always negatively charged. 7. Silver is more easily oxidized than copper 8. Cathode is negatively charged and electrons move from copper (cathode) to zinc

(anode) in Daniel cell 9. Inert electrodes can’t be used as no reaction takes place at these electrodes 10.10. Anode is positively charged due to loss of electrons and cathode is negatively charged

as it gains electrons11. Hydrogen gas is liberated at zinc electrode in voltaic cell12. Copper ions are formed at copper electrode in voltaic cell.

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REFERENCES

BUTTS, B. AND SMITH, R. 1987. What do students perceive as difficult in HSCChemistry? Australian Science Teachers Journal, 32(4),45 - 51.

CHAMPAGNE, A.B. GUNSTONE, R.P. AND KLOPFER, L.E. 1985. Effecting changes incognitive structures among physics students, Cognitive structures andconceptual change, Academic Publications, Orlando.

CHO, H. KAHLE, J.B. AND NORDLAND, F.H. 1985. An investigation of high schooltextbooks as sources of misconceptions and difficulties in genetics andsome suggestions for teaching genetics, Science Education, 69, 707–719.

DRIVER, R AND EASLEY, J. 1978. Pupils and Paradigms. A review of literaturerelated to concept development in adolescent science students, Studiesin Science Education, 5, 61-84.

DRIVER, R. AND ERICKSON, G. 1983. Theories-in-action: Some theoretical andempirical issues in the study of students’ conceptual frameworks inscience, Studies in Science Education, 10, 37–60.

DWYER, F.M. 1979. The communicative potential of visual literacy:researchand implications, Educational Media International, 2, 19 - 25.

FINLEY, F.N. STEWART, J. AND YARROCH, W.L. 1982. Teachers’ perceptions ofimportant and difficult science content, Science Education, 66,531 - 538.

FINLEY, F.N. STEWART, J. AND YARROCH, W.L. 1982. Teachers’ perceptions ofimportant and difficult science content, Science Education, 66, 531 -538.

FISCHER, K.M. AND LIPSON, J.I. 1986. Twenty questions about student errors,Journal of Research in Science Teaching, 23, 783-893.

GARMETT, PAMELA J. AND TREAGUST, DAVID F. 1992. Conceptual difficultiesexperienced by senior high school students of electrochemistry: Electriccircuits and oxidation reduction equations, Journal of Research inScience Teaching, 29 (2), 121-142.

GARMETT, PAMELA J. AND TREAGUST, DAVID F. 1992. Conceptual difficultiesexperienced by senior high school students of electrochemistry:Electrochemical (Galvanic) and Electrolytic cells, Journal of Research inScience Teaching, 29 (10), 1079-1099.

GILBERT, J.K. OSBORNE, R.J. AND FENSHMAN, P.J. 1982. Children’s science and itsconsequences for teaching, Science Education, 66, 623 - 33.

GREENBOWE, T.J. 1994. An interactive multimedia software programme forexploring electrochemical cells, Journal of Chemical Education, 71 (7),555 - 557.

NURRENBERN, S.C. AND PICKERING, M. 1987. Concept learning versus Problemsolving: is there a difference? Journal of Chemical Education, 64, 508-510.


OGUDE, A.N. AND BRADLEY, J.D. 1994. Ionic conduction and electrical neutralityin operating electrochemical cells, Journal of Chemical Education, 77(1),29-34.

PFUNDT, H. AND DUIT, R. 1991. Students’ alternative framework and scienceeducation (bibliography). West Germany: Institute for Science Education,University of Kiel.

PICKERING, M. 1990. Further studies on concept learning versus problemsolving, Journal of Chemical Education, 67, 254 - 255.

POSNER, G.J. STRIKE, K.A. HEWSON, P.W. AND GERTZOG, W.A. 1982. Accommodationof a scientific conception: toward a theory of conceptual change, ScienceEducation, 66, 211 - 227.

ROTH, K. ANDERSON,C.W. AND SMITH E.L. 1987. Curriculum materials, teachertalk, and student learning: case studies on fifth-grade science teaching,Journal or Curriculum Studies, 19,527 - 548.

SANGER, M.J. AND GREENBOWE, T.J. 2000. Addressing student misconceptionsconcerning electron flow in aqueous solutions with instruction includingcomputer animations and conceptual change strategies. InternationalJournal of Science Education, 22(5), 521 - 537.

SANGER, M.J. AND GREENBOWE, T.J. 1999. An analysis of college chemistrytextbooks as sources of misconceptions and errors in electrochemistry.Journal of chemical Education, 76 (6),853 - 860.

SANGER, M.J. AND GREENBOWE, T.J. 1997. Common student misconceptions inelectrochemistry: galvanic, electrolytic and concentration cells. Journalof Research in Science Teaching, 34,377 - 398.

SAWREY, B.A. 1990. Concept learning versus problem solving - revised. Journalof Chemical Education, 67, 253 - 254.

SMITH, E.L. BLAKESLEE, T.D. AND ANDERSON, C.W. 1993. Teaching strategiesassociated with conceptual change learning in science. Journal ofResearch in Science Teaching, 30, 111 - 126.

WILLOWS, D. 1978. A picture is not always worth a thousand words: picturesas distractors in reading. Journal of Educational Psychology, 70, 255 -262.

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Teaching Aids inMathematics and Manualfor their Construction

R.P. MAURYA

Department of Education in Science andMathematics, NCERT, New Delhi 110 016

HE FASCINATING world ofmathematics provides anunlimited scope to mathe-

maticians to percive problems pertainingto three situations visualised in the formsof concrete, abstraction and intuition.However due to abstraction and intuitionsome of the mathematical conceptsbecome more complicated sometimeseven for teachers also who are activelyengaged in mathematics teaching atdifferent stages. This needs theexhaustive training in methods as wellas in contents. This also needs theclarifications of mathematical conceptsusing teaching aids, eperimentation,observation and practicals etc. inmathematics to avoid the abstraction atdifferent stages of schooling.

T

In the present paper, manuals havebeen given for some of the teaching aids,which can help in preparing theteaching aids to conduct thedemonstration and practicals inmathematics at school level. Many moreactivities may be designed by the teacherin classroom to motivate the students toprepare and conduct the same by theirown.

1. Topic – The sum of internal anglesof a triangle is 180°.

Material Required – Drawing sheet (thinply board), Tape, Knife, Blade and Scale.

Method of Construction

1. Cut drawing sheet in a triangularshape.

2. Now cut this triangular drawingsheet according to the lines DE, EFand DG.

3. Join the cutting parts by tape.

4. Fold the three angles ∠ 1 , ∠ 2, ∠ 3along the line DG, DE ad EF. We seethat ∠ 1, ∠ 2, ∠ 3 make a straightline, i.e., sum of the internal anglesof a triangle is 180°.

Fig. 1 Fig. 2 Fig. 3

73TEACHING AIDS IN MATHEMATICS ANDMANUAL FOR THEIR CONSTRUCTION

II. Topic – The total surfac area of acylinder is 2πr (r + h).

Material Required – Thick paper sheet.


1. Take a thick rectangular papersheet of length l and breadth b.Then area of this sheet will be l . b

2. Fold this sheet to make cylinder

3. Now we see that cylinder has twocircular ends. If radius of these endsare r then area of each circular end= πr2.

4. If cylinder is made by folding thickpaper sheet along length thenheight of cylinder h = l (say) andcircumference of circular end is 2πr= b (say)

5. Now curved area of cylinder will beequal to the area of rectangularpaper sheet.

Now, area of the curved part = areaof thick rectangular paper sheet

= l . b= h . 2pr= 2prh

6. Hence total surface area of cylinder

= 2 . (pr2) + 2prh = 2pr (r + h)square unit.

III. Topic – Minimum five things areessential to construct a definitequadrilateral.

Material Required – Five very thin longstrips of wood, Nails.

Method of construction

1. Take such four strips of wood andjoin them with nail end to end.

2. Now we see that we can change theshape of formed quadrilateral bychanging the direction of strips.

3. Join another strip diagonally in thequadrilateral.

4. New quadrilateral has a definiteshape and no other quadrilateralcan be formed by given fivemeasurements.

Fig. 1 Fig. 2

Fig. 1 Fig. 2

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5. Hence we can prove by this modelthat minimum five things arenecessary to construct a definitequadrilateral.

IV. Topic – To approve the identity :(a + b)2 = a2 + 2ab + b2

Material Required – Drawing sheet,Tape, Coloured paper, Knife, Blade andScale.


1. Cut a square of length a (say) ofdrawing sheet. So the area of thissquare ABCD will be a2.

2. Cut another square of length b. Soarea of this square FGHC will be b2.

4. Total area of these fourquadrilaterals

= area of squre ABCD + area ofsquare FGHC

+ area of rectangle EFCD +area of rectangle CHIB

= a2 + b2 + ab + ab = a2 + b2 +2ab

5. Now, join these four quadrilateralswith the help of tape as shown inFig. 5.

6. Now length of new big quadrilateralAIGE is (a + b) and breadth is also(a + b).

So the area of new quadrilateral =(a + b)2

Hence (a + b)2 = a2 + 2ab + b2

V. Topic – The area of a circle of radiusr is πr2.

Material Required – Paper sheet,Fevicol, Knife, Blade and Scale.


1. Make a circle (say, of radius r) withthe help of knife.

Fig. 1 Fig. 2 Fig. 3 Fig. 4

Fig. 5


2. Now we fold the circular paper sheetas shown in the Figure 2. Now wepress and open the sheet and writenumbers 1 to 16 on divisions.

Fig. 1 Fig. 2

3. We cut the 16 divisions and arrangethem as shown in the figure.

4. This is quite obvious that theultimate figure is rectangle.Therefore the area of this rectanglewill be the area of circle.

5. Now, area of rectangle = length .breadth

=12

(Circumference of circle) .

(Radius of circle)

= πr2

6. Hence the area of circle = πr2

VI. Topic – Area of a parallelogram isthe product of length of any parallelline and the distance(perpendicular) between them.

Material Required – Drawing sheet,Tape, Knife, Blade and Scale.


1. Cut drawing sheet in the shape ofparallelogram ABCD with the sidesa and b.

Fig. 1

Fig. 2

2. Draw a line DE perpendicular on ABand cut the triangle ADG. Now joinΔ ADG and quadrilateral DGBC withtape.

3. We cut another triangle CBEcongruent to Δ ADG and join it withtape as shown in the Figure 3.

Fig. 3

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Fig. 3

Fig. 4

4. Now we fold the Δ CBE in back side.Now we have to find out the area ofparallelogram ABCD.

But area of parallelogram ABCD =Area of Δ ADG + Area ofquadrilateral DGBC

= Area of Δ CBE + Area ofquadrilateral DGBC

(Q Δ ADG ≅ D CBE)

= Area of rectangle DGEC

5. Now we fold Δ ADG in back side andopen the Δ CBE

Therefore,area of parallelogram =Area of rectangle DGCE

= CD . DG= a . h

VII. Topic – Angles inscribed in thesame arc of a circle are equal.

Material Required – Plyboard, Nails,Thread, Protractor and Scale.


