PHYSICS and CHEMISTRY ESO 2

Antonio Ruiz Hernández

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PHYSICS and CHEMISTRY

ESO 2Antonio Ruiz Hernández

Primera edición, 2018

Autor: Antonio Ruiz Hernández

Maquetación: Ángela Fernández

Edita: Educàlia Editorial

Imprime: Grupo Digital 82, S.L.

ISBN: 978-84-948374-6-3

Depósito legal: V-2387-2018

Printed in Spain/Impreso en España.

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Student’s Book

Antonio Ruiz Hernández

PHYSICS and CHEMISTRYESO 2

UNIT 1 SCIENTIFIC ACTIVITY1. WHAT IS SCIENCE? ........................................................................................................................ 8

2. THE SCIENTIFIC METHOD .............................................................................................................. 9

3. QUANTITIES AND UNITS. SI UNITS. ............................................................................................. 11

3.1. Conversion of units. ..............................................................................................................................13

4. SCIENTIFIC NOTATION. ................................................................................................................ 14

5. THE LANGUAGE OF SCIENCE....................................................................................................... 16

5.1 Physic equations ....................................................................................................................................16

5.2. Tables and graphs. ...............................................................................................................................17

UNIT 2 MATTER PART I

1. MATTER. PROPERTIES OF MATTER ................................................................................................ 24

1.1. General properties of matter: mass & volume. ...................................................................................24

1.2. Characteristic properties: density. .......................................................................................................25

2. STATES OF MATTER ........................................................................................................................ 26

2.1. Changes in the state of matter..............................................................................................................27

2.2. Change-of-state temperature: a characteristic property. ..................................................................29

3. BEHAVIOUR OF GASES. ............................................................................................................... 30

3.1. Laws of the ideal gases. .......................................................................................................................30

UNIT 2 MATTER PART II

1. PURE SUBSTANCES AND MIXTURES. ............................................................................................ 34

1.1. Suspensions & Colloids. .......................................................................................................................36

2. DALTON’S THEORY: THE ATOM. ................................................................................................... 37

2.1. Atoms and Molecules. ..........................................................................................................................38

3. NOTATION OF ATOMS .................................................................................................................. 40

4. THE PERIODIC TABLE ...................................................................................................................... 40

UNIT 3 THE CHANGES1. INTRODUCTION ............................................................................................................................. 46

2. CHANGES IN MATTER ................................................................................................................... 46

3. HOW TO KNOW A CHEMICAL CHANGE HAS HAPPENED? ....................................................... 47

4. CHEMICAL REACTIONS. ................................................................................................................ 47

5. ANTOINE LAVOISIER: LAW OF CONSERVATION OF MASS. ...................................................... 48

5.1. Balancing chemical equations. ............................................................................................................49

6. CHEMICAL INDUSTRY. ................................................................................................................... 50

6.1. Chemistry and standard-of-life. ...........................................................................................................506.2. Sustainable Development – Sustainable Chemistry. .........................................................................51

UNIT 4 MOTION FORCES1. INTRODUCTION ............................................................................................................................. 56

2. FORCES ........................................................................................................................................... 56

2.1. What is force? .......................................................................................................................................56

2.2. Types of forces ......................................................................................................................................57

2.3. Everyday forces ....................................................................................................................................58

3. ELASTIC DEFORMATIONS ............................................................................................................. 60

4. SIMPLE MACHINES ........................................................................................................................ 61

4.1. Levers .....................................................................................................................................................61

4.2. Inclined plane .......................................................................................................................................63

4.3. Pulleys ....................................................................................................................................................63

5. LAW OF UNIVERSAL GRAVITATION. ............................................................................................ 64

5.1. Gravitation in the Universe ...................................................................................................................66

UNIT 5 ENERGY1. INTRODUCTION ............................................................................................................................. 72

2. ELECTRIC CHARGE ......................................................................................................................... 72

2.1. Static electricity .....................................................................................................................................73

2.2. Electric force. Coulomb’s law. ............................................................................................................74

3. ELECTRIC CURRENT ........................................................................................................................ 76

3.1. Electric conductors and insulators .......................................................................................................76

4. ELECTRIC CIRCUITS ........................................................................................................................ 76

4.1. Elements of an electric circuit. ..............................................................................................................77

5. ELECTRICAL QUANTITIES .............................................................................................................. 81

5.1. Voltage or electric potential difference (tension). ..............................................................................81

5.2. Electric Resistance. ................................................................................................................................82

5.3. Intensity of current. ................................................................................................................................82

5.4. Ohm’s law. ...........................................................................................................................................82

6. CONVERTING ELECTRICITY: ELECTRIC MACHINES ..................................................................... 84

unit 1SCIENTIFIC ACTIVITY

1. WHAT IS SCIENCE?

2. THE SCIENTIFIC METHOD

3. QUANTITIES AND UNITS. SI UNITS.

3.1. Conversion of units.

4. SCIENTIFIC NOTATION.

5. THE LANGUAGE OF SCIENCE

5.1 Physic equations

5.2. Tables and graphs.

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1. WHAT IS SCIENCE?

Science is a kind of organized and testable knowledge, which let scientists give a reliable prediction about a subject.Generally speaking, there are three types of Science: Experimental, Social and Formal.

