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1、CHAPTER31FundamentalsofCircuitsRecommendedclassdays:3minimum,4preferredBackgroundInformationAnextensivesummaryofresearchfindingsaboutstudents’understandingofcircuitswasgiveninthe“PhysicsEducationResearch”chapterofthisguidebook.TheprimaryreferencesareCohenetal.(
2、1983),McDermottandShaffer(1992),andShafferandMcDermott(1992).Fromtheresearch,welearnthat:•Studentsdonotdifferentiatebetweentheconceptsofcurrent,voltage,energy,andpower.Tothem,it’salljust“electricity.”Thesituationisanalogoustostudents’useoftheterm“motion”todescr
3、ibeeithervelocityoracceleration.•Studentsthinkalmostexclusivelyaboutcurrent,rarelyorneveraboutpotentialdifference.Thusthemajorityofstudents,evenafterseeingexperimentalevidencethatsuggestsotherwise,continuetobelievethatbatteriesareconstant-currentsources.•Studen
4、tscannotreasonwiththeconceptofpotentialdifference,andtheyrarelyinvokepotentialdifferencespontaneously.Whenpotentialdifferencesarise,itisalmostinvariablyinthecontextofOhm’slaw:ΔV=IR.Intheseinstances,studentsseeapotentialdifferenceasaneffectratherthanacause.Stude
5、ntsdonotuseΔ=Vloop0toreasonaboutcircuits,andmanyhavetroublefollowinganargumentthatdoesso.Theirunderstandingofpotentialdifferenceisnotsomuchamisconceptionasnoconception.•Studentsreasonlocally,notglobally.Inmostcircumstances,theydonotseethatchangingonecircuitcomp
6、onentwillaffectthevoltageandcurrentatotherpointsinthecircuit.•Studentshavenomicro/macrounderstandingofcircuits.Theydonotseeanyconnectionbetweenmacroscopicquantities,suchascurrentorresistance,andtheirpreviousstudyofcharges,forces,andfields.Tostudents,circuitsare
7、asubjectentirelyindependentofelectrostatics.31-1Theseconclusionsareperhapsnotsurprising.SurveysattheUniversityofWashingtonhavefoundthatlessthan20%ofstudentsreportevenrudimentaryexperiencewithbattery-and-bulbtypesofcircuits.I’veconfirmedthisinmyownsurveysofstude
8、nts,andI’vealsofoundthatthepercentageofwomenstudentswithanypreviousexperienceisveryclosetozero.Whatissurprisingisthatstudentsshowessentiallynoimprovementintheirconceptualund
