雨课堂学堂在线学堂云University PhysicsElectricity and Magnetism(云南大学)单元测试考核答案

第1题Lifewillnotbedifferentiftheelectronwerepositivelychargedandtheprotonwerenegativelycharged.A正确B错误第2题Aglassobjectispositivelychargedbyrubbingitwithasilkcloth.Therefore,thepositivechargeswerecreatedontheglassobjectintherubbingprocess.A正确B错误第3题Threeobjectsarebroughtclosetoeachother,twoatatime.WhenobjectsAandBarebroughttogether,theyrepel.WhenobjectsBandCarebroughttogether,theyalsorepel.Whichofthefollowingaretrue?AObjectsAandCpossesschargesofoppositesign.BAllthreeobjectspossesschargesofthesamesign.COneobjectisneutral.DAdditionalexperimentsmustbeperformedtodeterminethesignsofthecharges.第4题Threeobjectsarebroughtclosetooneanother,twoatatime.WhenobjectsAandBarebroughttogether,theyattract.WhenobjectsBandCarebroughttogether,theyrepel.Whichofthefollowingarenecessarilytrue?AObjectsAandCpossesschargesofthesamesign.BObjectsAandCpossesschargesofoppositesign.CAllthreeobjectspossesschargesofthesamesign.DOneobjectisneutral.EAdditionalexperimentsmustbeperformedtodetermineinformationaboutthechargesontheobjects.正确答案：E第1题ABCD第2题ABCDELecture3ElectricFields--作业第1题Theexistenceofanelectricfieldisapropertyofthesourcecharge.第2题ABC第3题Anobjectwithnegativechargeisplacedinaregionofspacewheretheelectricfieldisdirectedverticallyupward.Whatisthedirectionoftheelectricforceexertedonthischarge?AItisup.BItisdown.CThereisnoforce.DTheforcecanbeinanydirection.Lecture4EvaluationofElectricFields（I）--作业第1题ABCDE第2题A40-µCchargeispositionedonthexaxisatx=4.0cm.Whereshoulda–60-µCchargebeplacedtoproduceanetelectricfieldofzeroattheorigin?A–5.3cmB5.7cmC4.9cmD–6.0cmE+6.0cmLecture5EvaluationofElectricField(II)--作业第1题ABCDE第2题ABCD第3题ABCDE第4题ABCDLecture6ElectricFieldLines--作业第1题ABCDELecture7ElectricFlux--作业第1题ABCDE第2题ABCDE第3题ABCDELecture8Gauss’sLaw--作业第1题Supposeapointchargeislocatedatthecenterofasphericalsurface.Theelectricfieldatthesurfaceofthesphereandthetotalfluxthroughthespherearedetermined.Nowtheradiusofthesphereishalved.Whathappenstothefluxthroughthesphereandthemagnitudeoftheelectricfieldatthesurfaceofthesphere?AThefluxandfieldbothincrease.BThefluxandfieldbothdecrease.CThefluxremainsthesame,andthefieldincreases.DThefluxdecreases,andthefieldremainsthesame.第2题Ifthenetfluxthroughagaussiansurfaceiszero,thefollowingfourstatementscouldbetrue.Whichofthestatementsmustbetrue?ATherearenochargesinsidethesurface.BThenetchargeinsidethesurfaceiszero.CTheelectricfieldiszeroeverywhereonthesurface.第3题TheelectricfieldatanypointonaGaussiansurfaceisproducedbythenetchargeenclosedbytheGaussiansurface.Lecture9ApplicationofGauss’sLaw--作业第1题ABCDE第2题ABCDE第3题ABCDE第4题Acubicalgaussiansurfacesurroundsalong,straight,chargedfilamentthatpassesperpendicularlythroughtwooppositefaces.Nootherchargesarenearby.Overhowmanyofthecube’sfacesistheelectricfieldzero?A0B2C4D6第5题Acubicalgaussiansurfacesurroundsalong,straight,chargedfilamentthatpassesperpendicularlythroughtwooppositefaces.Nootherchargesarenearby.Throughhowmanyofthecube’sfacesistheelectricfluxzero?A0B2C4D6Lecture10ElectricPotential--作业第1题ABC第2题ABC第3题ABC第4题ABC第5题ABCDE第6题Theelectricpotentialatanypointinspaceisdependentonthechargelocatedatthispoint.Lecture11EvaluationofElectricPotential--作业第1题Identical4.0-µCchargesareplacedontheyaxisaty=±4.0m.PointAisonthexaxisatx=+3.0m.DeterminetheelectricpotentialofpointA(relativetozeroattheorigin).A–4.5kVB–2.7kVC–1.8kVD–3.6kVE–14kV第2题AchargeQisuniformlydistributedalongthexaxisfromx=atox=b.IfQ=45nC,a=–3.0m,andb=2.0m,whatistheelectricpotential(relativetozeroatinfinity)atthepoint,x=8.0m,onthexaxis?A71VB60VC49VD82VE150V第3题ABCDE第4题ABCDE第5题ABCDELecture12FindingEfromV--作业第1题Inacertainregionofspace,theelectricpotentialiszeroeverywherealongthexaxis.Fromthisinformation,youcanconcludethatthexcomponentoftheelectricfieldinthisregionis:Azero.Binthepositivexdirection.Cinthenegativexdirection.第2题Inacertainregionofspace,theelectricpotentialis+2Veverywherealongthexaxis.Fromthisinformation,youcanconcludethatthexcomponentoftheelectricfieldinthisregionis:Azero.Binthepositivexdirection.Cinthenegativexdirection.第3题Inacertainregionofspace,theelectricfieldiszero.Fromthisfact,whatcanyouconcludeabouttheelectricpotentialinthisregion?AItiszero.BItdoesnotvarywithposition.CItispositive.DItisnegative.ENoneofthoseanswersisnecessarilytrue.第4题ABCDELecture13Propertiesofaconductorinelectrostaticequilibrium（I）--作业第1题TheelectricpotentialinsideachargedsolidsphericalconductorinequilibriumAisalwayszero.Bisconstantandequaltoitsvalueatthesurface.Cdecreasesfromitsvalueatthesurfacetoavalueofzeroatthecenter.Dincreasesfromitsvalueatthesurfacetoavalueatthecenterthatisamultipleofthepotentialatthesurface第2题ABCDELecture14Propertiesofaconductorinelectrostaticequilibrium(II)--作业第1题Anastronautisinanall-metalchamberoutsidethespacestationwhenasolarstormresultsinthedepositofalargepositivechargeonthestation.Whichstatementiscorrect?ATheastronautmustabandonthechamberimmediatelytoavoidbeingelectrocuted.BTheastronautwillbesafeonlyifsheiswearingaspacesuitmadeofnon-conductingmaterials.CTheastronautdoesnotneedtoworry:thechargewillremainontheoutsidesurface.DTheastronautmustabandonthechamberiftheelectricfieldontheoutsidesurfacebecomesgreaterthanthebreakdownfieldofair.第2题Asmallmetalsphereissuspendedfromtheconductingcoverofaconductingmetalicebucketbyanon-conductingthread.Thesphereisgivenanegativechargebeforethecoverisplacedonthebucket.Thebucketistiltedbymeansofanon-conductingmaterialsothatthechargedspheretouchestheinsideofthebucket.Whichstatementiscorrect?AThenegativechargeremainsonthemetalsphere.BThenegativechargespreadsovertheoutsidesurfaceofthebucketandcover.CThenegativechargespreadsovertheinsidesurfaceofthebucketandcover.DThenegativechargespreadsequallyovertheinsideandoutsidesurfacesofthebucketandcover.第3题ABCDLecture15Dielectrics--作业第1题Dielectricsalwaysreducetheelectricfieldtobezeroduetopolarization.