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Homework Help: Energy to separate charge +e and -e

  1. May 13, 2013 #1
    1. The problem statement, all variables and given/known data
    Derive an expression for the energy required to separate to infinity an electric charge +e and a charge -e, their initial separation being d.

    2. Relevant equations

    F = (q1*q2)/(4∏ * ε0 * d2)

    3. The attempt at a solution
    Basically what I've done is first make q1= +e and q2= -e and substituted them into the equation above. I then integrated this equation as show below...

    Work done = d F = d -e2 / (4∏ * ε0 * d2)

    After integrating this with respect to d, I get the answer...

    W = e2 / (4∏ * ε0 * d)

    Is this correct or did i make it all up in my head, thanks for any replies :)
  2. jcsd
  3. May 13, 2013 #2
    I think this is correct. The potential of a charge, v = kq/r , is found this way, i.e. by integrating from d to infinity of a test charge and then dividing by the charge.
  4. May 13, 2013 #3
    An easier way to do this is to work out the change in potential energy.
    W = ΔU
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