• Experimental sciences are focused on the study of the Universe. Its name comes from the fact that predictions are usually tested by means of experiments carried out in laboratories. Some examples of experimental sciences are Physics, Chemistry or Bio-logy.

Physics and Chemistry study phenomena, i.e. natural facts, facts which occur in the real world.

- Physics studies the processes in which there is not a change in composition (in a physical change we have the same substances after it).

- Chemistry studies the processes in which there is a change in composition.

• Social sciences study different phenomena related to the Humanity, such as Geogra-phy, History or Psychology. Their predictions are also tested in different ways because socials scientists cannot perform experiments as experimental scientists do.

• Formal science is knowledge about abstract or non-real objects, such as numbers. Mathematics, Logic or Computer sciences are examples of Formal sciences.

EXERCISES

1. Classify the following sciences in accordance with the above explained classification: Mathematics, Geology, Psychology, Biology, Computer Science, History, Chemis-try, Physics, Sociology, Logic, Astronomy, Geography

EXPERIMENTAL SCIENCES SOCIAL SCIENCES FORMAL SCIENCES

2. Classify the following phenomena in physical or chemical:a) The falling of an apple.b) The echo.c) Evaporating water.

d) Oxidation of a nail.e) Mixing bleach and ammonia.f) Mixing salt and water

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2. THE SCIENTIFIC METHOD

The scientific method is a procedure used by all the scientists since Galileo Galilei develo-ped it in the 17th Century for the first time. These are the steps of this method:

A) Observation and asking a question The main purpose of scientific observation is raising a ques-tion related to Nature. As a matter of fact, every scientific research is an attempt to give an answer to a certain ques-tion. Example ( 1UB video): Why is that plant growing faster?

B) Formulation of a hypothesis A hypothesis is a conjecture, a statement or an explanation based on our previous knowledge of the Universe, which can explain some phenomena and be tested empirically. Example (UB video):

• Hypothesis 1. The books are making the plant grow faster.

• Hypothesis 2. The music is making the plant grow faster.

• Hypothesis 3. The sunlight is making the plant grow faster.

C) ExperimentationA scientific hypothesis must be stated in terms of measurable quantities to let us check whe-ther it is true or false. In other words, a hypothesis must give us a testable prediction so that we can know whether it is right or false after collecting the results of an experiment (or experiments).Example (UB video):

• Experiment 1. We put one plant (control) without books near to it, and another plant (the variable) near to a pile of books.

• Experiment 2. We put one plant (control) in a silent place, and another plant (varia-ble) near to music playing.

• Experiment 3. We put one plant in a dark place and the other one under a window where the sunlight can light it up.

D) AnalysisIn this stage the scientist must check what is happening with the experimentation, analysing the results (tables, graphs…).Example (UB video):

• Experiment 1. There is no significant difference between the two plants (control and variable).

• Experiment 2. There is no significant difference between the two plants (control and variable).

• Experiment 3. The plant under the sunlight grows significantly faster.

1 You can watch this video at http://physchem.tecnoruiz.es

Figure 1. Animated Science. Universitat de Barcelona

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E) Conclusion: Statement of laws and theoriesAfter analysing the results of the experiments we may be able to draw a conclusion. Example (UB video):

• Sunlight makes plants grow faster.

A scientific law is a statement which is verified empirically and has a universal applicability. Before you can say you discovered a scientific law many experiments must demonstrate it is right.

F) DisseminationThis is an important stage in modern Science. Scien-tists disseminate the results of their investigations publi-shing it in magazines, on the Internet… They can also read a lot of information about other scientists’ works and that helps them to orient their research.

EXERCISES

3. Do you think that the conclusion of the example (“Sunlight makes plants grow faster”) can be considered as a scientific law according to the method followed in the video?

4. According to the following observation, write down the rest of the steps of the Scien-tific Method you would follow.

Observation: “There’s nothing on my smartphone screen”.

Question:

Hypothesis:

o H2:

o H3:

o H4:

Experiment:

o E1:

o E2:

o E3:

o E4:

Results/Analysis:

o R/A1:

o R/A2:

o R/A3:

o R/A4

ConclusionDissemination:

Figure 2. Scientific Method Poster (www.teachers-tools.com)

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3. QUANTITIES AND UNITS. SI UNITS.

A physical quantity –or physical magnitude- is a physical property of a body or pheno-menon, which can be measured quantitatively. The height of people can be known perfect-ly, so it is a physical quantity. On the other hand, beauty cannot be measured so easily, so it is not a physical quantity.A unit is a value of a certain physical quantity, which is chosen by convention and used to fix the value of different quantities of the same kind. Measuring a physical quantity is comparing its value with the proper value of the unit. For instance, you can use the length of your hand to measure another length. In this case your unit is your own hand and the value of the length is the number of times you have to place your hand from one point of a body to the opposite one.It is very important to share the same units all over the world, so that people can trade, sell and buy products fairly. In the 19th century the General Conference on Weights and Mea-sures established the Metric System, based on 3 units (metres, kilograms and seconds). The International System of units (SI) was created in 1960 and is used by almost all countries.There are two different kinds of physical quantities: base and derived. On the one hand, a base quantity is easy to be measured and its unit can be defined uni-versally in terms of a physical constant.There are seven base quantities:

• Length is a quantity that measures the dis-tance between two points. In SI its unit is the metre.

