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
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