第2题Electricdipoleswilltendtoalignwiththeelectricfieldundertheactionofthetorqueexertedbythefield.Lecture16Capacitor&Capacitance--作业第1题Whathappenstothemagnitudeofthechargeoneachplateofacapacitorifthepotentialdifferencebetweentheconductorsisdoubled?AItbecomesfourtimeslarger.BItbecomestwotimeslarger.CItisunchanged.DItbecomesone-halfaslarge.EItbecomesone-fourthaslarge.第2题ABCDE第3题ABCDE第4题ABCDE第5题FromthedefinitionofcapacitanceC=Q/ΔV,itfollowsthatanunchargedcapacitorhasacapacitanceofzero.第6题Asdescribedbythedefinitionofcapacitance,thepotentialdifferenceacrossanunchargedcapacitoriszero.Lecture17Capacitorswithdielectrics--作业第1题ABCDE第2题ABCDE第3题ABCDE第4题ABCDE第5题Ifthreeunequalcapacitors,initiallyuncharged,areconnectedinseriesacrossabattery,whichofthefollowingstatementsistrue?ATheequivalentcapacitanceisgreaterthananyoftheindividualcapacitances.BThelargestvoltageappearsacrossthesmallestcapacitance.CThelargestvoltageappearsacrossthelargestcapacitance.DThecapacitorwiththelargestcapacitancehasthegreatestcharge.EThecapacitorwiththesmallestcapacitancehasthesmallestcharge.第6题Abatteryisattachedtoseveraldifferentcapacitorsconnectedinparallel.Whichofthefollowingstatementsistrue?AAllcapacitorshavethesamecharge,andtheequivalentcapacitanceisgreaterthanthecapacitanceofanyofthecapacitorsinthegroup.BThecapacitorwiththelargestcapacitancecarriesthesmallestcharge.CThepotentialdifferenceacrosseachcapacitoristhesame,andtheequivalentcapacitanceisgreaterthananyofthecapacitorsinthegroup.DThecapacitorwiththesmallestcapacitancecarriesthelargestcharge.EThepotentialdifferencesacrossthecapacitorsarethesameonlyifthecapacitancesarethesame.Lecture18Energystoredinacapacitor--作业第1题Aparallel-platecapacitorisconnectedtoabattery.Whathappenstothestoredenergyiftheplateseparationisdoubledwhilethecapacitorremainsconnectedtothebattery?AItremainsthesame.BItisdoubled.CItdecreasesbyafactorof2.DItdecreasesbyafactorof4.EItincreasesbyafactorof4.第2题Ifthepotentialdifferenceacrossacapacitorisdoubled,whathappenstotheenergystored?AItbecomesfourtimeslarger.BItbecomestwotimeslarger.CItisunchanged.DItbecomesone-halfaslargeEItbecomesone-fourthaslarge.第3题Aparallel-platecapacitorischargedandthenisdisconnectedfromthebattery.Bywhatfactordoesthestoredenergychangewhentheplateseparationisthendoubled?AItbecomesfourtimeslarger.BItbecomestwotimeslarger.CItstaysthesame.DItbecomesone-halfaslarge.EItbecomesone-fourthaslarge.Lecture20Current&CurrentDensity--作业第1题ABCD第2题ToincreasethecurrentdensityinawireoflengthlanddiameterD,youcanAdecreasethepotentialdifferencebetweenthetwoendsofthewireBincreasethepotentialdifferencebetweenthetwoendsofthewire.Cdecreasethemagnitudeoftheelectricfieldinthewire.Dheatthewiretoahighertemperature.Ecombineboth(2)and(4).Lecture22MagneticFields--作业第1题Onereasonwhyweknowthatmagneticfieldsarenotthesameaselectricfieldsisbecausetheforceexertedonacharge+qAisinoppositedirectionsinelectricandmagneticfields.Bisinthesamedirectioninelectricandmagneticfields.Cisparalleltoamagneticfieldandperpendiculartoanelectricfield.Disparalleltoanelectricfieldandperpendiculartoamagneticfield.Eiszeroinbothifthechargeisnotmoving.