• Mass is related to the amount of matter of a system or body. In SI it is measured in kilo-grams.

• Time measures the duration between two events. In Si it is measured in seconds.

• Temperature quantifies how cold or hot a body is. In SI it is measured in Kelvin (K).

• The amount of substance measures the number of particles (atoms or molecules) of a body. It is measured in moles, in SI.

• Electric current measures the flow of electric charges through a conductor and its unit is ca-lled Ampere.

• Finally, the luminous intensity measures in-tensity of light in candelas.

Physical quantity measured Base unit SI abbrevation

mole mol

meter m

kilogram kg

second s

Kelvin k

ampere A

candela cd

Figure 3. Seven SI basic units of measurement

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On the other hand, derived quantities can be set in terms of the fundamental ones, so we don’t need to define a specific unit for them. For instance, length is a fundamental quantity, which can be measured very easily, but area is a derived quantity because we can find its value with a formula. You can see some examples:

Derived Quantity Name Symbolarea square meter m2

volume cubic meter m3

speed, velocity meter per second m/s

acceleration meter per second squared m/s2

mass density kilogram per cubic meter kg/m3

Some units may not be adequate to measure great or little quantities. Example: to measure the mass of a pencil the kilogram is not used. In those cases, these prefixes can be used (multiples and submultiples):

Multiplier Exponent form Prefix SI Symbol1 000 000 000 000 1012 tera T

1 000 000 000 109 giga G

1 000 000 106 mega M

1 000 103 kilo k

100 102 hecto h

10 101 deca da

0.1 10-1 deci d

0.01 10-2 centi c

0.001 10-3 mili m

0.000 001 10-6 micro µ

0.000 000 001 10-9 nano n

0.000 000 000 001 10-12 pico p

EXERCISES

5. Complete the following table, indicating the type of quantity and the SI units used to measure each one

QUANTITY TYPE SI UnitsDensity Derived kg/m3

Volume

Length

Force

Mass

Time

Speed

REMEMBERA physical quantity

must include:NUMBER + UNIT

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3.1. CONVERSION OF UNITS.

Sometimes we get a physical quantity with a certain unit and we need to change it to an International System (SI) unit.For Base Quantities (revision):

A. Linear quantities (e.g. metres): To go up move the decimal point one position to

the left (or add a zero on the left). Ex: 100 m = 10 dam = 1 hm

• To go down move the decimal point one position to the right (or add a zero on the right).

Ex: 1 m = 10 dm = 100 cm

B. Quadratic quantities (e.g. m2):• To go up a step move the decimal point two posi-

tions to the left (or add zeros on the left).

Ex: 100 m2 = 1 dam2 = 0.01 hm2

• To go down a step move the decimal point two posi-tions to the right (or add zeros on the right).

Ex: 1 m2 = 100 dm2 = 10000 cm2

C. Cubic quantities (e.g. m3):• To go up a step move the decimal point three positions to the left (or add zeros on

the left).

Ex: 1000 m3 = 1 dam3 = 0.001 hm3

• To go down a step move the decimal point three positions to the right (or add zeros on the right).

Ex: 1 m3 = 1000 dm3 = 1000000 cm3

EXERCISE

6. Change these units to the different ones in brackets, using conversion factors.

a. 2.5 km (cm) e. 3 µm (mm)

b. 3 ml (l) f. 15 m2 (cm2)

c. 55 cm3 (m3) g. 15 h (s)

d. 1 m3 (dm3)

Figure 5. Magnetic Metric Staircase (www.educationalinsights.com)

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For Derived Quantities:A conversion factor is a fraction which has the same amount at its numerator and denomi-nator, but measured in different units. Conversion factors let us change a physical quantity to a different unit without changing its amount. They can be used also to convert Base Quan-tities, but it is easier using the “ladder method” explained above.

Examples:

20 m/s ---- How to convert to km/h?

300 mg/dm3 ---- How to convert to g/cm3?

300mg

dm3 =300mg

dm3 ·1 g

1000 mg=0.3

g

dm3 ·1 dm3

1000 cm3 = 0.0003g

cm3

EXERCISE

7. Change these units to the different ones in brackets, using conversion factors.

A. 55 cm3 (m3) B. 120 m2 (cm2)

C. 15 m/s (km/h) D. 3.6 g/cm3 (kg/m3)

E. 300 m3/h (dm3/s) F. 700 t/h (kg/s)

G. 70 km/h (m/s) H. 12 t/m3 (kg/cm3)

4. SCIENTIFIC NOTATION.

In science, we deal with some very LARGE numbers:1 mole = 602000000000000000000000 atoms (or molecules)In science, we also deal with some very small numbers:Mass of an electron = 0.000000000000000000000000000000091 kgImagine the difficulty of calculating the mass of 1 mole of electrons!

0.000000000000000000000000000000091 x 602000000000000000000000 ??????????????????????????????????????????????

