M32_KNIG7655_00_ITG_CH32

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1、CHAPTER32TheMagneticFieldRecommendedclassdays:4BackgroundInformationResearchhasfoundthatmorethan50%ofatypicalclassofstudentsbeginstheirstudybelievingthat•Apositivelychargedrodheldnearthecenterofapivotedbarmagnetcausesthemagnettorotate,withthepositivechargerepellingthenorthpoleandattractingthesouthpo

2、le.•Ifoneendofabarmagnetattractsapaperclip,theoppositeendwillrepelthepaperclip.Inadditiontothinkingthatelectricchargesandmagnetpolesaremore-or-lessequivalent,studentstendtouseelectricandmagneticfieldsinterchangeably.Thesebeliefsarelittlechangedbyconventionalinstruction.Formoststudents,theirexperienc

3、eofmagnetismextendslittlebeyondtheuseofrefrigeratormagnets.Virtuallyallschoolchildrenhaveusedamagnettopickupsmallsteelobjects,butthehighpercentagethatexpectoneendofamagnettorepeltheobjectsuggeststhattheseexperienceshavebeeninfrequent.Informalsurveysfindthatmanystudentshaveneverseenorexperiencedthere

4、pulsiveforcebetweentwomagnets.And,notsurprisingly,fewstudentsarefamiliarwithelectromagnets.Thepresentationofmagnetismusuallybeginsbyremindingstudentsthattheyarefamiliarwithrefrigeratormagnetsandperhapsotherpermanentmagnets,thenswitchesimmediatelytothedevelopmentofatheoryofelectromagnetism.Thisisacla

5、ssiccaseofbait-and-switch,withfewtextsevermakinganyconnectionbetweenelectromagnetismandpermanentmagnets.Few,ifany,32-1conventionaltextbookseveranswerthemostobviousquestionthatastudentmighthave,namely,“Howdoesthemagnetsticktotherefrigerator?”Thisisthemagneticequivalentof“Howdoesachargedcombpickuppiec

6、esofpaper?”StudentLearningObjectives•Toacquirefamiliaritywithbasicmagneticphenomena.•Todevelopadipolemodelofmagnetism,analogoustothechargemodelofelectricity,thatallowsstudentstounderstandandreasonaboutbasicmagneticphenomena.•Tolearnthemagneticfieldsduetocurrentsinwires,loops,andsolenoids.•Tostudythe

7、motionofchargedparticlesinmagneticfields.•Tounderstandthemagneticforcesandtorquesonwiresandcurrentloops.•Topresentasimpleatomic-levelmodelofferromagnetism.•Toconnectthetheoryofelectromagnetismtothephe