s=ut+ at 21 -2 v 2=u 2+as

P=2l+2w

P= w -t

G R A D E B O O S T E RG R A D E B O O S T E R

I G C S E P H Y S I C SI G C S E P H Y S I C S

MAGNETISM AND ELECTROMAGNETISM 6

EDEXCEL

Unit 6 Magnetism and Electromagnetism

作者 | Bettina Chan

出版 | Lab Edu Limited

版權為 Lab Edu Limited 所擁有

I GCSE PHYSICS - UNIT 6MAGNETISM AND ELECTROMAGNETISM

EdexcelIGCSE Physics Grade Booster

01 02

AFTER-CLASS EXERCISE

LESSON FLOW

1. MagnetismandElectromagnetism

2. ElectricMotorsandElectromagneticInduction

1. Coverallkeypointsinthespecification

2. Gooversamplequestions

3. Masterexam-typequestions

CONTENT

P.03-05Magnetism and Electromagnetism

Electric Motors and Electromagnetic Induction

Unit 6 Questions

P.06-10

P.11-14

LEARNING OBJECTIVES

Question Type

1 Knowledge-based

2 Experimental

3 Calculation

4 Experimental

5 Knowledge-based

6 Knowledge-based

7 Knowledge-based

8 Knowledge-based

9 DiagramDrawing

10 Knowledge-based

03 04

Magnetism and ElectromagnetismMagnetsNorthpoleSouthpole

• S…………………polesrepel

• O…………………polesattract

Magnetic field

Magnetic field:volumeofspacewherewecandetectmagnetism

Magnetic field lines:

1. Theshapeofthemagnetismfield

2. Thedirectionofthemagneticforce

3. Thestrengthofthemagneticfield

Strongermagneticfield—fieldlinesareclosetogether

Weakmagneticfield—fieldlinesarewidelyspaced

Investigate the Magnetic Field Patterns of Bar Magent

1. Placeabarmagnetbetweenbooksandplaceasheetofpaperorthincardoverit

2. Sprinkleironfillingsonthepaperabovethemagnet

3. Tapthepapergently

4. Ironfillingswillmigratetoshowthemagneticfieldpattern

OR

1. Placeamagnetbaronpieceofpaper

2. Placealargenumberofsmallcompassesonthepapernearthemagnet

3. Lookatthepatternshownbytheneedlesofthecompasses

Repeattheexperimentusingtwobarmagnets,placingthemabout5cmapart

Induce magnetism

S………………… materials (e.g. iron)Whenplacedinsideamagneticfield,itbecomesmagnetTemporaryanddisappearswhenitisremovedfromamagneticfield

H………………… materials (e.g. steel)Retainsomemagnetismafterthemagnetisremoved

Electromagnetism

Amagneticfieldiscreatedaroundawirewhenthereiscurrent.

The strength of the field around the solenoid can be increased by:

1. Increasingthecurrentinthesolenoid.

2. Increasingthenumberofturnsperunitlengthonthesolenoid.

3. Wrappingthesolenoidaroundamagneticallysoftcore.

S SN S

05 06

Magnetically hard coreretaininducedmagneticfield

***copperisnotmagnetic***

Right hand rule:

The strength of the magnetic field around a current-carrying wire can be

increased by:

1. Increasingthecurrentinthewire

2. Wrappingthewireintoacoilorsolenoid

Electric Motors and Electromagnetic InductionOverlapping Magnetic Fields

Whentwomagnetsarepositionedclosetoeachother,themagneticfieldsoverlapand

affecteachother.

Whenthedirectionofcurrentisnotparalleltothedirectionofthemagneticfield,a

forceisinduced.

Whendirectionofcurrentisparalleltodirectionofmagneticfield,noforceisinduced

Fleming’s left-hand rule

N S

thumbgivesdirectionofmotionorforce

firstfingergivesdirectionoffield(NtoS)

secondfingergivesdirectionofcurrentinwire

THUMB

FIRST

SECOND

07 08

The Moving-coil LoudspeakerUsesthemotoreffecttotransferelectricalenergytosoundenergy

1. Electriccurrentsfromasourcepassthroughthecoilsofaspeaker.

2. Thesecurrents,whichrepresentsounds,alwayschangesinsizeanddirection

3. The fieldsof thecoilandthepermanentmagnet thencreatemagnetic field

patternswhichalsochangeinstrengthanddirection.

4. Thesefieldsinturnapplyrapidlychangingforcestothewiresofthecoil,which

causethespeakerconetovibrate.

5. Thevibrationsmakethesoundwaves.

Electric Motor

Toincreasetherateatwhichthemotorturnswecan:

• …………………thenumberofturnsorloopsofwire,makingacoil

• …………………thestrengthofthemagneticfield

• …………………thecurrentintheloopofwire

Electromagnetic induction

Thesizeoftheinducedvoltage(andcurrent)canbeincreasedby:

Thesizeofinducedcurrentcanbeincreasedby:

1. movingthemagnetmoreq…………………

2. usingas…………………magnet

3. usingacoilwithm………………….turns

S N

A

N S

A

movementofwire

inducedcurrent

09 10

The transformer

Atransformerchangesthesizeofanalternatingvoltage. Itdoesthisbyhavingdifferentnumbersofturnsontheinputandoutputsides.