Note:1 t = 1000 kg

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Working with such numbers is much easier using scientific notation. Scientific notation is a method of representing very large or very small numbers in the form

M x 10n

M is a number between 1 and 10 (1≤M<10)

n is an integer

Example: 2 500 000 000 would be 2.5 ·109

Example: 63.4 · 10-9 is not well written in scientific notation. Example: 6.34 · 10-8 is well written in scientific notation. Example: 0.634 · 10-7 is not well written in scientific notation.But, how do we convert a standard number to scientific notation? To convert a number to scientific notation, we count the number of places the comma is moved to have an adequate value for M (between 1 and 10). X is the number of places.a) If you moved to the left, X must be added (+) to the exponent.b) If you moved to the right, X must be taken away (-) to the exponent. Examples: 4530000 = 4.53 · 106

0.0007281 = 7.281 · 10-4

EXERCISE

8. Calculate the corresponding values in scientific notation

STANDARD NOTATION SCIENTIFIC NOTATION39500

0.073

12

43000000

7

1000000000000

0.00002413

104

0.0007 · 108

36.21 · 105

9. Calculate the corresponding values in standard notation.

STANDARD NOTATION SCIENTIFIC NOTATION3.6 · 105

1.8 · 10-3

8.48 · 109

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5. THE LANGUAGE OF SCIENCE.

To communicate the results of any scientific research scientists use a very accurate langua-ge, including physic equations, data tables and graphs.

5.1 PHYSIC EQUATIONS

A physic equation is a mathematical expression that relates physical quantities. For exam-ple, velocity is defined as the space travelled by an object in a certain period of time:

𝐯𝐯𝐯𝐯 =𝐬𝐬𝐬𝐬𝐭𝐭𝐭𝐭

Equations help us calculate quantities as the velocity of an object, but they are also useful to find out the relation between two quantities. Two of the most common relations between quantities are direct proportionality and inverse proportionality.Two quantities are directly proportional when multiplying one by one number the other goes multiplied by the same number.Two quantities are inversely proportional when multiplying one of the quantities by one number the other is divided by that number. According to that definitions, velocity (v) is directly proportional to space(s), whereas is inversely proportional to time (t).

EXERCISE10. According to the following equation:

P =FS

a) What is the relation between P and S?

b) What is the relation between P and F?

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5.2. TABLES AND GRAPHS.

Graphic representation is another way of analysing numerical data. Graphs enable us stud-ying the cause and effect relationship between two quantities. Graphs help to measure the extent of change in one variable when another variable changes by a certain amount.To draw a graph we need a set of data. In science it is common to gather the results of an experiment in data tables like this one:

STUDY OF THE ELONGATION OF A SPRING

m (kg) Δl (cm)

0 0

1 3

2 6

3 9

4 12

5 15

We are going to use that data table, which comes from the experimental study of the elon-gation of a spring with different weights, to illustrate the process of creating a graph.To start drawing a graph you need to count on graph paper (squared). Then you have to follow these steps: Step 1: Draw two perpendicular axes. The horizontal axis (X) will be used for the inde-pendent variable (the one we control and change in an experiment). The vertical axis will be for the dependent variable. You write down the name and unit of each variable beside each axis.

Figure 6. Elongation of a spring (Svjo - Wikipedia)

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Step 2: Find the range in values. There are two sets of values. What units are used? What are the greatest value and the least value for the first set? What are the greatest value and the least value for the second set? In our examples the quantities are mass and elongation. The mass ranges from 0 to 5 and the elongation ranges from 0 to 15. Step 3: Determine a Scale and draw the units on both axis. Start with the horizontal scale. In our example we have 30 squares available in the horizontal axis, and the mass starts with 0 and gets to 5 kg, so we could make 6 squares equal 1 kg, to maximise the use of the graph paper. The vertical scale must always start at 0 (this is very important, and your teacher will let you know why). Consequently, in our example graph the vertical scale will range from 0 to 15. In the vertical axis we have 30 squares and the highest value is 15 cm, so we could make each two square equal 1cm.Important: Each axis can have its own divisions, but once you have decided how many squares equal a certain value, it has to be the same for the rest of the values for that axis

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Step 4: Plot the points and connect them. Plot a point for each pair of values. Which item of a pair is indicated by the horizontal scale? And by the vertical scale? How many points will you plot? Connect the points with straight lines from left to right.

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Step 5: Give the graph a title. What is your graph about?

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Elongation of a spring with different weights

When two variables are directly proportional, we get a graphic like this one. When the in-dependent variable (mass) increases the dependent variable (elongation) increases by the same rate. If we represented in-versely proportional quantities, the graph would be like the one in figure 7.:To sum up, the procedure for constructing a line graph follows these steps:

• Step 1: Draw two perpendicular axes.

• Step 2: Find the range in values.

• Step 3: Determine a Scale and draw the units on both axis.

• Step 4: Plot the points and connect them.

• Step 5: Give the graph a title

0,00

0,50

1,00

1,50

2,00

2,50

3,00

0 10 20 30 40 50 60

P (atm)

Figure 7. Pressure vs Volume

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EXERCISE

11. In 2000, a law was passed against the use of cell phones while driving in Anytown, N.Y. The number of people who use cell phones while driving in Anytown has chan-ged each year since then as shown in the table below. Construct a line graph to visually display this data.

