浙江大学大学物理甲下-chapter-29.ppt

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1、Chapter29TheElectricalPropertiesofMaterials129-1TypesofMaterials1.ConductorsConductors(includingmostmetals)arematerialsinwhichelectricchargesreadilyflow.Inconductors,eachatomgivesuponeormoreofitsvalenceelectronstotheentirematerial,whicharefreetomovewhenanexternalelectricfieldisappliedt

2、othematerial.gasofelectrons22.InsulatorsInainsulator,theelectronsareboundrathertightlytotheatomsandarenotfreetomoveundertheappliedelectricfields.Aninsulatorcancarryanydistributionofelectricchargesonitssurfaceorinitsinterior.Theelectricfieldintheinteriorofaninsulatorcanhavenonzerovalue.

3、Aninsulatorcanberegardedasacollectionofmoleculesthatarenoteasilyionized.33.SemiconductorsInasemiconductor,perhapsoneatomin1010to1012mightcontributeanelectrontotheflowofelectricity(electriccurrent)inthematerial.UnderstandingthebehaviorsofsemiconductorsrequirestheknowledgeofQuantumMechan

4、ics.Semiconductorshaveplayedanimportantroleinmodernelectronictechnology.Commonlyusedsemiconductorsincludesilicon,germaniumandlotsofcompounds.44.SuperconductorsUndercertainconditions,ofteninvolvingcoolingtoverylowtemperatures,electricchargecanflowthroughsomematerialwithnoresistanceatall

5、.Thematerialsundertheseconditionsarecalledsuperconductors.UnderstandingsuperconductivitydoesalsoneedQuantumMechanics.529-2AConductorinanElectricField(StaticConditions)Thecontentinthissectionisonlyareview.SupposeweplacearectangularslabofaconductorinauniformelectricfieldE0,61.Theelectric

6、fieldiszeroatanypointinsideaconductorinelectrostaticequilibrium.Theconductorbecomesanequipotential,anditssurfacesbecomeequipotentialsurfaces.2.Whenaconductorisinelectrostaticequilibrium,onlypointsonitssurfacecanhavenetcharge.3.Theelectricfieldatthesurfaceoftheconductorisperpendicularto

7、thesurface.4.Theexcesschargeonaconductorinelectrostaticequilibriumismoreconcentratedatregionsofgreatercurvature.Thepropertiesofconductorinelectrostaticequilibrium7Ingeneral829-3AConductorinanElectricField:(DynamicConditions)1.ElectricCurrentIndynamicsituation,thereisnoaccumulationofe