1. Take a plyboard of rectangularshape. Then we draw a circle withcentre O on plyboard.

2. We mark the points P, Q, R, A, B, C,D, E on the circle and fit the nailson these points.

3. Now, we choose an arc let P Q R.After this we show the angleinscribed in the arc P Q R byhanging the threads.

4. We measure the different angleinscribed in arc PQR with the helpof protractor.

5. We see that all angles have samemeasure. Hence angles inscribed inthe same arc of a circle are equal.



VIII. Topic – Angle in a semi-circle isalways right angle.




2. Now, we take a diameter PQ on thecircle and fasten the nails on P andQ points.

Fig. 1 Fig. 2

3. We fasten the nails on circle at pointA, B, C, D, E, F, . .

4. Now by hanging the thread we showthe angle subtended by the (semi-circle) diameter.

5. After this we measure the anglevalues of different angles subtendedby the diameter.

6. We find that all angles are rightangle. Hence angle in a semi circleis always right angle.

IX. Topic – Angle subtended by an arcat the centre is always double theangle it subtends at any point of theremaining part of circle.




2. Now we mark the points P, Q, R, A,B, C, D on the circle as shown inFigure 2.

Fig. 3


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3. Now we choose an arc let PQR andwe fasten the nails on P, Q, R, A, B,C, D, . . .

4. After this we get subtended angleby arc PQR at the centre andmeasure it.

5. Then we measure subtended anglesby arc PQR at any point of theremaining part of circle.

X. Topic – To prove the identity : (a –b)2 = a2 – 2ab + b2

Material Required – Drawing sheet,Tape, Coloured tape, Knife and Scale.


1. Cut a square of length suppose a ofdrawing sheet. So the area of thissquare will be a2.

6. We get that this angle is the half ofangle subtended at the centre.

7. Hence angle subtended by an arcat the centre is always double theangle it subtends at any point of theremaining part of the circle.

2. Cut a square AGEF of length bfrom square ABCD as shown in theFigure 2.

3. We cut the square ECHI andrectangle DIEF and EHBG fromremaining part.

Fig. 5


Fig. 4


4. We join all parts as to make squareABCD with the tape.

5. Now we have to find out the area ofsquare CHEI.

So, Area of square CHEI =area of square ABCD – [areaof square AGEF + area ofrectangle DIEF + area ofrectangle GBHE]

or, (a – b)2 = a2 – [b2 + (a – b) b+ (a – b) b]

= a2 – [b2 + ab – b2 + ab – b2]

= a2 – [2ab – b2]

or (a – b)2 = a2 – 2ab + b2

XI. Topic – Sum of interior angles of aquadrilateral is 360°.

Material Required – Thin plyboard,Knife, Fevicol and Scale.


1. Cut a quadrilateral ABCD with knifeand denote its angles by writing 1,2, 3 and 4.

2. Now, divide the quadrilateral ABCDinto four parts as denoted by thethin lines in the adjoining figure.

Fig. 1

3. We draw a line OX on anotherplyboard sheet.

Fig. 2

4. Now, we paste the angle 1 on thissheet such that vertex A imposedon O and one side on OX.

5. After this we paste the another threeparts such that vertex of each part(angle) imposed on O and sidestouch the sides of other angle.

Fig. 3

6. Now, we may see that Δ 1, Δ 2, Δ 3,Δ 4 makes 360°. Hence Δ 1 + Δ 2 +Δ 3 + Δ 4 = 360°.

XII. Topic – In a right angled trianglethe square of hypotenuse is the sumof square of remaining two sides ofthe triangle.

Material Required – Plyboard, LEDs,LED circuits, Wire and Battery.


1. We take a plyboard and constructthe right angled triangle ABC on it.

O X

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Fig. 1

2. Now, we construct a square onsides AB, BC and CA respectivelyas shown in the Figure 2 and putthe sticks showing the lines KB andCD respectively. After this we put astick showing the line CM which isperpendicular to AB.

Fig. 2

3. We fix the LED on A, B, C, D, E, F, H,K, L and M and make different

circuit for D ABC, D KAB, D CAD, ACHK, GCBF, ABED andrectangle ALMD.

4. Now we have to demonstrate by thisparticular aid that area ( ABED)= area ( BCGF) + area ( ACHK).

For this purpose we show by LEDcircuits that

Δ KAB ≅ Δ CAD ......(i)

and area (Δ CAD) = 12

area

( ALMD) ......(ii)

Similarly we can show that

area (D KAB) = 12

area

( ACHK) ......(iii)

But area (D KAB) = area (D CAD)

......(iv)

Thus,

area ( ALMD) = area ( ACHK) (v)

Similarly we can prove that

area ( LBEM) =area ( GCBF)(vi)

Now area ( ABED) = area ( ALMD) + area ( LBEM)

= area ( ACHK) + area( GCBF)

or AB2 = AC2 + BC2

or h2 = b2 + l2

XIII.Topic – The sum of all exteriorangles of a convex polygon is 360°.

Material Required – Thin plyboard,Knife, Scale and Blade.



1. First of all we cut the different typesof polygons on this plyboard, say,pentagon as shown in Figure 1.

Fig. 1

2. Now we take any one of polygonsand cut the angles from polygon asshown in Figure 2 on plyboard.

3. We touch the vertex of all angles.

4. We see that all angles make a circleas shown in Figure 3. Hence we cansay that sum of exterior angles of apolygon is 360°

i.e., ∠ 1 + ∠ 2 + ∠ 3 + ∠ 4 + ∠ 5 =360°

XIV. Topic – To introduce the differenttypes of quadrilaterals.

Material Required – Thin plyboard,Knife, Tape and Scale.


1. Cut three shapes of right angledtriangle on plyboard as themeasurement given in Figure 1.

Now cut two trapeziums of samemeasurement on plyboard asmeasurement given in the followingFigure.

Fig. 2

Fig. 3

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2. Join three triangles and twotrapeziums by hinges or tape in thefollowing sequence.

Fig. 4

3. If we fold ABEI part we get a squareIHGE.

If we fold Δ ABC, we get rectangleAHGC.

4. If we fold Δ HGF, we get theparallelogram ABFH.

5. If we fold IDGH we get rhombusABDI.

6. If we fold EGHI we get trapeziumABEI.

Fig. 1 Fig. 2 Fig.3

Fig. 5 Fig. 6


Also we can verify the properties ofdifferent types of quadrilaterals withthe help of above arrangements.

XV. Topic – To introduce the varioustypes of angles.

Material Required – Thin wooden stripsand Hinges.


1. Join the wooden strips by hinges sothat strips can move on each other.

2. Now as shown in Figures 1, 2, 3, and4 we can introduce the differenttypes of angles.

Fig. 7 Fig. 8 Fig.9

Fig. 1

Fig. 2

Fig. 3

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XVI. Topic – To introduce the concept ofpercentage.

Material Required – Chart paper, Scale,Pen.

1. Draw a square on a chart paper.

2. Divide the length and breadth inten equal part.

Fig. 4

3. Divide the whole area of square in 100 equal parts as shown in Fig. 3

Fig. 1 Fig. 2

Fig. 3


4. Now if we want to show 4% we colourfour boxes out of 100.

5. Again if we want to show 15% wecolour 15 boxes out of hundred andso on.

Fig. 4 Fig. 5

This is just a sample of some ofactivities/practicals which can becarried out in a classroom situation withlow cost material using waste materialfrom surroundings or enviroment. Ateacher may explore many more basedon the mathematical concepts at

different stages of schooling. Suchactivities can instantly motivate thestudents and create an environment formathematics learning. The teacher mayencourage students to perform similaractivities to make mathematics learningmore joyful.

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Scieence Student–Teacher’s Reflection UponIntelleectual andProcedural Honesty onConducted Practicals

A.C. PACHAURY

110-B, Sushmita, Sector-A, SarvdharmBhopal-462042

CIENCE for all up to secondarystage was envisaged makingfuture citizens literate and

endowed with scientific temper. Teachingof the prescribed scientific content andremembering it by the students neitherdevelops nor nurtures scientific outlookand attitude in them. Properunderstanding and appreciation ofscientific concepts can only come byengaging learners in processes andprocedures that unearth unknowncharacteristics possessed by thephysical, chemical or biological realitiesthat they can investigate at their level ofcognitive functioning.

Brown and Brown (1972) conducteda study on the American Professors ofScience regarding what constitutescientific values according to them. Onthe basis of semantic differentialtechnique of Osgood et al, theydelineated ten scientific values.Intellectual and procedural honesty wasranked III by them. Other values rankedI to X were Curiosity; Integrity; Creativity;Open-mindedness; Experimental

S

verification; Commitment andpersistence; Cause-and-effect; andSkepticism. Sampled Indian Science-teachers had marked intellectual andprocedural honesty from ranks III to VIII;(Pachaury, 1973; 2003a, b, 2004).Students develop this and other scientificvalues when they conduct, biology,chemistry and physics practicals duringtheir higher secondary; B.Sc. and M.Sc.courses. The main concern of presentstudy has been to ascertain howintellectual and procedural honesty hadbeen practised by the science student-teachers when they had engagedthemselves in performing sciencepracticals during their schooling andundergraduate/post-graduate studies.

Sample: 30 graduate and postgraduate science student-teachers whowere studying in a B.Ed. College of newBhopal township participated in thisstudy (18 men and 12 women). Theirmodal age was 22 years.

Data collection: An opinionnaireconstructed by the investigator formedthe tool for data collection. Theparticipants were requested to marktheir responses on the following five pointpercentages. A 0-10%; B 11-25%; C 26-50%; D 51-75% and E 76-100%.

When you did biology, chemistry andphysics practicals/ experiments duringhigher secondary, B.Sc. or M.Sc.courses, how often did you

(i) wrote objectives of the experiment/practical in your own language?

(ii) collected your data step-by-step?

(iii) analysed and did calculations onthe collected data?

87SCIENCE STUDENT–TEACHER’S REFLECTION UPONINTELLECTUAL AND PROCEDURAL HONESTY ...

(iv) interpreted/ reported on your owndata?

(v) took help from external sources inwriting objectives, data collection,analysis/ calculations, inter -pretation and reporting?

Results: The accompanying tableprovides how often the sampled sciencestudent teachers had responded on thefive administered queries. They are allexpressed in percentage.

Ques- A B C D Etion

I 30 33 30 03 03

II 27 17 23 20 13

III 20 17 23 40 –

IV 13 17 33 33 03

V 30 33 17 17 03

(Percentages have been rounded off)

In all 93% (A, B and C) of the sampledscience student-teachers accepted thatfor about half of all the experiments doneby them, they did not write objectives intheir own language. Similarly 67% didnot collect their data step-by-step. Thispercentage was 20 and 13 for up to761100 times, respectively. 60% of thesestudent-teachers also did not analyze,did calculations on their collected data.However, 40% did so for 50-75 times ofexperiments done by them. A little morethan 60% of them did not interpret orreport on their own collected data. Only33% and 3% did so for 76/100 times,respectively. As many as 97% of themadmitted that they resorted to the use ofexternal sources in writing objectives,

collection of data, analysis andcalculations, interpretation andreporting up to 75% of time. By anycriterion, this is very low index ofintellectual and procedural honestydisplayed by the sampled sciencestudent-teachers on the practicalsconducted by them.