第2题Achargedparticle(mass=M,charge=Q>0)movesinaregionofspacewherethemagneticfieldhasaconstantmagnitudeofBandadownwarddirection.WhatisthemagneticforceontheparticleataninstantwhenitismovinghorizontallytowardthenorthwithaspeedV?AQVBtowardtheeastBZeroCQVBtowardthewestDQVBupwardEQVBtowardthesouth第3题Anelectronmovesintheplaneofthispapertowardthetopofthepage.Amagneticfieldisalsointheplaneofthepageanddirectedtowardtheright.Whatisthedirectionofthemagneticforceontheelectron?AtowardthetopofthepageBtowardthebottomofthepageCupwardoutofthepageDdownwardintothepage第4题Aspatiallyuniformmagneticfieldcannotexertamagneticforceonaparticleinwhichofthefollowingcircumstances?Theremaybemorethanonecorrectstatement.ATheparticleischarged.BTheparticlemovesperpendiculartothemagneticfield.CTheparticlemovesparalleltothemagneticfield.DThemagnitudeofthemagneticfieldchangeswithtime.ETheparticleisatrest.正确答案：CE第5题ABCDELecture23ChargedParticleinaMagneticField--作业第1题ABCDE第2题Achargedparticleismovingperpendiculartoamagneticfieldinacirclewitharadiusr.Anidenticalparticleentersthefield,withvperpendiculartoB,butwithahigherspeedthanthefirstparticle.Comparedwiththeradiusofthecircleforthefirstparticle,theradiusofthecircularpathforthesecondparticleis:Asmaller.Blarger.Cequalinsize.第3题Achargedparticleismovingperpendiculartoamagneticfieldinacirclewitharadiusr.Themagnitudeofthemagneticfieldisincreased.Comparetheradiusofthenewcircularpathofthefirstparticlewiththeradiusofitsinitialpathis:AsmallerBlargerCequalinsize第4题Bertsaysthatachargedparticleinavacuumcantravelinahelixonlyifauniformelectricfieldandauniformmagneticfieldarebothpresentandbothparalleltotheaxisofthehelix.Stuartsaysthatonlyamagneticfieldwithacomponentparalleltotheaxisofthehelixisneeded.Whichone,ifeither,iscorrect,andwhy?ABert,becausethechargedparticle’svelocitycanhaveaverticalcomponentonlyifanelectricfieldintheverticaldirectionispresent.BStuart,becauseacomponentofvelocityintheverticaldirectionisnotchangedbyaverticalcomponentofamagneticfield.CBert,becauseacomponentofvelocityintheverticaldirectionischangedbyaverticalcomponentofamagneticfield.DStuart,becauseanelectricfieldintheverticaldirectionwouldcausetheparticletocometoacompletestop.ENeither,becauseparticlescannotmoveinhelicalpathsinthepresenceofmagneticandelectricfields.Lecture24MagneticForceonaCurrent—CarryingConductor--作业第1题Awirecarriescurrentintheplaneofthispapertowardthetopofthepage.Thewireexperiencesamagneticforcetowardtherightedgeofthepage.Thedirectionofthemagneticfieldcausingthisforceis:Aintheplaneofthepageandtowardtheleftedge.Bintheplaneofthepageandtowardthebottomedge.Cupwardoutofthepage.Ddownwardintothepage.