Cell Phone Use While Driving in Anytown, NYYear Number of People

2000 309

2001 274

2002 256

2003 238

2004 197

2005 203

2006 195

2007 192

12. Measuring the volume occupied by a fragment of a mineral according to its mass we get this set of values

m(g) 10 20 30 40 50

V(mL) 4 8 12 16 20

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REVISION EXERCISES

1. Change these units to the different ones in brackets, using conversion factors when necessary

28kg (g) 1850.2cm2 (m2)

3cg (hg) 0.35km2 (dam2)

324500mg (kg) 65g (µg)0.65 dag (mg) 65dm3 (L)

320 cm (m) 50m3 (dm3)

755 m (hm) 0.3dm3 (mL)

2.5 dam (cm) 30ºC (K)

150 mL (hL) 143K (ªC)

33 cL (mL) -45ºC (K)

750 dL (cL) 90m/S (km/h)

150 min (s) 540km/h (m/s)

10800 s (h) 4.2km/min (m/h)

20.25m2 (dm2) 200cm/s (m/min)

136.g/cm3 (kg/dm3)

2. Change these units to SI units, using conversion factors when necessary.

a. 300000 km/s b. 75 g/cm3

c. 108000 km/h d. 6.2 µg

e. 6.2 mm/min f. 6700 mg/cm

g. 1.6 g/cm3 h. 120 cm/min

i. 4285 mm/h j. 450 mg/mm2

k. 1.2 hg/dm3 l. 1224 km/h

m. 6 mg/dm2 n. 485 dag/L

o. 540 m/h

3. Convert these values to scientific notation.

a. 1001 b. 0.13592

c. 53 d. 0.0038

e. 6926300000 f. 0.00000013

g. 3920000 h. 0.567

i. 0.00361

4. Convert these values to standard notation

a. 1.92 · 103 b. 1.03 · 10-2

c. 3.051 · 101 d. 8.862 · 10-1

e. 4.29 · 102 f. 9.512 · 10-8

g. 6.251 · 109 h. 6.5 · 10-3

i. 8.317 · 106

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5. In the following table you have the data of the solubility of Oxygen (O2) in water at different temperatures.

a. Draw the graph corresponding to these data (in your notebook, use a whole page in vertical orientation).

b. How does the solubility of O2 in water vary with temperature? What is the relation between these two magnitudes?

c. How could affect the action of the sunlight in the summer to the aquatic life in a pond?

Temperature (ºC) Solubility (µg/100g)0 1420

5 1230

10 1090

15 980

20 880

25 810

30 750

35 700

6. Studying the motion of an object the following data are obtained

Position (cm) 4 16.5 24 29 54

Time (s) 0 5 8 10 20

a) Represent the graph of Position vs. Time.

b) Point out, in the graph, the Time that corresponds to the Position 40 cm.

c) Find out, extrapolating, the position that would correspond to the Time 22s

7. We hang different weights from a spring, getting different elongations according to this graph:

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5 10 15 20 25 30 35 40 45 50

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5

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mass (kg)

a. What is the relation between mass and elongation?

b. What would be the elongation for 20 kg?

c. What weight do we need to get an elongation of 60 cm?

unit 5ENERGY

1. INTRODUCTION2. ELECTRIC CHARGE

2.1. Static electricity2.2. Electric force. Coulomb’s law.

3. ELECTRIC CURRENT3.1. Electric conductors and insulators

4. ELECTRIC CIRCUITS4.1. Elements of an electric circuit

5. ELECTRICAL QUANTITIES5.1. Voltage or electric potential difference (tension).5.2. Electric Resistance.5.3. ntensity of current.5.4. Ohm’s law.

6. CONVERTING ELECTRICITY: ELECTRIC MACHINES

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1. INTRODUCTION

Electricity is all around us powering technology like our smartphones, computers, lights, air conditioners... It’s tough to escape it in our modern world. Even when you try to escape electricity, it’s still at work throughout nature, from the lightning in a thunderstorm to the sy-napses inside our body. But what exactly is electricity? Electricity is briefly defined as the flow of electric charge, but there’s so much behind that simple statement. Where do the charges come from? How do we move them? Where do they move to? How does an electric charge cause mechanical motion or make things light up? So many questions! You are going to find the answer to all the questions throughout the following sections of this unit :

Video ( What is electricity?)

2. ELECTRIC CHARGE

As we studied in Unit 2, matter is made up of tiny fundamental particles called atoms. Insi-de each atom it is possible to differentiate two zones: nucleus (protons and neutrons) and orbitals (electrons). In these orbitals electrons are continuously moving, rotating around the nucleus. With respect to the electric charge of each one of the three basic subatomic particles, re-member:

Figure 1. Lightning in a thunderstorm

Figure 2. What is electricity? – Origin Energy YouTube Channel

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• Protons: They are positively charged (+).

• Neutrons: They have no charge.

• Electrons: They are negatively charged (-).

The particles responsible for all electric phenomena are the electrons, because they can escape the orbit of the atom.In general, materials are neutral, i.e., they contain the same number of negative charges (electrons) and positive charges (protons). However, under certain circumstances electrons can move from one material to another creating positively charged bodies (with less electrons than protons) and negatively charged bodies (with more electrons than pro-tons). This way neutral bodies become electrically charged, by losing

or gaining electrons. One property of electric charges is that those of the same sign repel one another whereas tho-se of opposite sign attract each other. This effect is due to the presence of an Electromagnetic Field (EMF), which can be defined as a physical field of forces produced by electrically charged particles

Exercise

58. Give three examples of artificial use of electricity and another three examples of the presence of electricity in natural processes.

