ch9 Electromagnetic induction

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1、ElectromagneticInductionChapter9Chapter9ElectromagneticInduction9-1Faraday’sLawofInduction9-2MotionalEmf9-3InducedEmfandInducedElectricField9-4Self-Induction9-5EnergyinaMagneticField9-6MutualInduction9-1Faraday’sLawofInductionInducedEmfandMagneticFluxWhentheswitchintheprimarycircui

2、tissuddenlyclosedoropened,currentscanbecreatedinthesecondarycircuit.Itisthechangeinmagneticfieldthatcreatesthecurrent,whichiscalledaninducedcurrent.Morebasicthanthecurrentthatflowsistheinducedemfthatcausesit.Thecurrentisaresultofanemfinducedbyachangingmagneticfield,whetherornotthe

3、reisapathforcurrenttoflow.Anemfwasinducedinthecoilwhenabarmagnetwaspushedinandoutofit.Emfsofoppositesignswerecreatedbymotioninoppositedirections,andtheemfswerealsoreversedbyreversingpoles.Thesameresultsproducedwhenthecoilwasmovedratherthanthemagnetitistherelativemotionthatisimport

4、ant.Thefasterthemotion,thegreatertheemf,andtherewasnoemfwhenthemagnetwasstationaryrelativetothecoil.iMotionofmagnetiMotionofmagnetFaraday’slawofinduction:Theemfinducedinaloopofwireisproportionaltotherateofchangeofmagneticfluxthroughthecoil.Lenz’sLawLenz’slawstatesthatthedirectionof

5、aninducedcurrentissuchthatitsownmagneticfieldopposesthechangeinoriginalmagneticfluxthatinducedthecurrent.FieldduetomagnetonlyMotionSNInducedfieldonlyMotioniSN①determinethedirectionofinitialmagneticfield②determinethechangeofmagneticfluxintheloop③fromLenz’slawtodeterminethedirectiono

6、finducedcurrentandareopposite.ExampleUsingLenz’slawtodeterminethedirectionofinducedcurrentandareinthesamedirectionCheckpoint1Faraday’sLawofInductionWecannowwriteFaraday’slawofinductionmathematicallywiththeequation(Faraday’slaw)iThreemeanstochangethemagneticfluxthroughacoil:Checkpoi

7、nt2Minussignexpressesthedirectionof.DiscussionThedistributionofFluxmeterInducedcurrentInducedchargeForanN-turncoil:(totalfluxorfluxlinkage)FromR,qExample9-1........AxisiiCSThelongsolenoidShas220turns/cmandcarriesacurrenti=1.5A;itsdiameterDis3.2cm.Atitscenterweplacea130-tur

8、nclose-packedcoilofdiamete