Whenthere isalternatingcurrent inacoil, themagnetic fieldaround itchangescontinuously.Asthesizeofthecurrentinthecoilincreases,thefieldgrows.

Ifasecondcoilisplacednearthefirst,thisgrowingandcollapsingmagneticfieldwillpassthroughit.Thesizeanddirectionoftheinducedvoltagechangesasthevoltageappliedtothefirstcoilchanges.(Thefirstcoilisusuallycalledthep…………………coil.)Analternatingvoltageappliedacross theprimarycoil thereforeproducesanalternatingvoltageacrossthes…………………coil.Thiscombinationof twomagneticallylinkedcoilsiscalledatransformer.

Voltagesacrosseachofthecoilsislinkedasfollows:

V=voltagen=numberofturnsoncoilE.g. Atransformerhas250turnsand500turnsonitsprimarycoilandsecondarycoil

respectively.Ifanalternatingvoltageof4Visappliedacrosstheprimary,findthevoltageacrossthesecondarycoil.

Vs=

Vs=

Energy in Transformers

VpIp=VsIsInputpower=outputpower

E.g. Whenavoltageof24Va.c. isappliedacrosstheprimarycoilofastepdown

transformer,thereisacurrentof0.5Aintheprimarycoil.Calculatethecurrent

inthesecondarycoil ifthevoltageinducedacrossit is4Va.c.Assumethatthe

transformeris100%efficient.

VpIp=VsIs=VsxIsIs=

Is=

Transformer and National Grids

Thelargerthecurrent,thegreatertheamountofenergyloss.Currentinthewiresis

kepttoaminimum,theheatlossescanbereduced.ByP=IV,ifcurrentistheminimum

value,highvoltagemustbeusedtodeliverthesamepower.

softironcorelinkingthetwocoils

primarycoil,withnpturns

secondarycoil,withnsturns

alternatingoutputvoltage,

Vs

alternatinginputvoltage,

Vp~~

Vp =Vs

np

ns

Vp =Vs

np

ns

=Vs

11 12

1. Acoilofwirecarryingacurrentinamagneticfieldexperiencesaforcewhichmakes

itrotate.Thisphenomenonisusedinelectricmotors.Suggestwaystoincreasethe

turningrateofamotor.

2. Howcanastudentincreasetheinducedvoltage?

3. Calculatethenumberofturnsinthesecondarycoil.

4. Describeanexperimenttodeterminethemagneticfieldofmagnets.

5. Describewhathappenswhenalongwireisplacedbetweenthepolesofamagnet.

6. Whatismagneticfield?

7. Whatisthedefinitionofhardmaterial?

8. Whichofthefollowingobjectsisnotmadeofmagneticmaterials?

A. Ironbar

B. Steelnail

C. Copperpipe

9. Dramadiagramofauniformmagneticfieldbetweentwomagnetsbar

10. Howdoesanalternatingcurrentgenerateasoundwave?

Unit 6 Questions

Vp=600V

Np=1000Turns Ns=?

Vs=250V

13 14

Mark scheme

1. • Increasethenumberofturnsorloopsofwire,makingacoil.

• Increasethestrengthofthemagneticfield.

• Increasethecurrentintheloopofwire.

2. • Movingthemagnetmorequickly

• Usingastrongermagnet

• Usingacoilwithmoreturns

3. Vp/Vs=np/ns

ns=416.67turns

4. • Placeplottingcompassatside

• Markpositionofendofcompass

• Move-endofcompassneedletonewmarkandrepeat.

• Directionlinkedtogethertofindafieldline.

5. • Thereiscurrentinthecoil.

• Itcreatesamagneticfieldaroundthewiresofthecoil.

• Interactionoffieldwiththatofmagnets.

• Thereisaforceonthewire.

• Thisiswithreferencetothelefthandrule.

• Forceisupononesideanddownontheotherside.

6. Volumeofspacewherewecandetectmagnetism

7. Hardmaterial:Retainsomeofitsmagnetism.

8. C

9.

10. • Alternatingcurrentchangesdirection.

• Currentinthecoilproducesanalternatingmagneticfield.

• Producingforceonthecoil.

• Reversingdirectiononcurrentreversesdirectionoftheforce.

• Hencecoilvibrateswhichcausesairparticlestovibrate

N S

600=

2501000ns

s=ut+ at 21 -2 v 2=u 2+as

P=2l+2w

P= w -t

G R A D E B O O S T E RG R A D E B O O S T E R

I G C S E P H Y S I C SI G C S E P H Y S I C S

MAGNETISM AND ELECTROMAGNETISM 6

EDEXCEL