Discussion: From the point of view ofdevelopment of scientific temper amongthe science student-teachers, this is notencouraging at all. It appears theverificatory character of the conductedpracticals failed to tempt their awe forknowing something new. This, therefore,dampened their enthusiasm andepistome in investigating already knownfacts. Apart from this, it was thoughtuseful to ascertain the reason thatcaused this situation. Five subjects fromeach gender category of the respondents’interview revealed interesting facts. Non-monitoring of the practicals by theconcerned staff being one of them. Theother is related with the staff biases inboth the internal and externalassessments. The respondents assertedthat this thwarted their self-esteem aswell.

Educational implications: In theopinion of the investigator, all theseobservations to a very large extent canbe easily tackled. In order to shakestudents’ monotony in engagingverificatory exercises/practicals, it issuggested to modify the nature of thepracticals. Experimental/investigatoryactivities can be conceived by theteaching staff on the basis of thescientific concepts learnt in the theoryclasses. It shall be useful only when

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some orientation of the students is firstdone with regard to

● the nature of scientific investigation

● generation of a hypothesis

● its experimental testing by isolationand control of variables

● conducting the experiment

● analysis and drawing of data basedinference and

● collection and reporting of datahonestly

Besides these, issues like what isobjectivity, how law of parsimony works,and why replicability are essentialingredients of an experiment need to be

thoroughly discussed before studentsembark on exploration of newrelationships constructed in the form ofa hypothesis. A slender percentage of thestudents in all possibility would be pronefor violating rules of doing an experimentproperly. Such incidences can bereduced by individual monitoring andthrough interactive dialogue on thereasons for resorting to dishonestpractices.

Lastly, but not the least, staffdisplaying intellectual and proceduralhonesty in their day-to-day behaviorshall provide a positive and reinforcingrole model for the development andnurture of these scientific values in theirstudents.

REFERENCES

BROWN, S.B. AND BROWN, L.B. 1972. A semantic differential approach to thedelineation of scientific values by professor of science and humanities;Journal of research in Science Teaching, 4, 345-351.

PACHAURY, A.C. 1973. Scientific values of science teachers, Indian EducationalReview, 39,6, 140-141.

PACHAURY, A.C. 2003 a. Perception of scientific values held by the elementaryteacher educators, in nurturing values through School Education; Reportof the Regional Seminar, RIE, Bhopal (February 6-8).

PACHAURY, A.C. 2003 b. Tribal school biology teachers’ perception of scientificvalues; Journal of Value Education, 3, 1, 106-109.

PACHAURY, A.C. 2004. Tribal school +2 science teachers’ perception of scientificvalues; Journal of Indian Education (accepted).

89W A T E RPOLLUTION

Water Pollution

PUSHPLATA VERMA

Lecturer in Zoology, RIE, Ajmer

OLLUTION is one of the majorenvironmental problems thesedays. The term pollution has been

defined in a variety of ways.According to E.P. Odum, pollution is

an undesirable change in the physical,chemical or biological characteristics ofour air, land and water that will harmfullyaffect the human life and the desirablespecies, or that may waste or deteriorateour raw material resources.

In Environmental (protection) Act,1986 of India “environmental pollutant”means any solid, liquid or gaseoussubstance present in suchconcentration as may be or tend to beinjurious to environment; and‘environmental pollution” means thepresence in the environment of anyenvironmental pollutant. There are twobasic types of pollutants.

Non-degradable Pollutants— Thematerials and poisonous substancessuch as aluminium cans, mercurialsalts, long chain phenolic chemical, andDDT that either do not degrade or degradeonly extremely slowly in the naturalenvironment are called non-degradablepollutants.

The non-degradable pollutants alsocombine with other compounds in theenvironment to produce additionaltoxins. The obvious and sensiblesolution, which is of course not so easy

P

to practice, is to ban the dumping ofsuch materials into the environment, orto stop production of such substancesentirely by replacing them withdegradable substances.

(b) Biodegradable Pollutants—Pollutants such as the domestic sewagecan be rapidly decomposed by thenatural processes or some artificialsystems that enhance nature’s greatcapacity to the decompose and recycleare called biodegradable pollutants.

Heat or thermal pollution can beconsidered in this category since it isdispersible by the natural means.However, serious problems arise with thedegradable type of pollutants when theirquantity into the environment exceedsthe decomposition or dispersal capacityof the environment.

Water Pollution— Water is one of themost important natural resources and aregular supply of clean water is veryessential for the survival of all livingorganisms. Any physical, biological, orchemical change in water quality thatadversely affects living organisms ormake water unsuitable for desired usescan be considered pollution. There aremany natural sources that contaminatewater such as poison springs, oil seedsand sedimentation from erosion.

Pollution control standards andregulations usually distinguish betweenpoint and non-point pollution sources.Factories, power plants, sewagetreatment plant, underground coalmines, and oil wells are classified as pointsources because they dischargepollutants from specific locations, such

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as drain pipes, ditches, sewer outfalls.These sources are discrete andidentifiable, so they are relatively easyto monitor and regulate. It is generallypossible to divert effluent from the wastestreams of these sources and treat itbefore it enters the environment.

In contrast, nonpoint sources of waterpollution are scattered or diffuse, havingno specific location where they dischargepollutants into a particular body of water.Nonpoint sources include runoff fromfarm fields and feedlots, golf courses,lawns and gardens, construction sites,logging areas, roads, streets and parkinglots. Whereas point sources may be fairlyuniform and predictable throughout theyear, nonpoint sources are often highlyepisodic.

Sources of Water Pollution

Although the types, sources and effectsof water pollutants are often interrelated,it is convenient to divide them into majorcategories. Let’s look more closely atsome of the important sources ofpollution and the effects of each type ofpollutant.

Infectious Agents

The most serous water pollutants interms of human health worldwide arepathogenic organisms. Among the mostimportant water borne diseases aretyphoid, cholera, bacterial and amoebicdysentery, enteritis, polio, hepatitis andschistosomiasis. Malaria, yellow fever,and filariasis are transmitted by insectsthat have aquatic larvae. Altogether atleast 25 million deaths each year aredirectly or indirectly due to these waterrelated diseases. Nearly two-thirds of the

mortalities of children under 5 years ageare associated with water borne diseases.

The main source of these pathogensis from untreated or improperly treatedhuman wastes. Animal wastes fromfeedlots or fields near waterways and foodprocessing factories with inadequatewaste treatment facilities also aresources of disease-causing organisms.The United Nations estimates that 90percent of the people in developedcountries have adequate sewagedisposal, and 95 per cent have cleandrinking water.

The situation is quite different inless-developed countries 2.5 billionpeople in these countries lack adequatesanitation, and that about half thesepeople also lack access to safe drinkingwater. Conditions are especially bad inremote, rural areas where sewagetreatment is usually primitive ornonexistent, and purified water is eitherunavailable or too expensive to obtain.The world Health Organisation estimatesthat 80 per cent of all sickness and diseasein less-developed countries can beattributed to waterborne infectious agentsand inadequate sanitation.

Oxygen-Demanding Wastes

The amount of oxygen dissolved in wateris a good indicator of water quality andof the kinds of life it will support.

● Water with an oxygen content above6ppm will support game fish andother desirable forms of aquatic life.

● Water with less than 2ppm oxygenwill support mainly worms,bacteria, fungi and other detritusfeeders and decomposers.


Oxygen is added to watery diffusionfrom the air, especially when turblenceand mixing rates are high, and byphotosynthesis in green plants, algae,and cyanobacteria. Oxygen is removedfrom water by respiration and chemicalprocesses that consume oxygen.

The addition of certain organicmaterials, such as sewage, paper pulp,or food-processing wastes, to waterstimulates oxygen consumption bydecomposers. The impact of thesematerials on water quality can beexpressed in term of biochemical oxygendemand (BOD): a standard test of theamount of dissolved oxygen consumed byaquatic micro organisms over a five-dayperiod. An alternative method, called thechemical oxygen demand (COD) uses astrong oxidising agent to completelybreak down all organic matter in a watersample. This method is much fasterthan BOD test, but normally gives muchhigher results because it oxidisescompounds not ordinarily metabolized bybacteria. A third method of assayingpollution levels is to measure dissolvesoxygen (DO) content directly using anoxygen electrode. The DO content ofwater depends on factors other thanpollution. But it is usually more directlyrelated to whether aquatic organismssurvive than is BOD. The effect of oxygen–demanding wastes on rivers depend toa great extent on the volume flow andtemperature of their water. In cold waterdissolved oxygen can reachconcentrations up to 10 ppm, even lesscan be held in warm water. Aerationoccurs readily in a turbulent, rapidlyflowing river, which is therefore, oftenable to recover quickly from oxygen

depleting processes. Downstream from apoint source, such as a municipal sewageplant discharge, a characteristic declineand restoration of water quality can bedetected either by measuring dissolvedoxygen content or by observing the floraand fauna that live in successivesections of the river.

Plants Nutrients and CulturalEutrophication

Rivers and lakes that have clear waterand low biological productivity are saidto be oligotrophic (oligo = little + trophic= nutrition). By contrast, eutrophic (Eu+ trophic = truly nourished) water arerich in organism and organic materials.Eutrophication is an increase innutrient levels and biologicalproductivity. The rate of eutrophicationand succession depends on waterchemistry and depth volume of inflow,mineral content of the surroundingwatershed and the biota of the lake itself.

Human activities can greatlyaccelerate eutrophication. An increasein biological productivity and ecosystemsuccession caused by human activitiesis called cultural eutrophication.Cultural eutrophication can result fromincreased nutrient flows, highertemperature, more sunlight reaching thewater surface or a number of otherchanges. Increased productivity in anaquatic system sometimes can bebeneficial. Fish and other desirablespecies may grow faster, providing awelcome food source.

Eutrophication, thus denotes theenrichment of a water body by input oforganic material or surface run-off

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containing nitrates and phosphates.Elevated phosphorus and nitrogen levelsstimulate “blooms” of algae or thickgrowths of aquatic plants, Bacterialpopulation also increase fed by largeramounts of organic matter. The waterafter these changes becomes cloudy orturbid and has unpleasant tastes andodors. In extreme cases, plants and algaedie and decomposers deplete oxygen inthe water. Collapse of the aquaticecosystem can result.

Inorganic Pollutants

Some toxic inorganic chemicals aresometimes released from weathering ofrocks and are carried by run off into lakesor rivers or percolate into ground wateraquifers. This pattern is part of naturalmineral cycles. Humans often acceleratethe transfer rates in these cyclesthousands of times above naturalbackground levels through mining;processing, using and adopting impropermethods of disposing minerals andmineral wastes.

In many areas, toxic, inorganicchemicals introduced into water as aresult of human activities have becomethe most serious form of water pollution.Among the chemicals of greatest concernare heavy metals, such as mercury, lead,tin and cadmium. Super toxic elementssuch as selenium and arsenic, also havereached hazardous levels in waters insome regions. Other elements arenormally not toxic at low concentrations.However, their higher concentration maylower water quality or adversely affectbiological communities.