第2题ABCDE第3题ABCDE第4题ABCDE第5题ABCDE第6题ABCD第7题ABCDLecture25SourcesofaMagneticField--作业第1题ABCD第2题Atapointinspacewherethemagneticfieldismeasured,themagneticfieldproducedbyacurrentelementApointsradiallyawayinthedirectionfromthecurrentelementtothepointinspace.Bpointsradiallyinthedirectionfromthepointinspacetowardsthecurrentelement.Cpointsinadirectionparalleltothecurrentelement.Dpointsinadirectionparalleltobutoppositeindirectiontothecurrentelement.Epointsinadirectionthatisperpendiculartothecurrentelementandperpendiculartotheradialdirection.正确答案：ELecture26CalculationofamagneticfieldbyapplyingtheBiot-SavartLaw--作业第1题ABCDE第2题ABCDE第3题ABCDE第4题ABCDE第5题ABCDE正确答案：E第6题Aloosespiralspringcarryingnocurrentishungfromaceiling.Whenaswitchisthrownsothatacurrentexistsinthespring,thecoils:Amoveclosertogether.Bmovefartherapart.Cdonotmoveatall.Lecture27Ampere’sLaw--作业第1题ABCD第2题Byusingacompasstomeasurethemagneticfielddirectionatvariouspointsadjacenttoalongstraightwire,youcanshowthatthewire’smagneticfieldlinesareAstraightlinesinspacethatgofromonemagneticchargetoanother.Bstraightlinesinspacethatareparalleltothewire.Cstraightlinesinspacethatareperpendiculartothewire.Dcirclesthathavetheircentersonthewireandlieinplanesperpendiculartothewire.Ecirclesthathavethewirelyingalongadiameterofthecircle.第3题ABCDLecture28ApplicationofAmpere’sLaw--作业第1题Considerasolenoidthatisverylongcomparedwithitsradius.Ofthefollowingchoices,whatisthemosteffectivewaytoincreasethemagneticfieldintheinteriorofthesolenoid?Adoubleitslength,keepingthenumberofturnsperunitlengthconstantBreduceitsradiusbyhalf,keepingthenumberofturnsperunitlengthconstantCoverwraptheentiresolenoidwithanadditionallayerofcurrent-carryingwire第2题ABCDE第3题ABCDE第4题ABCDE正确答案：E第5题Alongstraightwire(diameter=2.0mm)carriesacurrentof25A.Whatisthemagnitudeofthemagneticfield0.50mmfromtheaxisofthewire?A5.0mTB10mTC0.63mTD2.5mTE0.01mT第6题Alongstraightwire(diameter=2.0mm)carriesacurrentof40A.Whatisthemagnitudeofthemagneticfield1.5mmfromtheaxisofthewire?A3.0mTB12mTC5.3mTD7.4mTE8.0mT第7题Whenthenumberofturnsinasolenoidanditslengtharebothdoubled,theratioofthemagnitudeofthenewmagneticfieldinsidetothemagnitudeoftheoriginalmagneticfieldinsideis:A0.25B0.50C1D2E4Lecture29Gauss’sLawinMagnetism--作业第1题ABCDE第2题Auniformmagneticfieldisdirectedalongthexaxis.orwhatorientationofaflat,rectangularcoilistheluxthroughtherectangleamaximum?Aisamaximuminthexyplane.BItisamaximuminthexzlane.CItisamaximumintheyzplane.DThefluxasthesamenonzerovalueforalltheseorientations.EThefluxiszeroinallcases.Lecture30Originofthemagneticeffectofmaterials--作业第1题ABCDLecture31Magnetization--作业第1题Themagneticdipolewilltendtoalignwiththedirectionoftheexternalfieldduetotheactionofthenettorque,sothatthesystemhastheminimumvalueofthepotentialenergy.Lecture32MagneticMaterials--作业第1题Whichofthefollowingtype(s)ofmaterialsis(are)repelledwhenamagnetisbroughtnearby?AParamagneticBDiamagneticCFerromagneticDparamagneticandferromagneticEparamagnetic,ferromagnetic,anddiamagnetic第2题WhenaferromagneticmaterialthathasbeenmagnetizedisbroughttoatemperaturegreaterthantheCurietemperature,whathappenstoitsresidualmagnetism.ANothinghappenstotheresidualmagnetism.BTheresidualmagnetismdisappears.CTheresidualmagnetismreachesit’shighestvalue.DAllthemagneticdomainscausingmagnetismbecomeasingledomain.EThematerialofthemagnetmeltscausingcurrentsthataremagnetic.