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Homework Help: Energy in a capacitor

  1. Nov 24, 2007 #1
    1. The problem statement, all variables and given/known data
    A capacitor has variable distance between the plates . It charges with a constant charge Q and the distance between the plates increase with 20%. How many percent does the energy change in the electric field between the plates?


    2. Relevant equations
    E = (1/2)QV = (1/2)CV^2 = Q^2/2C


    3. The attempt at a solution
    I remember my teacher said that the energy only depends on e. So the energy is the same.
     
  2. jcsd
  3. Nov 24, 2007 #2


    Here Q is constant.Becuase distance between the plates changes,capacitance also changes.

    [tex]C=\epsilon\frac{A}{d}[/tex]

    [tex]\epsilon[/tex] and A are also constants.
     
  4. Nov 24, 2007 #3
    ok. If I want to find the maximum energy/volume then the distance doesnt matter, right?
     
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