Gauss law.ppt

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1、Chapter23Gauss’Law11、ElectricfieldlineElectricfieldlineandFlux（电场线和电通量）Magnitude:thenumberoflinesperunitareaisproportionaltothemagnitudeofDirection:thedirectionofthetangenttoafieldlineatapointgivesthedirectionofFaraday“forceline”23电偶极子4一对等量正点电荷5一对异号不等量点电荷6平板电容器7Charactersofelectricfie

2、ldlines:Electricfieldlinesoriginatefrompositivechargeandterminateatnegativecharge.电场线从正电荷发出到负电荷终止，中间不会间断。不会闭合，不会交叉。ThesecharacterscanbedescribedbyGauss’sLaw.8ElectricFlux(电通量)：nESSurfacevector（面矢量）1、ElectricFluxforthesurface△Sand△S’Then通过某曲面电场线的条数Thenumberofelectricfieldlinescrossa

3、certainsurface92、theelectricfluxforanarbitraryGaussiansurface3、theelectricfluxforaclosedGaussiansurfaceThedirectionofsurfacevectorextendsfrominwardtooutward10（1）thefluxofelectricfiledduetoapointchargethroughasphericalsurfaceGauss’LawGauss’lawrelatesthenetfluxofanelectricfieldtothenetc

4、hargethatisenclosedbythesurface.11设外有一封闭曲面，两曲面之间没有电荷，由电场线的连续性可知即同一点电荷激发的场强的电通量与封闭曲面的形状无关，只与点电荷电量有关。（2）thefluxofelectricfiledduetoapointchargethroughanarbitraryclosedsurface12（3）thefluxofelectricfiledduetoanychargedsystemthroughanarbitraryclosedsurface13AchargedisolatedConductorElectro

5、staticequilibrium(静电平衡)Conductorhasmanyfreeelectrons.Whenaconductorischargedorplacedinaelectricfieldtheconductionelectronswillquicklydistributethemselvesinsuchawaythatthenetinternalelectricfieldiszero,andthereisnomovementofcharge.当导体带电或至于外静电场中，导体内电荷很快移动使导体内部电场为零，且导体上无电荷移动。141、Aconduct

6、orisplacedinanexternalstaticelectricfield内部电场为零表面电场垂直于表面152、achargedisolatedconductor16Aconductorwithacavity（中空的导体）Thereisnonetchargeonthecavitywalls;allthechargeremainsontheoutersurfaceofconductor.17ApplyingGauss’Lawtoobtaintheelectricfieldduetochargedsystem适用范围：高斯定理适用于求解具有空间对称性的电荷体系

7、的电场关键：分析对称性选取合适的高斯面，把积分化成乘积对称性原理（皮埃尔∙居里1894）：对称的原因→对称的结果18ApplyingGauss’sLaw1:CylindricalSymmetry（轴对称或旋转对称）Findtheelectricfielddistributionduetoauniformlychargedlongcylindricalrod.（均匀带电长杆）19ApplyingGauss’sLaw2:PlanarSymmetry（平移对称）s+SSSsEEFindtheelectricfielddistributionduetoauniformly

8、charg