第3题Ontheaverage,inaferromagneticdomainpermanentatomicmagneticmomentsarealigned_____tooneanother.AantiparallelBparallelCperpendicularDalternatelyparallelandantiparallelErandomlyrelativeLecture33Faraday’sLaw--作业第1题ABCDE第2题ABCDE第3题Acircularloopofwireisheldinauniformmagneticfield,withtheplaneoftheloopperpendiculartothefieldlines.Whichofthefollowingwillnotcauseacurrenttobeinducedintheloop?AcrushingtheloopBrotatingtheloopaboutanaxisperpendiculartothefieldlinesCkeepingtheorientationoftheloopfixedandmovingitalongthefieldlinesDpullingtheloopoutofthefieldLecture34MotionalEMF--作业第1题ABCDE正确答案：CD第2题ABCDE正确答案：BD第3题ABCDE正确答案：E第4题AcurrentmaybeinducedinacoilbyAmovingoneendofabarmagnetthroughthecoil.Bmovingthecoiltowardoneendofthebarmagnet.Choldingthecoilnearasecondcoilwhiletheelectriccurrentinthesecondcoilisincreasing.Dalloftheabove.Enoneoftheabove.第5题AninducedemfisproducedinAaclosedloopofwirewhenitremainsatrestinanonuniformstaticmagneticfield.Baclosedloopofwirewhenitremainsatrestinauniformstaticmagneticfield.Caclosedloopofwiremovingatconstantvelocityinanonuniformstaticmagneticfield.Dalloftheabove.Eonly2and3above.Lecture35InducedElectricField--作业第1题Theelectricfieldinducedbychangingmagneticfieldisnonconservative,whiletheelectricfieldproducedbythestationaryelectricchargesisconservative.Lecture36Generators--作业第1题InanACgenerator,acoilwithNturnsofwirespinsinamagneticfield.Ofthefollowingchoices,whichdoesnotcauseanincreaseintheemfgeneratedinthecoil?AreplacingthecoilwirewithoneoflowerresistanceBspinningthecoilfasterCincreasingthemagneticfieldDincreasingthenumberofturnsofwireonthecoil第2题ThedifferencebetweenaDCandanACgeneratoristhatATheDCgeneratorhasoneunbrokenslipring.BTheACgeneratorhasoneunbrokenslipring.CTheDCgeneratorhasoneslipringsplitintwohalves.DTheACgeneratorhasoneslipringsplitintwohalves.ETheDCgeneratorhastwounbrokensliprings.Lecture37Inductance--作业第1题Twosolenoids,AandB,arewoundusingequallengthsofthesamekindofwire.Thelengthoftheaxisofeachsolenoidislargecomparedwithitsdiameter.TheaxiallengthofAistwiceaslargeasthatofB,andAhastwiceasmanyturnsasB.WhatistheratiooftheinductanceofsolenoidAtothatofsolenoidB?A4B2C1D1/2E1/4第2题ABC第3题ABC第4题ABC第5题AninductorproducesabackemfinaDCseriesRLcircuitwhenaswitchconnectingthebatterytothecircuitisclosed.WecanexplainthisbyALenz’slaw.Bincreasingmagneticfluxwithinthecoilsoftheinductor.Cincreasingcurrentinthecoilsoftheinductor.Dalloftheabove.Eonly(1)and(3)above.第6题Acoilwithzeroresistancehasitsendslabeledaandb.Thepotentialataishigherthanatb.Which