Metals

Many metals such as mercury, lead,cadmium, and nickel are highly toxic.Levels in the parts per million range – solittle that you can not see or taste them– can be fatal. Because metal are highlypersistent, they accumulate in foodchains and have a cumulative effect inhumans.

Mercury Pollution

Among the naturally occurring and theindustrial pollutants, mercury is one ofthe worst offenders and a dangerouspollutants. The element is poisonous,both in the form of inorganic and organiccompounds. Methyl mercury gives offvapours. There are many records of fatalpoisoning from mercury vapours. It hasbeen found responsible for the spread offatal mercury poisoning called Minamataepidemic that caused several deaths inSweden, and Japan. The cause of deathwas due to the presence of excess ofmercury in fish (27 to 102 ppm) with anaverage of 50 ppm (on dry weight basis)that comprised a large part of thevillagers diet in these countries. The safelevel of mercury in surface water fordomestic use as prescribed by CentralPollution Control Board, New Delhi(1985) is < 0.002 ppm, the limitprescribed by the WHO (1971) is < 0.001ppm.

Mercury readily penetrates thecentral nervous system causingteratogenic effect among children bornin the Minimata area of Japan i.e. theinfants whose mothers were exposed tolarge amounts of methyl mercury were


liable to be affected with mentalretardation, cerebral palsy andconvulsions. Methyl mercury penetratesto the fetus through the placenta. Theconcentration of mercury in the bloodand the brain of the fetus was about 20%higher than in mother.

Fluoride Pollution

Sources of fluorine compounds in natureand from man’s activities, and the air-borne fluoride toxicity are one of themajor source of air pollution. Water andsoil borne problems of fluoridecompounds are also equally hazardous.Fluorine is universally present in varyingamounts in soil, water, atmosphere,vegetation and animal tissues. Becauseof its chemical reactivity, it is found innature only in combined form.

In Rajasthan, fluorosis problem hasreached threatening proportions,according to a study by the DefenseScience Laboratory in Jodhpur. Thestudy notes that fluoride haspermanently crippled over 3.5 lakhinhabitants and is likely to cripple manymore. In some cases, due to thecompression of nerves by awkwardlygrowing bones, paralysis sets in.Fluorosis is prevalent in the district ofJodhpur, Bhilwara, Jaipur, Bikaner,Udaipur, Nagaur, Barmer and Ajmer.Nagaur is among the districts where inseveral villages in fluoride pollution posesserious health hazards. Rajasthan isbelieved to have the maximum numbersof the humped back because of highfluoride concentration in water sourcesin arid and semi-arid zones. Apart fromwater, the arid and semi-arid soils are

also said to contain fluorides. Due to thisreason food grain cultivated in theseregions contains relatively higher levelof fluorides.

Lead Pollution

Lead poisoning is common in adults.Lead and processing industriesconstitute the major sources of seriouslead pollution. Though the lead paintsare greater hazards to children, who areprone to ingest and chew on paintedarticles as lead toys, painters also mayrun a risk from continual use andexposure. The lead used as stabilises insome plastic pipes is extracted by waterthereby polluting the drinking water.Lead in glazing putty may be anothersource of pollution, especially forchildren. Lead used in insecticides, foodbeverages, ointments and variousmedicinal concoctions for flavouring andsweetening is also an important sourceof lead poisoning.

Lead pollution causes liver andkidney damage, reduction in hemoglobinformation, mental retardation andabnormalities of fertility and pregnancy.The chronic lead poisoning causesGastrointestinal troubles, Neuro-muscular Effect, Central Nervous Systemeffect or CNS syndrome.

Arsenic in Drinking water

Arsenic, a natural toxin and a commoncontaminant in drinking water, may bepoisoning millions of people around theworld. Arsenic has been known since thefourth century B.C. to be a potent poison.It has been used for centuries as arodenticide, insecticide and weed killer,

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as well as a way of assassinatingenemies. Because it isn’t metabolized orexcreted from the body, arsenicaccumulates in hair and fingernails,where it can be detected long after death.The largest population to be threatenedby naturally occurring groundwatercontamination by arsenic is in WestBengal, India and adjacent areas ofBangladesh. Arsenic occurs naturally inthe sediments that make up the Gangesriver delta. Rapid population growth,industrialization, and intensification ofagricultural irrigation however have putincreasing stresses on the limitedsurface water supplies. Most surfacewater is too contaminated to drink, sogroundwater has all but replaced otherwater sources for most people in thisregion.

Non-metallic salts

Desert soils often contain highconcentrations of soluble salts,including toxic selenium and arsenic.You have probably heard of poisonsprings and seeps in the desert wherethese compounds are brought to thesurface by percolating groundwater.Irrigation and drainage of desert soilsmobilize these materials on a large scaleand can result in serious pollutionproblems. Such salts as sodium chloridethat are nontoxic at low concentrationalso can be mobilized by irrigation andconcentrated by evaporation, reachinglevels that are toxic for plants andanimals.

In many countries close to polarregions, millions of tons of sodiumchloride and calcium chloride are used

to melt ice from roads in winters. Thecorrosive damage to highways andautomobiles and the toxic effects onvegetation are enormous. Leaching ofroad salt into surface waters may havea devastating effect on the aquaticecosystems.

Sediments

A certain amount of sediment entersstreams and rivers. However, erosionfrom farmlands, deforested slopes,overgrazed lands, construction sites,mining sites, stream banks, and roadscan greatly increase the load of sedimententering water ways. Sediments (sand,silt and clay) have direct and extremephysical impacts on streams and rivers.When erosion is slight, streams andrivers of the watershed run clear andsupport algae and other aquatic plantsthat attach to rocks or take root in thebottom. These producers, alongwithmiscellaneous detritus from fallen leavesand so on, support complex food web ofbacteria, protozoa, worms, insect larvae,snails, fish, crayfish and otherorganisms which keep themselves frombeing carried downstream by attachingto rocks or seeking shelter behind orunder rocks; even fish that maintaintheir position by active swimmingoccasionally need such shelter to rest.

Sediments entering waterways inlarge amounts have an array of impacts,and, silt, clay and organic particles arequickly separated by the agitation offlowing water and are carried at differentrates. Clay and humus are carried insuspension, making the water muddyand reducing the amount of light


penetrating the water hencephotosynthesis.

Thermal pollution and Thermalshocks

Raising or lowering water temperaturesfrom normal levels can adversely affectwater quality and aquatic life. Watertemperatures are usually much morestable than air temperatures, so aquaticorganisms tent to be poorly adapted torapid temperature changes. Loweringthe temperature of tropical oceans byeven one degree can be lethal to somecorals and other reef species. Raisingwater temperatures can have similardevastating effect on sensitiveorganisms. Oxygen solubility in waterdecreases with rise in temperature. Atnormal temperature water has an oxygencontent of about 14.5 ppm, but at 80 °Cit contains only 6.5 ppm, so speciesrequiring high oxygen levels areadversely affected by warming water.

Human cause thermal pollution byaltering vegetation cover and runoffpatterns as well as by discharging heatedwater directly into rivers and lakes.

The most convenient way to removeexcess heat from an industrial facility isto draw cool water from a source like anocean, a river, a lake or an aquifer, runit through heat exchanger to extractexcess heat, and then dump the heatedwater often back into the original source.A thermal plume of heated water is oftendischarged into rivers and lakes, whererise in temperature of water can disruptmany processes in natural ecosystemsand drive out sensitive organisms. Nearlyhalf the water we draw from various

sources is used for industrial cooling.Electric power plants, metal smelters,petroleum refineries, paper mills, food-processing factories, and chemicalmanufacturing plants all use or largeamount of water for cooling and releasewater that gets heated in the process.

To minimize thermal pollution, powerplants are often required to constructartificial cooling ponds or cooling towersin which heat is released into theatmosphere and water is cooled beforebeing released into natural water bodies.

Ground Water Pollution

An exhaustive study of urban watersupply system in 75% developingcountries by Dietrich and Henderson(1963) suggested that at least 60% of thepopulation, especially in outer city areasand distant villages, is still dependenton underground sources for drinkingwater. This very important source ofwater is now threatened with pollutionfrom seepage pits, refuse dumps, septictanks, barnyard manures, transportaccidents, and with diverse agricultural,chemical or biological pollutants. Othermajor sources of groundwater pollutioninclude sewage and soluble salts. Thewidespread practice of dumping rawsewage in shallow soak pits has resultedin pollution of ground water in manycities. It attributes in the rise of cholera,hepatitis, dysentery and other waterborne diseases, especially in the regionswhere the water table is high.

Most ground water in the countrycontains trace levels of naturallyoccurring radioactive substances ortheir by-products. In addition, radioactive

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substances in ground water can resultfrom the nuclear energy programme. Atpresent there are eight functionalnuclear power stations in the countryand six more projects are in the pipeline.Operations like mining and milling ofradioactive ore, chemical reprocessingand radioactive waste disposal can alsobe source of radioactive pollution inunderground water.

Ocean Pollution

Coastal zones, especially bays, estuaries,shoals, and reefs near large cities or themouth of major rivers, often areoverwhelmed by human causedcontamination. Suffocating andsometimes poisonous blooms of algaeregularly deplete ocean water of oxygenand kill enormous numbers of fish andother marine life. High levels of toxicchemicals, heavy metals, disease-causing organisms, oil, sediment, andplastic refuse are adversely affectingsome of the most attractive andproductive ocean regions. The potentiallosses caused by this pollution amountto billion of dollars each year.

Oceanographers estimate thatbetween 3 million and 6 million metrictons of oil are discharged into the world’soceans each year from both land- andsea-based operations. About half of thisamount is due to maritime transport.Most oil spills result not fromcatastrophic, headlines accidents, butfrom routine open-sea bilge pumping andtank cleaning. These procedures areillegal but are easily carried out onceships are beyond sight of land. Much of

the rest comes from land-basedmunicipal and industrial runoff or fromatmospheric deposition of residues fromrefining and combustion of fuels.

Water Pollution Control

Appropriate land-use practices andcareful disposal of industrial, domestic,and agricultural wastes are essential forcontrol of water pollution.

(i) Source Reduction – The cheapest andmost effective way to reduce pollution isusually to avoid producing it or releasingit to the environment in the first place.Elimination of lead from gasoline hasresulted in a widespread and significantdecrease in the amount of lead in surfacewaters in the United States. Carefulhandling of oil and petroleum productscan greatly reduce the amount of waterpollution caused by these materials.Although we still have problems withpersistent chlorinated hydrocarbonsspread widely in the environment, thebanning of DDT and PCB in the 1970’shas resulted in significance reduction intheir levels in wildlife.

Modifying agricultural practices, cansubstantially reduce pollution due toexcessive use of fertilizers and pesticides.Similarly, industry can reduce pollutionby recycling or reclaiming materials thatotherwise might be discarded in thewaste stream. Both of these approachesusually have economic as well asenvironmental benefits.

It turns out that a variety of valuablemetals can be recovered from industrialwastes and reused or sold for otherpurposes.


