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15.3Gauss’lawMassfluxthroughareaAForaclosedsurfacewithoutwardnormal
SimilarlywecandefinethefluxofafieldEGauss’lawreadsor
Forapointcharge,duetosymmetry,asphericalGaussiansurfacecenteredonthechargeisappropriate.theelectricfieldandforceonatestchargeq0:UsingGauss’lawCoulomb’sLaw
whereisthesolidanglespannedbydSovertheoriginofvectorr–r,Coulomb’sLaw
4p0ForoutwardnormaldqdSrr
Guass’LawGauss’lawistrueforanyE(t)So,Gauss’lawandCoulomb’slawareequivalentinthestaticcase.
Charge?field?motion?equilibrium?Ein=0,E//=0F=0?qin=0Inaninsulatedconductor:Guass’Law
TestGauss’lawCoulomb’slaw
Fieldofaninfinitelineofchargeoflineardensityl.Example15.5Gaussiansurface
Fieldofaninfinitesheetofchargeofarealdensitys.AGaussiansurfaceExample15.6
Fieldofinfinitesheetofchargewiththicknessd.GaussiansurfaceExample15.7
Insemiconductorp-njunction,Forr(x)=–eax?(thicknessxm)howtouseGauss’law?
ElectricfieldnearconductorsurfaceofarealdensitysExample15.814
TypicallytheearthhasasmallE=130N/CdownwardExample15.9
Dielectricstrengthistheminimumfieldstrengthtobreakdownmaterial.WhenR=10–2m,Q=3.3×10–8C.WhileR=1m,Q=3.3×10–4CExample15.10Fordryair,itisForQonasphere,conditionofnotbreakdownis
AtomicmodelsThomsonmodel(plumpuddingmodel)Rutherfordnuclearatommodel1?
AtomicmodelsRutherfordscattering:backscattering“fireda15-inchshellatapieceoftissuepaperanditcamebackandhityou”
Example15.11InduceddipoleofanatominE0InduceddipoleisExample15.11(Sq=0)
15.4Electricpotential
dipoleproblemOddoverra
Forcontinuousdistributionofcharges
Potentialnearinfinitesheetofcharge.Takingt
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