59. Find out the sign of the charge of the following ions (electrically charged atoms):

a) Fluorine atom with 10 electrons.

b) Lithium atom with 2 electrons.

c) Carbon atom with 7 electrons.

d) Calcium atom with 18 electrons.

Now say what would happen if the ion a) and the ion c) met each other.

2.1. STATIC ELECTRICITY

Static electricity exists when there is a build-up of opposite charges on objects separated by an insulator. Static (as in “at rest”) electricity exists until the two groups of opposite charges can find a path between each other to balance the system out.To acquire electric charge bodies need to gain or lose electrons. Many bodies get charged when we rub them. If we rub a pen with a wool sweater or a piece of cloth we see that it can attract small pieces of pa-per. We say that the pen is now electrically charged. This phenomenon happens because some electrons passed from the wool to the pen, and it got negatively charged

Figure 3. Atom of Carbon

Figure 4. Repulsion/Attraction of Charges

Figure 5. Electric slide – Ken Bosma on flickr.com

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Video (The science of static electricity):

Exercises

60. Inflate a rubber balloon. Rub it over a wool sweater for about 30 seconds. Then place it near your hair. What happens? Can you explain this phenomenon?

2.2. ELECTRIC FORCE. COULOMB’S LAW.

In 1785, Charles Augustin de Coulomb (1736-1806), French physicist and engineer pre-sented in the Academy of Sciences in Paris a report with the results of his experiments with charged bodies, and his conclusions could be summarised in the following points:

• Charged bodies experience an attraction/repulsion force when they the get close one another.

• The value of this force is directly proportional to the product of the value of their char-ges.

• The value of this force is inversely proportional to the square of the distance separa-ting these charges.

• If the charges are the same sign the forces are repulsion forces, and it they are oppo-site sign they are attraction forces.

These conclusions make up what we know nowadays as the Coulomb’s Law: “The elec-trostatic force with which two charges attract or repel each other is directly proportional to their product and inversely proportional to the distance between them”. This force acts in the direction of the straight line defined by the position of both charges. Mathematically:

𝑭𝑭𝑭𝑭 = 𝒌𝒌𝒌𝒌 ·

𝒒𝒒𝒒𝒒𝟏𝟏𝟏𝟏 · 𝒒𝒒𝒒𝒒𝟐𝟐𝟐𝟐𝒓𝒓𝒓𝒓𝟐𝟐𝟐𝟐

Where:F is the electrostatic force of attraction/repulsion in Newton (N). q1 and q2 are the values of the charges in Coulombs (C).r is the distance separating the centre of both bodies in metres (m). k is the electrostatic constant depending on the medium where the charges are (in vacuum, its value is 9·109 N·m2/C2).

Figure 6. The science of static electricity – TED-Ed YouTube

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If F is an attraction force, its value is negative, because charges are opposite sign (-·+ =- and +·- =- ). On the contrary, if F is a repulsion force it is a positive value, because charges are the same sign (+·+ =+ and -·- =+).

Exercise

61. Go back to Unit 4, and look for the Newton’s Law of Universal Gravitation. Compa-re it with Coulomb’s Law. What do they have in common? What is different between them?

62. Calculate the force between charges of 5.0·10-8 C and 1.0·10-7 C if they are 5.0 cm apart.

63. What is the magnitude of the force a 1.5·10-6 C positive charge exerts on a 3.2·10-4 C negative charge located 1.5 m away?

64. Two equal charges of magnitude 1.1·10-7 C experience an electrostatic force of 4.2·10-4 N. How far apart are the centres of the two charges?

65. Two charged spheres 10 cm apart attract each other with a force of 3.0·10-6 N. What force results from each of the following changes, considered separately?

a) Both charges are doubled and the distance remains the same.

b) Same charges but separation increased to 20 cm.

Figure 7. Interactive Coulomb’s Law – physicsclassroom.com

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3. ELECTRIC CURRENT

As opposed to static electricity where charges gather and remain at rest, we talk about electric current when charges can constantly flow. Thus, we can define an electric current as a flow of electric charge. Current electricity is dynamic, charges are always on the move.

3.1. ELECTRIC CONDUCTORS AND INSULATORSNot all materials allow the flow of electric charge. Some materials don’t permit the electrons to circulate whereas some other let the electrons flow easily.Electric conductors are materials that have electrons that can move freely. When connected to a source of electric current, conductors allow the flow of elec-trons through them. Metals are good electric conductors.Electric insulators are materials whose electrons cannot circulate freely, such as ceramics, glass, plastics, paper,… These materials do not conduct the electric current.

Exercises

66. Indicate which ones of the following materials are conductors and which ones insu-lators:

a) A spoon (steel) e) A piece of paper

b) A wooden fork f) A copper wire

c) A plastic container g) Rubber gloves

d) Aluminium foil

4. ELECTRIC CIRCUITS

When a body is negatively charged and another body is positively charged, we say there is a certain electric potential difference between them. When we connect two points with different electric potential using a conductor element, electrons will flow through it from the element with excess of electrons to the one with lack of them, creating an electric current. This current will continue until both points reach the same electric charge (electric balance). To understand this process, we can use the hydraulic analogy.