(ii) Non-point Source and LandManagement

Among the greatest remaining challengesin water pollution control are diffuse,nonpoint pollution sources. Unlike pointsources, such as sewer outfalls orindustrial discharge pipe, whichrepresent both specific locations andrelatively continuous emission, nonpointsources have many origins andnumerous routes by which contaminantsenter ground and surface water. It isdifficult to identify let alone monitor andcontrol – all these sources and routes.Some main causes of non point pollutionare being presented here to give an idea.

The EPA estimates that 60 percentof all impaired or threatened surfacewaters are affected by sediment fromeroded fields and overgrazed pastures.Pollutants are also carried by runoff fromstreets, parking lots, and industrial sitesthat may contain salts, oil residues,pieces of rubber, metals, besides manyindustrial toxins. New buildings andland development projects such ashighway construction affect relativelysmall areas but produce vast amount ofsediment, their disposal when donecarefully, can help in reclaiming land.Generally, soil conservation methods alsohelp protect water quality. Applyingprecisely determined amounts of fertiliserand pesticides and proper irrigation notonly saves money but also reducescontaminants entering soil and watersources. The water preserving wetlandsthat act as natural processing facilitiesfor removing sediment and contaminantshelps protect surface and groundwater.In urban areas, citizens can be

encouraged to recycle waste oil and tominimize use of fertilizers and pesticides.Runoff can be diverted away from stormsand lakes. Many cities are separatingstorm sewers and municipal sewage linesto avoid flow of contaminants to watersources.

Human Waste Disposal

As we have already seen human andanimal wastes usually create the mostserious health related water pollutionproblems. More than 500 types ofdisease-causing (pathogenic) bacteria,viruses and parasites can travel fromhuman or animal excrement throughwater. The term sewage refers to thecontents of sewers carrying thewaterborne waste of a community.

The process of treatment has thefollowing advantages:

(i) The water and nutrient componentsof the sewage are recycled throughcrop irrigation or other industrialusages.

(ii) Pollution sources can be eliminated.

(iii) Pollution load can be reduced, and

(iv) Economic benefits can be achievedthrough crop yield at low cost.

Municipal Sewage Treatment

Over the past 100 years, sanitaryengineers have developed ingenious andeffective municipal wastewater treatmentsystems to protect human health,ecosystem stability and water quality.This topic is an important part ofpollution control and is a central focusof every municipal government: The

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sewage treatment includes the followingfour steps:

1. Primary Treatment– This involves theremoval of floating and suspended solids,paper, rags etc. by physical and chemicalmeans i.e. screaming, shredding,flocculating and sedimentation.Suspended matter as well as someoxygen demanding waste are removed inthe process.

Primary treatment begins as thesewage flows or pumped through thesewer pipes, bacteria initiate itsbreakdown. Partially decomposed sewageis than filtered as it enters the sewageprocessing plant. The sewage is allowedto pass through a series of coarse andfine screens to remove the large floatingobjects. The screens are usually consistsof a series of parallel bars. The waste soremoved is often passed to acomminutor/shredder where paper andrags used to shred to an acceptable size.

Though nearly 50 per cent of thematerials suspended in sewage areremoved by this treatment if water to beused for drinking purpose, it has to betreated further.

2. Secondary Treatment

This involves decomposition of theorganic material of the sewage throughmetabolic action of organismsaccelerated with abundant of oxygen. Thebreakdown is accomplished with a widevariety of organisms, including bacteria,protozoans, worms and snails. Thetechniques most commonly used are:trickling filter process and the activatedsludge process.

Trickling filters, also known asbiological filters, consist of thick bed ofgravel containing bacteria over whichthe sewage is sprinkled at a uniform rate.The filters are not less than two metresdeep and circular on rectangular in plan.When the waste water spreads over thebed, it makes contact with abundant ofoxygen. As a result, the organicmolecules in the waste get decomposed.In the activated sludge process, organicwaste and the decomposing organism aresuspended as a flocculent mass in theliquid by mechanical agitation inaeration tanks or by diffuse air. The wastecontinuously flows through the sludgetanks of about 10 feet deep, 20 feet wideand hundreds of feet long. Algae in thesludge generate oxygen to be required forthe growth and multiplication of thebacteria.

Despite the secondary treatment,some toxic chemicals, phosphatecontaining detergents and radioactivesubstances passed out unaltered. Ifsuch water is discharged, toxicsubstances may accumulate in rivers orlakes killing plants and animals.

3. Tertiary Treatment

This involves removal of some of thesuspended matter which escapes fromfinal settling tanks in the process ofsecondary treatment. Some of thetechniques which assist in their removalinclude chemical coagulation, filtration,carbon absorption and chemicaloxidation with strong oxidizing agentssuch as addition of hydrogen peroxidesand chlorine.


Fine particles are combined intoconglomerates by the process ofcoagulation the filtered out by passingthe wastewater through a bed of gravelor finally graded coal. For instancetreatment by addition of alumina-ferricfollowed by sand filtration andchlorination will yield a clear colourlesswater almost free from bacterialcontamination.

4. Sludge disposal

This involves the processing andultimate disposal of the sludge producedin sedimentation tanks. This increasesabout half of the cost of sewagetreatment. In small works, the sludge isrun on the drying beds in a thin layer of

about 150 mm deep. Their drying of thesludge takes place partly due to drainagethrough the sludge into the drains belowthe bed and partly due to evaporation bysun and wind. Within a few weeks thesludge dries. However, if the volume ofthe sludge is large, it has to be dried bymechanical means. Nowadays, mostsewage works, digest ad sludge an-aerobically to produce more stableproducts and to kill pathogenicorganisms, if present there in. Digestionmay be carried out in closed tanks.

The processed sludge is thendisposed off at some suitable sites.Disposal of sludge to farmland ispractised at many places since nutrientsare returned to the land.

REFERENCES

AGARWAL, K.C. Environmental Biology. pp. 339-376.AGARWAL, V.K. AND VERMA, P.S. Cell Biology, Genetics, Molecular Biology, Evolution

and Ecology. pp. 209-231.CUNNINGHAM, WILLIAM P., MARY ANN CUNNINGHAM AND BARBARA SAIGO. Environmental

Science, A gobal concern. pp. 387-402.RICHARD, T. WRIGHT AND BERNARD J. NEBEL. Environmental Science.

pp. 439-460.SINGH, H.R. Introduction to Animal Ecology and Environmental Biology.

pp. 275-288.

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Pluto Demoted

Pluto was stripped of its status as aplanet on 24 August 2006 whenastronomers from around the worldredefined it as a “dwarf planet”, leavingjust eight major planets in the solarsystem.

The status of Pluto as a planet cameunder a clout when in 1979 it temporarilymoved closer to the sun than Neptunein the solar system. It may be recalledthat Pluto moves in a highly ellipticalorbit around the sun. Every 248 yearsthe two planets, Neptune and Pluto, swapplaces and for about 20 years, whichimplies that Pluto becomes the eighthplanet and Neptune the ninth in termsof their distance from the sun. Thistopsy-turvy situation was rectified on11 Feb. 1999 when Pluto crossedNeptune’s orbit and became the ninthplanet once again.

But is Pluto really a planet? That’swhat astronomers have been discussingfor last decade or so when some membersof the International Astronomical Union(IAU) suggested that Pluto be given thestatus of a minor planet. Why? For onething Pluto is very small. It is 6 timessmaller than the Earth, and evensmaller than seven of the solar system’smoons (the Moon, Io, Europa, Ganymede,Callisto, Titan and Triton). Pluto’s ownmoon, Charon, is larger in proportion toits planet than any other satellite in thesolar system. Some astronomers considerthe pair to be a double planet.

Science NewsThe other reason that questioned the

status of Pluto has been its unusualelliptical orbit. It is the only planetaryorbit which crosses that of anotherplanet (Neptune), and it is tilted 17degrees with respect to the plane of thesolar system. Astronomers once thoughtthat Pluto may have been a satellite ofNeptune that was ejected to follow atilted elliptical path around the sun.However, careful simulations of the orbitsand dynamics of Pluto and Neptuneindicate that this is not likely to be so.

Pluto’s composition is unknown, butits density (about 2 g/cm3) indicates thatit is probably a mixture of rock and ice.All the other rocky planets — Mercury,Venus, Earth and Mars — are located inthe inner solar system, close to the Sun.Except for Pluto; all of the outer planets— Jupiter, Saturn, Uranus and Neptune— are gaseous giants. Once again, Plutois a misfit.

Despite its well-known peculiarities,Pluto’s official status as a planet wasnever in jeopardy until 1992 when DavidJewitt and J. Luu discovered a curiousobject called 1992 QB1. QB1 is a smallicy body, similar in size to an asteroid,orbiting 1.5 times further from the sunthan Neptune. QB1 was the first hintthat there might be more than just Plutoin the distant reaches of the solarsystem. Since then nearly 100 objectslike QB1 have been found. They arethought to be similar to Pluto incomposition and, like Pluto, many orbitthe sun in a 3:2 resonance with Neptune.This swarm of Pluto-like objects beyondNeptune is known as the Kuiper Belt,after Gerard Kuiper, who first proposed

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that such a belt existed and served as asource of short period comets.Astronomers estimate that there are atleast 35,000 Kuiper Belt objects greaterthan 100 km in diameter, which is severalhundred times the number (and mass)of similar sized objects in the mainasteroid belt.

So, is Pluto really a planet or is itmore like a dormant comet, simply thelargest known member of the KuiperBelt? That’s the question thatastronomers have recently beendebating.

Other than its relatively large size,Pluto is practically indistinguishable fromthe other Kuiper Belt Objects (KBOs) andshort period comets. The main differenceis Pluto’s reflectivity, which is muchhigher than that of known KBOs.According to Dr David Jewitt, Universityof Hawaii, USA, Pluto has a higher albedo(60%) than envisaged for the other KBOs.Albedo, it may be recalled is the fractionof sunlight that is reflected back into thespace from the surface of a planet or amoon. But this is an artifact of size -Pluto has enough mass and gravity toretain a tenuous atmosphere from whichbright surface frosts may be depositedon the surface.

In a press release dated 3 February1999 the International AstronomicalUnion stated that “No proposal to changethe status of Pluto as the ninth planetin the solar system has been made byany Division, Commission or WorkingGroup of the IAU responsible for solarsystem science. Lately, a substantialnumber of smaller objects have beendiscovered in the outer solar system,beyond Neptune, with orbits and possibly

other properties similar to those of Pluto.It has been proposed to assign Pluto anumber in a technical catalogue or listof such Trans-Neptunian Objects (TNOs)so that observations and computationsconcerning these objects can beconveniently collated. This process wasexplicitly designed to not to changePluto’s status as a planet”. However, thisview of IAU stands revised in the last weekof August 2006.

After a heated debate among 2,500scientists of the InternationalAstronomical Union (IAU) that met inPrague in August, 2006, a majority votedin favour of the proposal to demote Plutoto a dwarf planet instead of a planet. Thisfollowed the adoption of a new definitionfor a celestial body to be classified as aplanet of the solar system. According tothe new definition of planets adopted bythe IAU, a planet is an object that orbitsthe sun, forms itself into a sphere by itsown gravitational field and has enoughgravitational pull to clear its path ff spacedebris. The IAU definition also requiresthat a classical planet should be the soleoccupant of its orbit. Unlike other eightplanets of the solar system, the orbitalpath of the Pluto overlaps with otherobjects such as the planet Neptune andasteroids.

