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HELP! Potential energy of proton in capacitor

  1. Feb 8, 2010 #1
    1. The problem statement, all variables and given/known data

    I have attached the image. The question is --

    What is the potential energy of a proton at the midpoint of the capacitor?

    I know this is an extremely easy problem, but I can't seem to get the formula right...

    2. Relevant equations

    I tried U = qV, using 1.6*10^-19 * 150V (because it is in the middle). What am I doing wrong? Is this not the right formula?

    3. The attempt at a solution

    Attached Files:

  2. jcsd
  3. Feb 8, 2010 #2


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    Gold Member

    Hi and welcome to PF!
    I know a hard way to solve the question. I'm not sure it is of help in your case, but in case you've taken calculus 3 then it's ok.
    [tex]\phi (r)= \int _{\infty}^r \vec E \cdot d \vec l[/tex]. Thus the almost only difficulty would be to calculate the E field between the plates of the capacitor.

    There might be of course a much faster way to solve it. So if anyone can help, welcome!
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