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Homework Help: Electric Potential-finding unknown distance

  1. Feb 16, 2010 #1
    1. The problem statement, all variables and given/known data

    A 1.5 10-9 C charge is at the origin, and a -1.50 10-9 C charge is 4.5 m to the right on the positive x-axis. The electric potential is -1.8 V at a point on the x-axis that is a distance d to the right of the negative charge. Find d.

    2. Relevant equations

    V = k [sum] (q/r)

    3. The attempt at a solution

    -1.8V = k [(1.5 x 10-9 / 4.5 + x ) + (-1.5 x 10-9 / x )]

    Maybe I'm doing the algebra incorrectly, but I continue to get the wrong answer although I think the set-up is correct.
  2. jcsd
  3. Feb 16, 2010 #2


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    Homework Helper

    The equation is incorrect, it should be

    -1.8V = k [1.5 x 10-9 / (4.5 + x ) + (-1.5 x 10-9 / x )]

    Show how do you get x.

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