- Video (What is electricity?)

Figure 8. Examples of electric conductors and insulators

Figure 9. What is electricity? – Curiosity Machine YouTube Channel

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An electric circuit is a set of connected components through which an electric current circulates. The practical application of electric circuits is to bring electricity from the generating elements (like batteries) to the receiving elements (like light bulbs or motors) that convert the electricity in other forms of energy like heat, light or motion.We can find this electric potential difference in a battery, which has two zones with different charges (positive pole and nega-tive pole). If we connect both poles with an electric conductor (cable), electric current will appear. The greater the difference in electric potential, the stronger will the electrons flow through the conductor.

4.1. ELEMENTS OF AN ELECTRIC CIRCUIT.

An electric circuit can count on five types of fundamental elements: generators, conductors, receptors, control elements and protection elements. For a circuit to work the three first elements of this list are absolutely necessary.

• Generators are the elements that supply circuits with the electric energy. They pro-voke the electric potential difference. Batteries, power supplies, dynamos and al-ternators are examples of generators. Generators produce electric energy from a different source of energy, like motion or a chemical reaction. Batteries have two poles, one positive (cathode) and one negative (anode). By convention, the electric current is considered to flow from the positive pole to the negative pole of a battery

Electric Symbol Pictures

• Conductors allow the electric current to flow through a circuit, from the generators to the receptors. Conductors are formed by a material with a good electric conductivity (low electric resistance). Cables, protoboards and printed circuit boards are exam-ples of conductors. Cables are normally composed of a set of copper wires (conduc-tor) covered by a plastic jacket (insulator).

Figure 10. Example of basic electric circuit

Figure 12. Electric Cable by Petar Milošević on Wikipedia

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• Receptors are those elements capable of using the flow of electric current to produce an effect. They transform the electric energy into another type of useful energy: mo-tion (motors), heat (resistors), light (LEDs, light bulbs), sound (bells or buzzers)

Electric Symbol Picture Name

Motor

Light bulb

Resistor

Light Emitting Diode (LED)

Bell

Buzzer

• Control elements are devices that allow us to open (disconnect) or close (connect) a circuit when we need it. Some examples of control elements are:

� A switch (simple), allows us to open or close a circuit staying in the same position until we act on it again.

� A push button allows us to open or close a circuit only while we are acting on it. When we stop pushing the button it goes back to its original position. We can dis-tinguish between a normally closed push button (NC) and a normally open push button (NO).

� A 3-way switch is an element that establishes an association between one input and two possible outputs. This association is permanent while the 3-way switch is not actioned again. One application of the 3-way switch is to be able to turn on or off a circuit from two different remote locations, as some lights at home

Electric simbol Picture Name

Switch

Push button

3 way Switch

Figure 13. Symbols/Pictures of Receptors

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• Protection elements protect the circuit from voltage overloads and the people from possible accidents.

� Fuses are formed by a metal thread that melts when there is an overload, opening the circuit. It prevents delicate components from burning.

� Residual-Current Device (RCD) is a typical element in home electric circuits, and it protects the users from a malfunction of the system

Electric simbol Picture Name

Fuses

RCD

Figure 15. Symbols/Pictures of

Exercises

67. A very simple example of circuit is the one that makes a car horn sound. Indicate the type of element of every part of this circuit:

The button we push to make the horn sound is a:• Receptor

• Generator

• Control element

The battery of the car is a:• Generator

• Control Element

• Receptor

The horn is a:• Generator

• Control Element

• Receptor

68. Draw the diagram of a circuit with a battery, a NO push button and a light bulb, and explain its operation.

69. Draw the symbol of the following elements and identify the type of element they are.

Picture Symbol Type of element

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Picture Symbol Type of element

70. Copy these diagrams in your notebook and identify the elements of the following circuits. Then explain their operation.

F.E.

D.C.

B.A.

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5. ELECTRICAL QUANTITIES

To understand the operation of electric circuits we need to know the electrical quantities that characterise them. The ones we are going to study this year are: voltage, resistance and intensity. Remember that a physical quantity is a property that can be measured.

5.1. VOLTAGE OR ELECTRIC POTENTIAL DIFFE-RENCE (TENSION).

A battery supplies a circuit with the necessary energy for the electric charges to circulate. All batteries indicate in their characteristics the value of the given voltage. Tension or voltage (V) is the energy by charge unit supplied by a battery or power supply. Voltage is mea-sured in Volts (V). When we talk about potential difference we refer to the different energy by charge unit in two different points of a circuit. Using the analogy with a water circuit, a battery acts like a pump, giving pressure to the water. The higher the power of the pump, the stronger will the water flow. The higher the voltage of the battery, the higher the energy of the flowing electric charges.

If several batteries are connected in series, their electric potential difference (voltage) ag-gregate (for example, 6 batteries of 1,5 V give a total voltage of 9 V)

Video (Voltage):

Figure 16. Six 1,5V batteries in series

Figure 17. Voltage - SeeBox YouTube

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5.2. ELECTRIC RESISTANCE.

