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Energy of a parallel plate capacitor homework

  1. Nov 30, 2013 #1
    Hi all

    "A parallel plate capacitor in which plates of area A are separated by a distance d, has a capacitance C = [itex]\frac{Aε_{0}ε_{r}}{d}[/itex]
    It is charged to a pd V. Neglecting edge effects, derive an equation for the electric field E in the capacitor, and show that the energy stored per unit volume is w= 0.5[itex]ε_{r}ε_{0}E^{2}[/itex]"

    I believe that the electric field in a capacitor to be equal to [itex]\frac{\sigma}{\epsilon_{0}}[/itex]
    via Gauss Law, and using V = Ed you can then get V = [itex]\frac{\sigma d}{\epsilon_{0}}[/itex].

    I have then tried to use the various equations for work done = 0.5CV^2, 0.5QV etc to no avail.

    Any help much appreciated.

    Thanks
     
  2. jcsd
  3. Dec 1, 2013 #2

    rude man

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    That would be correct if the interplate material is air, but it's not.
     
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