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Homework Help: Finding the potential difference?

  1. Mar 24, 2007 #1
    okey the question goes like this

    A plate capacitor with area A and distance d1 is charged to a potential difference of V1 between the plates. Now the distance between the plates increases to d2 = 2*d1.

    a) What is the new potential difference, V2, between the plates?

    b) Find the increase in stored energy, deltaU, an explain where this energy comes frome.

    what I have found out so far is:
    a) V2 = E*2*d1, where E = Q/(e0*A) and therefore does not change with distance.

    b) deltaU = 1/2*Q*V2 - 1/2*Q*V1

    I don't think these two answers are good enough, but I can't se what else to do, maybe use intgral?
    any help is highly appreciated:smile:

    Kind regards

  2. jcsd
  3. Mar 24, 2007 #2

    using your eqn a) what is the ratio v2/v1?
  4. Mar 24, 2007 #3
    well the ratio must be V2/V1 = d1, but this can't be the answer to a) could it?
  5. Mar 24, 2007 #4
    unless I miss my guess, it should be 2di/di=2.
  6. Mar 25, 2007 #5
    hehe yea ofcorse:smile:
    but I still don't think the ration is the answer to thequstion, thanks though:smile:
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