Electric Resistance (R) is a measurement of the opposition of a material to the flow of elec-tric current. It is measured in Ohms (Ω). Electric conductors have a low resistance, allowing the current to easily flow through them. Electric insulators have a very high resistance, prac-tically not allowing the electrons to pass through them.All the receptors in an electric circuit (light bulbs, motors,…) have a certain resistance. Con-sequently the flow of electric current gets more difficult as we add more receptors to a circuit.

Exercise

71. If we need a copper wire with a high electric resistance, which one of the following options is the best one:

a) A long thick wire

b) A short thick wire

c) A long thin wire

d) A short thin wire.

5.3. INTENSITY OF CURRENT.

Intensity of current (I) is the amount of electric charge that passes through the section of a conductor in a second. It is measured in Amperes (A).

5.4. OHM’S LAW.

Georg Simon Ohm (1789-1854) was a German physicist and mathematician known prin-cipally for his research on electric current.Ohm’s law relates Voltage, Resistance and Intensity of current. It states that the intensity of current circulating in a circuit is directly proportional to voltage and inversely proportio-nal to the resistance of this circuit. Mathematically:

where I is Intensity in Amperes (A), V is Voltage in Volts (V) and R is Resistance in Ohms (Ω).Using this expression you will be able to calculate one of the electric quantities in a particu-lar circuit knowing the value of the other two.

Figure 18. Georg Simon Ohm V=I·R

Figure 19. Ohm’s Law Triangle

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Video (Ohm’s Law):

Exercise

72. An automobile headlight with a resistance of 30Ω is wired to a 12 V battery. What is the current through the circuit?

73. A lamp draws a current of 0.5 A when it is connected to a 120 V source. What is the resistance of the lamp?

74. A motor with an operating resistance of 32Ω is connected to a voltage source. The current in the circuit is 3.8 A. What is the voltage of the source?

75. A 12 V battery is connected to a device and 24 mA of current flows through it. If the device obeys Ohm’s law, how much current will flow when a 24 V battery is used?

76. The current in a boom box is 0.75 A. If the resistance of the boom box is 8Ω, how many D-cell batteries placed in series will the stereo need to work? (D-cell batteries are 1.5 V each)

Figure 20. Ohm’s Law – SparkFun Electronics

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6. CONVERTING ELECTRICITY: ELECTRIC MACHINES

Electricity is a form of energy with many advantages that make its use attractive: it is possible to instantaneously transport it from one place to another, in a silent way; it is safer than other sources of energy; its impact on the environment in the place of use is almost zero.For this reason, many machines we find in our daily life are electric machines. An electric

machine is a device that uses electricity for its operation, converting it to get a certain effect that could be motion, light, heat or sound. One example of electric machine is an electric car. In an electric car, the energy comes from an internal battery that must be charged. This energy is transformed in the engine into the motion of the whe-els. This makes the electric car a great option to reduce pollution in big cities, as it emits no exhausts in his operation.

In the case of an electric car, we can find the following energy transformations

ELECTRIC ENERGYKINETIC ENERGY

(motion)

LIGHT

Exercise

77. In the following picture you can see a dynamo torch. If you ever used one you know how it works. If not, do a research on the Internet. Then complete the diagram of energy transformation that take place during its operation.

78. Write down the name of three electric machines you can find at home. Draw the energy transformation diagram.

Figure 21. Electric car charging battery

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REVISION EXERCISES

1. Find out the sign of the charge of the following ions (electrically charged atoms):

a) Chlorine atom with 18 electrons.

b) Sodium atom with 10 electrons.

c) Carbon atom with 10 electrons.

What happens if ion a) and ion c) meet each other.

2. Determine the electrical force of attraction between two balloons with separate charges of +3.5 · 10-8 C and -2.9 · 10-8 C when separated a distance of 0.65 m.

3. Determine the electrical force of attraction between two balloons that are charged with the opposite type of charge but the same quantity of charge. The charge on the balloons is 6.0 · 10-7 C and they are separated by a distance of 0.50 m.

4. Joan has rubbed a balloon with wool to give it a charge of -1.0 · 10-6 C. She then acquires a plastic golf tube with a charge of +4.0 · 10-6 C localized at a given posi-tion. She holds the location of charge on the plastic golf tube a distance of 50.0 cm above the balloon. Determine the electrical force of attraction between the golf tube and the balloon.

5. A balloon with a charge of 4.0 µC is held a distance of 0.70 m from a second ba-lloon having the same charge. Calculate the magnitude of the repulsive force.

6. An electric heater draws 3.5 A from a 110 V source. What is the resistance of the heating element?

7. If 750 µA is flowing through 11 kΏ of resistance, what is the voltage drop across the resistor?

8. Approximately how many milliamperes (mA) of current flow through a circuit with a 40 V source and 6.8 kΏ of resistance?

9. Identify the elements of the following circuit. What is the current flowing through it. Use an arrow to indicate the direction of the current (theoretical)?

6v

12 Ώ

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10. What is the total resistance of the following circuit?

500 Ώ

500 Ώ 500 Ώ

11. Complete the diagram of energy transformation that take place during the operation of the following device:

12. Identify the elements in the following circuits and explain their operation:

A.

B.