M33_KNIG9404_ISM_C33.pdf

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1、33ELECTROMAGNETICINDUCTIONConceptualQuestions33.1.Theinducedcurrentwillbecounterclockwise(ccw).Asthebarmovesupwardthroughtheconstant-magnetic-fieldregion,theareaoftheloopdecreases,sothefluxthroughtheloopdecreases.ByLenz’sLaw,anyinducedcurrentwilltendtoopposethisdecrease.Accwcurrentwillcrea

2、teastrongermagneticfieldinsidetheloop,tendingtoincreasetheflux.33.2.Youneedtopushagainstarepulsiveforce.Initsinitialposition,theloopencirclesessentiallynomagneticflux,whereasoncetheloopispositionedbetweenthepolesofthemagnet,magneticfluxwillpassthroughtheloop.Lenz’sLawtellsusthatthecurrentf

3、lowsinthedirectionrequiredtoopposeachangeinflux,sothecurrentwillflowinthedirectionrequiredtocreatearepulsiveforceonthecopperwire.Thecurrentinducedintheloopisthereforeinthedirectionshown(intothepageontheleftsideofthecopperloop).Themagneticpolesoftheinducedcurrentlooparealsoshowninthediagram

4、.Theresultingmagneticforceontheloopistotheright.Notethatifthemagneticpoleswerereversed,theinducedcurrentwouldreverseaswellsothattheresultingforcewouldstillbetotheright.33.3.Yes,thereisanetupwardforce.Lenz’sLawtellsusthatacurrentwillbeinducedinthelooptoopposethedchangeinmagneticflux.Thenetf

5、orcewillbeupwardbecausetheupperloopsegmenttraversesthefieldBwhereasthelowerloopsegmentdoesnot(thetwosidesegmentsproduceforcesofequalmagnitudebutinoppositedirections).Weknowtheforcemustbeupwardbecause,byLenz’sLaw,itmustopposetheforceduetogravitythatiscausingthechangeinflux.©Copyright2013Pea

6、rsonEducation,Inc.Allrightsreserved.Thismaterialisprotectedunderallcopyrightlawsastheycurrentlyexist.Noportionofthismaterialmaybereproduced,inanyformorbyanymeans,withoutpermissioninwritingfromthepublisher.33-133-2Chapter3333.4.(a)Clockwise.Theinducedmagneticfieldisintothepageandbytheright-

7、handruletheinducedcurrentisclockwise.(b)Nocurrent.Achangingmagneticfluxisnecessarytoinduceacurrent.(c)Counterclockwise.Theinducedmagneticfieldisoutofthepage.33.5.(a)Nocurrent.Nomagneticfluxischanging,sonomagneticfieldisinduced.(b)Clockwise.Anincreasingcounterc