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Homework Help: Energy stored in capacitor

  1. Apr 11, 2013 #1
    1. The problem statement, all variables and given/known data

    A parallel plate capacitor with plates of area, A & separation of d is filled with LIH dielectric of relative permittivity ε. By considering energy associated with the electric field derive an expression for electric energy stored in the capacitance when a voltage of V is applied.

    2. Relevant equations
    u = 1/2 D.E
    D = εε0E for LIH material

    3. The attempt at a solution

    u = εε0E2
    E = v/d
    Energy stored is u x volume between plates
    u = εε0(v/d)2 x Ad

    u = εε0* (Av2/d)

    I should also be able to derive the same result if I consider capacitance instead of energy associated with the electric field. . . .
    . . . . but how?

    I know u = 1/2 CV2
    and C = Q/v
    so . . . . . . . . er!
    How, please
    Thank you
  2. jcsd
  3. Apr 11, 2013 #2


    User Avatar
    2017 Award

    Staff: Mentor

    (or D<->E in both equations? not sure, but it should be right that way)

    If you fix the missing factor of 1/2 in your first derivation, the result should be the same.
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