The IAU has, therefore, nowclassified Pluto as a dwarf planet andaccordingly assigned it the asteroidnumber 134340, by which it will bereferred from now onwards. With thisdecision it seems that not only the toysand models of the solar system wouldbecome instantly obsolete, but would alsocompel teachers and publishers toupdate textbooks and lessons used in

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classrooms for decades. Discovered in1930 by the American Clyde Tombaugh,the icy rock of Pluto has traditionallybeen considered the ninth planet,farthest from the sun in the solar system.

The definition of a planet, approvedafter a heated debate at the InternationalAstronomical Union (IAU) meeting inPrague, drew a clear distinction betweenPluto and the other eight planets. Theneed to define what a planet is wasdriven by technological advancesenabling astronomers to look further intospace and measure more precisely thesize of celestial bodies. According toRichard Binzel, Professor of PlanetarySciences at The Massachusetts Instituteof Technology and a member of the planetdefinition committee this is all about theadvancement of science changing ourthinking as we get more information. Thesignificance of the decision is that newdiscoveries and new science have told usthat there is something different aboutPluto from the other eight planets andas science learns more information, weget new results and new considerations.

In fact, the decades-old debate on thedefinition of a planet received impetuswhen Brown discovered UB313 in 2003.Xena, as it is nicknamed, is larger thanPluto, instantly leading to a worldwidedebate whether a new planet had beendiscovered. The scientists agreed that,to be called a planet, a celestial bodymust be in orbit around a star while notitself being a star. It must be large enoughin mass for its own gravity to pull it intoa nearly spherical shape and havecleared the neighborhood around itsorbit. Pluto was disqualified because itsoblong orbit overlaps Neptune’s. Xena

also does not make the grade of being aplanet, and will also be known as a dwarfplanet.

However, everybody does not seem toshare with the views of the IAU aboutPluto. Many members of IAU wereamazed that the agreed-upon definition,the first time the IAU has tried to definescientifically what a planet is, comes insharp contrast to the draft circulatedamongst the delegates at the GeneralAssembly. Alan Stern of the SouthwestResearch Institute in Boulder, Colorado,overseer of science investigations onNASA’s New Horizons mission to Pluto,called the reclassification rash andillogical. He is confidant that people wouldcontinue to consider Pluto a planetregardless of the decision taken at IAUmeeting. That document, which keptPluto as a planet and would have addedthree others, touched off a revolt thatgrew daily. Some delegates appeareddownright hostile to the notion. MichaelShara, Astrophysics Curator at theAmerican Museum of Natural History inNew York revealed that the Museum hadreceived enormous numbers of telephonecalls, many of which are on the vergedon hate mail from second-graders —very angry children who said, ‘what haveyou done?’ This is the cutest, mostDisney-esque of the planets. ‘How couldyou possibly demote it’?

Tombaugh’s 94-year -old widowPatricia thinks that the discoverer, likeany good scientist, would have acceptedthe demotion as inevitable. In heropinion her husband Clyde would havesaid, ‘Science is a progressive thing andif you’re going to be a scientist and putyour neck out, you’re apt to have it bitten

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upon. She added that a small amount ofher husband’s ashes were now on aspacecraft bound for Pluto.

The new definition creates a secondcategory called “dwarf planets,” as wellas a third category for all other objects,except satellites, known as small solarsystem bodies. From now on, or at leastfor the time being, traditional planets willbe restricted to eight: Mercury, Venus,Earth, Mars, Jupiter, Saturn, Uranusand Neptune. Whether Pluto remains tobe classified as a planet or a dwarf planet,the fact is that it is there deep in the solarsystem and to continue to revolve aroundthe sun in its known orbit.

(Source: NASA website)

Pluto’s Two Small Moons ChristenedNix and Hydra

What seems to be an irony of fate thaton 22 June 2006, just two months beforebeing stripped of the status of a planet,the two small satellites of Plutodiscovered in May 2005, were named Nixand Hydra by the InternationalAstronomical Union (IAU), theinternationally recognized authority forassigning designations to celestialbodies. In Greek mythology Nyx was thegoddess of darkness and the night, a veryappropriate name for a moon orbitingPluto - the god of the underworld. Toavoid confusion with the asteroid (3908)Nyx, the Egyptian spelling Nix waschosen. Hydra is the serpent with nineheads that guarded the underworld.

A team of researchers fromSouthwest Research Institute (SwRI) inBoulder, Colorado, the Johns HopkinsUniversity Applied Physics Laboratory

(APL) in Laurel, Md., the Space TelescopeScience Institute in Baltimore and LowellObservatory in Flagstaff, Ariz., usedHubble Space Telescope images to makethe discovery in support of NASA’smission to Pluto and beyond the KuiperBelt that has been named ‘New Horizons’.Alan Stern, co-leader of the discoveryteam and the New Horizons principalinvestigator from SwRI expressing hispleasure on the decision of the IAU,optimistically commented that one isgoing to be hearing a lot more about Nixand Hydra in coming years as theastronomers are already applying fortelescope time to study their orbits andphysical properties. And when NewHorizons flies by Pluto in the summer of2015, each will be mapped in detail.

(Source: NASA News on line)

TAPP-3 Synchronized with the Grid

Unit-3 of the Tarapur Atomic PowerProject (TAPP) was synchronized with thegrid on 15 June 2006. The 540 MWeUnit-3 of the Tarapur Atomic PowerProject (TAPP) attained criticality on 21May 2006 that signified the start of self-sustaining nuclear fission chain reactionin the reactor core. Designed and builtby the Nuclear Power Corporation TAPP-3 is the sixteenth nuclear power reactorin the country. With this the aggregatecapacity of NPCIL will increase to 3900MWe.

TAPP - 3 and 4 (the later hasachieved criticality on March 6, 2005)comprise two Pressurised Heavy WaterReactor (PHWR) units of 540 MWe each.PHWRs use natural uranium as fuel andheavy water both as moderator and

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coolant. The experience gained from TAPP– 3 and 4 is to be utilised for up ratingthe unit size to 700 MWe. Four such unitsof 700MWe each are proposed to be built,two units each at Rawatbhata inRajasthan and Kakrapur in Gujarat.

(Source: Nuclear India)

Optical Atomic Clock

James C. Bergquist, Physicists at theNational Institute of Standards andTechnology (NIST), Boulder, Colorado,USA has claimed that his team ofresearchers has refined an innovativeatomic clock, which would be moreprecise than the best of clocks designedduring the last 50 years. Theadvancement according to researchersmay indicate that the reign of cesiumatomic clocks is coming to an end.

To track time, a cesium clock exploitsthe absorption of microwaves by a cloudof cesium atoms. In contrast, the NISToptical clock makes use of interactionsbetween ultraviolet radiation and asingle mercury ion. Ultravioletelectromagnetic waves oscillate about100,000 times as fast as the cesium-cloud microwaves do and so provide amuch finer means to measure a second.

The NIST researchers led byBergquist having made furtherimprovements have designed a clockthat’s about 10 times as precise as theworld’s cesium standard. According toNIST figures, the cesium standard wouldbe off by no more than 1 second in 70million years of continuous operation.The NIST advance could ultimatelyimprove navigation and tele-communications systems, opines

Jean-Jacques Zondy of France’s NationalMetrology Institute in La Plaine SaintDenis. Beyond that, the achievement“raises the issue of changing thedefinition of time”, he notes.

However, a redefinition of the second,now based on a specific property ofcesium, may be decades away, accordingto Zondy. Scientists don’t yet knowwhether some other atom will provebetter than mercury in optical clocks.The record-low uncertainty of the NISTclock opens the door to ultraprecise testsof foundations of physics, includingrelativity and the steadiness of the so-called fundamental constants. Accordingto Bergquist at least one such test isalready well under way. In recent years,astrophysical data have indicated thatthe fine-structure constant called alphahas increased since the early universe.By comparing the behaviour of the newmercury clock and another NIST opticalclock based on aluminum, the NIST teamis seeking evidence that alpha may bechanging today.

(Source: Science News online)

Titan’s Lakes: Evidence of liquid onSaturn’s largest moon

New radar images indicate that Saturn’sgiant moon Titan contains lakes of liquidhydrocarbons. The finding provides thefirst compelling evidence for bodies ofliquid on the surface of any object besidesEarth, say the researchers who analysedthe images.

Located in Titan’s north polar region,the lakes range in width from just undera kilometre to 32 km and extend up to90 km. Titan’s surface, at a frigid –180°C,

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is much too cold for liquid water.According to Stephen Wall, PlanetaryScientist of NASA’s Jet PropulsionLaboratory in Pasadena, Calif, the lakesprobably consist of methane, possiblymixed with ethane. The lakes are asource of the methane gas that accountsfor 5 per cent of T itan’s smoggyatmosphere, assert Wall and hiscolleagues. Over millions of years,sunlight breaks down atmosphericmethane, and scientists have long soughta source that could replenish it. They’vesuspected that much of the moon mightbe covered with methane seas.

NASA’s Cassini spacecraft, whichbegan touring Saturn in the summer of2004, dispelled that notion. But radarimages taken by the craft on 22 July2006 show a landscape that resembleslake-strewn Minnesota. If the lakes areindeed composed of methane, thehydrocarbon would cycle between Titan’ssurface and atmosphere just as watercycles on Earth. Researchers considerthe discovery of the equivalent of ahydrological cycle on Titan quitesignificant as the finding adds yetanother reason to study the moon as itmay help scientists to unravel themystery of frozen Earth prior toappearance of life on it.

Although Titan’s hydrocarbon hazehides the moon’s surface in visible light,radar penetrates the smog. Radar-darkregions, such as the ones just found byCassini, can denote either a smooth,liquid surface or an accumulation ofpowder or sand that absorbs light.However, Wall interprets that severalsigns from Cassini paint a lakelikeportrait. Not only are the dark areas

shaped like lakes, but they also havechannels leading out of them. A smooth,dry powder or sand couldn’t sculptchannels. Furthermore, some of thelakelike areas show what appear to bemultiple shorelines, as if the body of liquidhas been receding. Millions of years ago,when methane was more plentiful, lakesmight have covered much more of themoon, suggests Jonathan Lunine of theUniversity of Arizona in Tucson, whocollaborated with Wall.

Cassini would not provide radarimages of areas near Titan’s South Poleuntil 2008. But this October, the radarsystem will look at the north polar regionof Titan from a different angle. If suchobservations over several years showchanges with season or brightnesschanges that could be caused by waves,they’ll strengthen the evidence thatliquid methane currently resides onTitan, says McEwen.


New Technique Can ManipulateLight Beams

It may be surprising to observe a laserbeam spreads when it is directed to themoon and returned by one of the mirrors,a few kilometers in diameter, left behindby the Apollo astronauts at the end oftheir trip. This spread is mostly due toatmospheric distortions, but itnonetheless poses problems to those whowish to keep laser beams from divergingor focusing to a point as light travelsthrough a medium.

