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E, D and P inside a material

  1. Sep 9, 2014 #1
    A problem involving E, D & P. I have the answer but not sure why for the P bit.A bit of clarification if someone could, please.

    A thick sheet of polystyrene, of relative permittivity ε = 2.5, is placed
    normal to a uniform electric field of magnitude 500Vm−1 in air.

    Find the magnitudes of the electric field E, the electric displacement D and the polarization P inside the material.

    OK div D = ρf
    and D = εε0E
    Boundary conditions Doutside = Dinside → εoutEout = εε0Ein

    Ein = Eout / ε
    Ein = 500/2.5
    Ein = 200 Vm-1

    Dout = Din = ε0 Eout
    Dout = 8.85x10-12 x 200
    Dout = 1.77x10-9

    Fine so far . . .

    When I get down to calculating P I have to use

    Din = ε0Ein + Pin

    why, when everything else has the suffix "in" do I use ε0? Shouldn't it be just plain ε?

    Thanks in advance.
  2. jcsd
  3. Sep 12, 2014 #2
    I'm sorry you are not finding help at the moment. Is there any additional information you can share with us?
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