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Homework Help: Electric Potential Energy of Three Point Charges

  1. Jul 11, 2010 #1
    1. The problem statement, all variables and given/known data

    Three equal point charges, each with charge 1.95 nanoC , are placed at the vertices of an equilateral triangle whose sides are of length 0.550m . What is the electric potential energy of the system? (Take as zero the potential energy of the three charges when they are infinitely far apart.)
    Use = 8.85×10−12 for the permittivity of free space.

    2. Relevant equations

    U = kQ1Q2/r

    3. The attempt at a solution

    So I know how to go about solving the problem. I take the potential energy between points 1 and 2, 1 and 3, and then 2 and 3 and sum them together.

    OR since it is equilateral and all the same charge and I skip a little.

    U=3KeQ2/r right?

    When I do these steps I come to a final answer of 9.56E-8 J but know that this is not right, first because Mastering Physics told me I was wrong, second because I know that it cannot approach zero unless the distance is approaching infinity. Any suggestions on where I am going wrong?
  2. jcsd
  3. Jul 11, 2010 #2
    Oh wow. Haha. Okay guys I figured it out. It wasn't nano Coulomb it was micro. Got the answer on the last try.
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