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单词 Gauss’s theorem
释义
Gauss’s theorem

Electronics and Electrical Engineering
  • The normal electric field strength, E, over a closed surface containing electric charges is given by

    E.dS=Σqε0

    where dS is a small element of area on the surface S, ε0 is the permittivity of free space, and Σq the total charge enclosed within the surface.

    If the volume enclosed by the surface contains a distributed charge density, ρe, Gauss’s theorem becomes

    E.dS=(1ε0)ρe

    where dτ is a small volume element. Since

    E.dS=divE

    then

    divE=ρeε0

    In a dielectric medium the total charge density includes an apparent charge density due to polarization of the atoms or molecules within the medium and Gauss’s theorem becomes

    divD=ρe

    where D is the electric displacement. This is one of Maxwell’s equations.

    Two main conclusions can be drawn from Gauss’s theorem. Firstly, the electric field inside a hollow conductor containing no charge is zero, the enclosed space being at the same potential as the conductor: electrical apparatus can therefore be shielded from the effect of external low-frequency electric fields by surrounding it with an earthed conductor. Secondly, any excess static charge on a conductor must reside on the outer surface.


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