Now a team of physicists,mathematicians, and electricalengineers from the California Institute

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of Technology and the University ofMassachusetts at Amherst has come outa trick to keep light pulses from divergingor focusing. Using a multi-layersandwich of glass plates alternating withair, the scientists have provided the firstexperimental demonstration of aprocedure called “nonlinearitymanagement”. This technique wouldn’tdo anything for light traveling all the wayto the moon, but could be useful infuture generations of devices involvingoptical switching and optical informationprocessing, for which precise control oflaser pulses will be advantageous.

The researchers have demonstratedthat a laser beam passing throughmultiple layers of glass and air can bemade to last much longer than if it hadpassed through only one type of medium.This procedure exploits a phenomenonknown as the “Kerr effect”, which causesthe refractive index of an individualmaterial to change if the light energy issufficiently intense. When light ispropagated only through glass, oneobtains a focused beam so intense thatit generates a plasma in the medium byionizing it. Using a multi-layer “Kerrsandwich” of light and air, however,keeps the plasma from being createdbecause the different refractive indicesof the media cause the light beam todiverge and converge several times.

However, the researchers say thatthe setup they have used is intended todemonstrate that nonlinearitymanagement can be performed, and it isnot by any means the final version of apractical apparatus.

(Source: Science Daily online)

Apple Juice BenefitsNeurotransmitter that AffectMemory

‘An apple a day keeps the doctor away’is perhaps one of the most familiarproverbs. Now a research studyconducted by scientists at University ofMassachusetts Lowell (UML)demonstrates that apple products canhelp boost brain function similar tomedication. Apples and apple juice maybe among the best foods that could beadded to our diet especially for babiesand senior citizens, according toresearchers.

Research on animals at theUniversity of Massachusetts Lowell(UML) indicates that apple juiceconsumption may actually increase theproduction in the brain of the essentialneurotransmitter acetylcholine,resulting in improved memory.Neurotransmitters such as acetylcholineare chemicals released from nerve cellsthat transmit messages to other nervecells. Such communication betweennerve cells is vital for good health, notjust in the brain, but throughout thebody.

Thomas Shea, Director, UML Centerfor Cellular Neurobiology andNeurodegeneration Research anticipatesthat the day may come when foods likeapples, apple juice and other appleproducts are recommended along withthe most popular medicines forAlzheimer’s disease. The role ofacetylcholine in the brain is not a newarea of research. Alzheimer’s medicationstudies start with the premise thatincreasing the amount of acetylcholine

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in the brain can help to slow mentaldecline in people with Alzheimer’sdisease. Testing a similar hypothesis, theUML research team found that havinganimals consume antioxidant-rich applejuice had a comparable and beneficialeffect.

In this novel animal study at UML,adult (9-12 months) and old (2-2.5 years)mice, some specially bred to developAlzheimer’s-like symptoms, were fedthree different diets (a standard diet, anutrient-deficient diet, and a nutrient-deficient diet supplemented with applecomponents (in this case, apple juiceconcentrate was added to their drinkingwater). Among those fed with the applejuice-supplemented diet, the mice showedan increased production of acetylcholinein their brains. Also, after multipleassessments of memory and learningusing traditional Y maze tests,researchers found that the mice whoconsumed the apple juice-supplementeddiets performed significantly better onthe maze tests.

The findings also suggest that theapple-supplemented diet was mosthelpful in the framework of an overallhealthy diet. Shea concludes, “Thefindings of the present study show thatconsumption of antioxidant-rich foodssuch as apples and apple juice can helpreduce problems associated with memoryloss.” According to Shea clinical studyevaluating consumption of appleproducts on humans will begin in thenear future.


Anti-obesity Vaccine Tested

In what may be the first publishedbreakthrough of its kind in the globalbattle against obesity, scientists at TheScripps Research Institute havedeveloped an anti-obesity vaccine thatsignificantly slowed weight gain andreduced body fat in animal models.

In the new study, mature male ratsimmunized with specific types of theactive vaccine ate normally yet gainedless weight and had less body fat,indicating that the vaccine directlyaffects the body’s metabolism and energyuse. This finding may be especiallyimportant to stop what is commonlyknown as “yo-yo dieting”, the cycle ofrepeated loss and regain of weightexperienced by many dieters. The newvaccine, which is directed against thehormone ghrelin (pronounced “grell-in”),a naturally occurring hormone thathelps regulate energy balance in thebody, has shown the potential, in animalmodels at least, to put an end to that riskyand often futile struggle.

Ghrelin, a gastric endocrine hormoneproduced primarily in the stomach, playsa physiological role in energyhomeostasis, although the full extent ofthat role remains unknown. It was firstidentified in 1999 as a naturally occurringligand—a molecule that binds to anotherto form a larger molecular complex—fora growth hormone secretagogue receptor.What is known is that ghrelin promotesweight gain and fat storage through itsmetabolic actions, decreasing thebreakdown of stored fat for energy as well

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as curbing energy expenditure itself.During periods of weight loss, such asdieting, the body produces high levels ofghrelin to slow down fat metabolism,encourage eating, and promote fatretention, changes which normally makeit difficult to lose weight and keep it off.There is broad speculation that ghrelinevolved as a response to the feast orfamine conditions of early humans.Those who were genetically predisposedto eat heartily and store fat efficientlyduring periods of plenty were more likelyto survive the next round of scarcity andpassed this trait onto the nextgeneration. In recent years, however,that powerful genetic legacy has come indirect conflict with the dangerousphenomenon of overeating in thedeveloped world

The findings of the researchteam may mark a turning point inthe treatment of obesity by confirmingthe effectiveness of immunopharma-cotherapy to combat this serious andgrowing global problem. Immuno-pharmacotherapy engages the immunesystem, specifically antibodies, to bindto selected targets, directing the body’sown immune response against them.This approach is being tested in anumber of other areas including drugaddiction, especially addiction to cocaineand nicotine.

According to Kim Janda, Jr.Professor of Chemistry at ScrippsResearch, the study shows that thevaccine developed by the research teamslows weight gain and decreases storedfat in rats. The research showed thateven though food intake was unchangedin all testing groups, those who were

given the most effective vaccines gainedthe least amount of weight. To have animpact on appetite and weight gain, thehormone, ghrelin, first has to move fromthe bloodstream into the brain – where,over long periods, it stimulates theretention of a level of stored energy asfat. The researchers claim that theirstudy is the first of its kind to provideevidence proving that preventing ghrelinfrom reaching the central nervoussystem can produce a desired reductionin weight gain.

However, researchers caution thattheir study does not answer all thequestions pertaining to obesity treatmentonce and for all. What the study confirmsis that this looks like a serious workablesolution to the problem. And while muchmore research is needed to understandthe full therapeutic potential ofimmunopharmacotherapy in combatingobesity, these initial results areextremely positive. Right now it appearsthat active vaccination against ghrelinis one avenue that can slow weight gainand fat build-up in the body.

A vaccine against ghrelin also isparticularly compelling in terms of thewell-documented problems of humandieting. When you diet, the bodyresponds as if it was starving andproduces ghrelin to slow down fatmetabolism and stimulate eating,changes meant to help retain and regainbody fat. As a result, many people endup regaining the weight they lost andmore once they go off their diets. Thisvaccine may have the real potential toprevent or seriously reduce yo-yo dieting;the repetitive cycle of weight loss andgain, because it interferes with ghrelin’s

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ability to promote weight gain and fataccumulation.


X-rays Reveal Archimedes’ HiddenWritings

Previously hidden writings of the ancientGreek mathematician Archimedes arebeing uncovered with powerful X-raybeams nearly 800 years after a Christianmonk scrubbed off the text and wroteover it with prayers.

Researchers at Stanford University’sLinear Accelerator Center in Menlo Parkhave been using X-rays to decipher afragile 10th century manuscript thatcontains the only copies of some ofArchimedes’ most important works. TheX-rays generated by a particleaccelerator cause tiny amounts of ironleft by the original ink to glow withoutharming the delicate goatskinparchment. According to William Noel,curator of manuscripts at Baltimore’sWalters Art Museum, the investigationis providing new insights into one of thefounding fathers of western science. It isperhaps the most difficult imagingchallenge on any medieval documentbecause the book is in such terriblecondition. It takes about 12 hours to scanone page using an X-ray beam about thesize of a human hair, and researchersexpect to decipher up to 15 pages thatresisted modern imaging techniques.After each new page is decoded, it isposted online for the public to see.

Archimedes, born in the 3rd centuryB.C., is considered as one of ancientGreece’s greatest mathematicians,perhaps best known for discovering the

principle of buoyancy while taking abath. The 174-page manuscript, knownas the Archimedes Palimpsest, containsthe only copies of treatises on flotation,gravity and mathematics. Scholarsbelieve a scribe copied them onto thegoatskin parchment from the originalGreek scrolls. Three centuries later, amonk scrubbed off the Archimedes textand used the parchment to write prayersat a time when the Greek mathe-matician’s work was less appreciated. Inthe early 20th century, forgers tried toboost the manuscript’s value by paintingreligious imagery on some of the pages.

Over the past eight years, resear-chers have used ultraviolet and infraredfilters, as well as digital cameras andprocessing techniques, to reveal most ofthe buried text, but some pages were stillunreadable. However, scientists are notoptimistic to never recover all of it.

(Source: SciCentral)

Hydrogen Power System Unveiled

A system that produces hydrogen energyto provide backup lighting and warmthhas been demonstrated at the ChewonkiFoundation’s environmental educationcenter. The nonprofit foundation teamedup with the Portland-based HydrogenEnergy Center to develop the system thatwas touted as an example of the kind ofcutting-edge technology that can reducedependence on fossil fuels and help easeglobal warming.

It is well known that hydrogenrepresents a huge growth industry, andthe researchers around the world aretrying to develop reliable hydrogen basedenergy systems. The system unveiled at

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Chewonki uses renewable power — fromsolar panels atop the center andpurchases of “green” electricity — toproduce hydrogen from water through aprocess known as electrolysis. Newtechnology that produces the gas at highpressure eliminates the need for a costlycompressor. Developers of the systemclaim that it is the first publiclyaccessible direct high-pressurehydrogen energy system as well as thefirst complete hydrogen energy system.

Because hydrogen is flammable, theelectrolyzer and eight cylinders of the gasare stored in a wood and concrete shed.The gas is then taken by a pipe, wherethree fuel cells convert it into onekilowatt of electricity. That power will beavailable in the event of an outage tosupply four days’ worth of lighting,operation of the building’s water pumpand warmth for animals that include aturtle, an iguana and an alligator.

The project, which took more thantwo years to complete, was designed todemonstrate how hydrogen can begenerated, stored and used to provideenergy. While the hydrogen generator iseducational in nature, researchers areconfident that commercial applicationsfor the technology are beginning toemerge.

(Source: Sciencenews online)

Dark Matter Spotted After CosmicCrash

An intergalactic collision is providingastronomers with a giant payoff: the firstdirect evidence of the invisible materialthat theorists say holds galaxies togetherand accounts for most of the universe’s

mass. For nearly 70 years, cosmologistshave agreed that theories of gravityaccount for observations in Earth’s solarsystem but fail on a larger scale. Forexample, if those theories heldthroughout the universe, objects on theoutskirts of the Milky Way would rotatemore slowly than those toward thecentre. But observations have revealedthat it is not so.

