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Homework Help: Potential Energy of an electron in a parallel plate capacitor

  1. Nov 12, 2012 #1
    1. The problem statement, all variables and given/known data

    What is the potential energy of an electron in a parallel plate capacitor if kept on the negative plate before being released?

    2. Relevant equations

    1/2mv^2 = qV = PE
    Capacitor Energy = 1/2QV

    3. The attempt at a solution
    1/2mv^2 = qV = PE

    However if I'm not mistaken there's also 1/2QV equation that states the energy stored in a capacitor? Which one then should I choose for this electron problem? The normal qV or the 1/2qV?
  2. jcsd
  3. Nov 12, 2012 #2


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    Homework Helper

    The force on the electron due to the E field of the capacitor is F = qE = eV/d.
    As it falls the distance between plates, the work done by this force is W = F*d = eV.
    So your have it right. The 1/2QV must for something else, perhaps the electrical energy stored in the capacitor.
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