Scientists have offered twocompeting explanations of thisdiscrepancy. The first is that an invisiblesubstance called dark matter accountsfor 90 percent of the universe’s mass andgravity. Although scientists don’t knowwhat dark matter consists of, theypropose that it keeps each galaxy intact.However, there is another view thatdoesn’t accept existence of dark matterand that traditional models of gravitysimply need modification.

To search for dark matter, DouglasClowe of the University of Arizona inTucson and his colleagues used severaltelescopes and observatories to image anunusually energetic collision betweentwo galaxies that occurred 100 millionyears ago. Normally, as galaxies travelthrough the universe, gravity keeps darkand ordinary matter close together, so theinvisible substance can’t bedistinguished. During a galactic merger,however, hot gases from one galaxy bumpinto hot gases in the other and bothgalaxies are slowed by a force similar towind resistance. But dark matter fromone galaxy, in theory, passes rightthrough another galaxy’s dark matter.According to Clowe dark matter particlesdon’t experience the same type of dragthat slows down gas clouds. His team

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used a technique called gravitationallensing to locate the main mass in theaftermath of the collision. If dark matterdidn’t exist, all the mass would havebeen lumped together with the gases.Instead, the researchers found most ofthe mass in clumps that appeared to havewhizzed past the hot gases.

The method called gravitationallensing essentially involves observationand measurement of change in directionof light as it passes close to a massiveobjects in space. The gravity of a massiveobject, whether visible or invisible,changes the direction in which lighttravels. By observing and measuring thislight, researchers can figure out thelocation and even size of the object,whether a star, galaxy, or cloud of gas,responsible for the bending. Theresearchers focused on a galaxy clustercalled 1E0657-56 found that the gravityof something invisible and extremelymassive had bent light coming frommore-distant galaxies visible in thebackground. In fact, they detected twolarge, separate clumps. One of theclumps, the researchers say, is made ofordinary matter, consisting of hot gases.The other clump is made of dark matter.Normally, ordinary and dark matterwould be together in the same clump.

But why would dark matter separatefrom ordinary matter? During the impact,the hot gases of one galactic clusterslowed down the hot gases of the other.In contrast, because dark matter fromone galaxy passes right through anothergalaxy’s dark matter, the dark matterwasn’t slowed by the impact. So, theycould detect the two types of matter asseparate clouds.

Clowe’s team argues that only atheory of gravity that includes darkmatter can explain the separation.According to Maxim Markevitch of theHarvard-Smithsonian Center forAstrophysics in Cambridge, and amember of the research team theirfinding proves in a simple and direct waythat dark matter exists. It puts to restthe remaining doubt that cosmologistshave had until now. The matterseparation caused by the collision is“mind-boggling,” says cosmologistMichael Turner of the University ofChicago. However, he adds that theresearchers can’t rule out alternativetheories, in part because the modelsfrom them are so inconsistent.


Extending Life of Lithium Batteries

Modern rechargeable batteries forelectronic gadgets generally use lithiumcompounds as the positive electrode andhave revolutionised the electronicsindustry. They can be made very compactbut can still deliver the required voltageto run everything from cell phones todigital cameras and notebook computers.And, not forgetting those ubiquitous MP3players. However, everyone using alaptop, digital camera or a MP3 playerexperiences the frustration due tobattery discharge every now and then.As gadgetry becomes sophisticated soconsumer demands on battery life haverisen. Moreover, more powerful lithiumbatteries are beginning to be used inpower tools and may soon be seen inelectric vehicles, applications that aremuch more draining than those for whichconventional lithium batteries are used.

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A solid solution to the problem couldcome from chemists in the UK. They havedevised a new and efficient way toimprove battery power as well as makethat precious charge last longer.According to Kuthanapillil Shaju andPeter Bruce of the University, StAndrews, Scotland, lithium batteries useso-called intercalation materials as theiranode. These materials are composed ofa solid network of lithium atoms togetherwith other metals, such as cobalt, nickel,or manganese, meshed together withoxygen atoms. When one charges alithium battery, the charging currentpulls the positive lithium ions out of thisnetwork. When this battery is used, itdischarges as these lithium ions migrateback into the electrode, pulling electronsas they go, and so generating a current.

The challenge is to make newelectrode materials that deliver highpower (fast discharge) and high energystorage. Shaju and Bruce hope that theycould solve these problems by developinga new way of synthesizing a particularlithium intercalation compound (Li(Co1/

3 Ni1/3 Mn1/3)O2). As a bonus, they hopeto be able to simplify the complicatedmanufacturing process.

The St Andrews team has devised anew synthetic approach to the compoundthat involves simply mixing thenecessary precursor compounds -organic salts of the individual metals -with a solvent in a single step. This is insharp contrast to the conventional multi-step process used for making thecompound. Using this technique, theyhave been able to make highly uniformlithium oxide intercalation materials inwhich nickel, cobalt, and manganese

ions are embedded at regular intervalsin the solid, which also contains poresfor the electrolyte. The highly porousnature of the new material is crucial toits electrical properties. The pores allowthe electrolyte to make intimate contactwith the electrode surface resulting inhigh rates of discharge and high energystorage. The St Andrews team has testedtheir new lithium electrode material byincorporating it into a prototype batteryand found that it gives the battery farsuperior power and charge retention.Increasing the rate by 1000%, so thatthe battery can be discharged in just sixminutes, reduces the discharge capacityby only 12%. The test results suggestthat this approach to rechargeablebatteries could be used to make evenhigher power batteries for vehicles andpower tools. There is an added bonus inthat replacing a proportion of the cobaltused in the traditional lithium-cobalt-oxide electrodes with manganeseimproves safety by reducing the risk ofoverheating.

Flying on Hydrogen

Georgia Institute of Technologyresearchers have conducted successfultest flights of a hydrogen-poweredunmanned aircraft believed to be thelargest to fly on a proton exchangemembrane (PEM) fuel cell usingcompressed hydrogen. The fuel-cellsystem that powered the 22-foot (6.6metre) wingspan aircraft generates only500 watts. According to Adam Broughton,a research engineer who is working onthe project in Georgia Tech’s AerospaceSystems Design Laboratory (ASDL) five

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hundred watts is sufficient to light abulb, but not for the propulsion systemof an aircraft this size. In fact, 500 wattsrepresents about 1/100th the powerrequired by a hybrid car. The projectjointly undertaken by ASDL and theGeorgia Tech Research Institute (GTRI)has been led by David Parekh, DeputyDirector, GTRI and the founder of GeorgiaTech’s Center for Innovative Fuel Cell andBattery Technologies.

Parekh wanted to develop a vehiclethat would both advance fuel celltechnology and galvanise industryinterest. While the automotive industryhas made strides with fuel cells, apartfrom spacecraft, little has been done toleverage fuel cell technology for aerospaceapplications. According to him a fuel cellaircraft is more compelling than just alab demonstration or even a fuel cellsystem powering a house. It is also moredemanding. With an airplane, you reallypush the limits for durability, robustness,power density and efficiency.

Fuel cells, which create an electricalcurrent when they convert hydrogen andoxygen into water, are attractive asenergy sources because of their highenergy density. Higher energy densitytranslates into longer endurance.Though fuel cells don’t produce enough

power for the propulsion systems ofcommercial passenger aircraft, theycould power smaller, slower vehicles likeunmanned aerial vehicles (UAVs) andprovide a low cost alternative to satellites.Such UAVs could also track hurricanes,patrol borders and conduct generalreconnaissance. Fuel cell powered UAVswould have several advantages overconventional UAVs, according toresearchers. To begin with, fuel cells emitno pollution and unlike conventionalUAVs, don’t require separate generatorsto produce electricity for operatingelectronic components. Another plus,because fuel cells operate at nearambient temperatures, UAVs emit less ofa heat signature and would be stealthierthan conventionally powered UAVs.

Comet Swan

There’s a new comet in the night sky,Comet Swan. It’s a trifle too dim fornaked-eye viewing, but it is an easytarget for binoculars and smalltelescopes. Observers report a“spectacular” emerald-colored headand a long sinuous tail. All thoseinterested in tracking the comet mayvisit http://spaceweather.com for skymaps and more information.

(Compiled and edited by R. Joshi)

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Book Review

Learning Science (Parts 1 to 4)By Indumati Rao and C.N.R. RaoPublished by Jawaharlal Nehru Centre forAdvance Scientific Research, Jakkur P.O.,Bangalore 560 064. Pp.84, 148, 167, 119.

CIENCE HAS become an integral partof our lives. Applications ofscience have provided us many

benefits and ensured a better quality oflife. The world today uses a languagewhich has a lot of science in it. Evenunknowingly we use many words andphrases derived from science. It is,therefore, important to learn thelanguage of science. Not only children butalso adults have to know the rudimentsof science so that they may be able toapply the lessons learnt from science indaily life. The book under review hasbeen written keeping this very objectivein mind.

The book is in four parts. Eachpart has a different title and anindependent cover. Part 1 entitled‘Universe, Solar system, Earth’ exploresour universe, the solar system and earth.Various aspects have been covered andconcepts introduced in a simple andinterest-arousing manner. However, onpage 55, about gravitational force, theauthors write: “The strength of theforce depends upon the weight of theobject – the heavier the object, thestronger is the force.” There is a clear-cut lacunae in this statement whichshould be taken care of in the futureedition.

Part 2 is entitled ‘The world of physicsand energy: Learning physicalprinciples’. Indeed, physics has a veryimportant role to play in our daily lives.Our day begins with physics. We useheat, hear sounds and use energy. Weswitch on the fan, see TV and preservefood in a fridge, use a computer or travelto work. Our day ends with physics whenwe turn off the TV, shut down thecomputer, switch off the light and go tobed. This part includes various aspects,from levers to solar and fuel cells. Eveninformation about pacemaker andelectrocardiograph has been included.However, in the chapter on light, someelementary information about lasersshould have been included.

Part 3 is entitled ‘The world ofchemistry: of molecules and materials,Air around us, All about water.’ This partcomprises thirteen chapters in all. Thetitles of some of the chapters are ‘Whychemistry?’; ‘Water: the cradle of life onearth’; ‘Carbon: the black rock thatburns’; ‘Man and metals’; ‘Man-madematerials’; ‘Air around us’; and ‘All aboutwater’. In the chapter on Air, one alsofinds information about weather andweather forecasting. One only wonderswhether the two chapters on Water couldhave been combined into a single one.

Part 4 is entitled ‘Biology and Life’and comprises eight chapters in all. Thechapters are entitled ‘What is Biology?’,‘Evolution of life on earth’, ‘The amazingplant kingdom’, ‘Origin of the animalkingdom’, ‘Biology and life processes’,‘Same life processes but differentmethods’, ‘Energy sensors’, and ‘Theinvisible world of microbes’.

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All the four parts of the book havebeen nicely produced on glossy paperwith lots of coloured, interesting and eye-catching plates and illustrations.Certainly, the book will be useful toschool children as supplementaryreading material. It will also be useful toadults who want to learn science and

partake in the excitement of thisexperience.

P.K. MUKHERJEE

43, Deshbandhu Society15, PatparganjDelhi 110 092

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