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Homework Help: Charges at the corners of a square.

  1. Sep 26, 2012 #1
    1. The problem statement, all variables and given/known data
    Four positive charges are located on the corners of a square of side-length a.
    The charges are A=4, B=2, C=8

    Determine the magnitude and direction of the electric field experienced by charge q in terms of q, a, and ke.

    2. Relevant equations
    Ex = [q1*q2/(4*∏*εo*a^2)]cosθ
    Ey = [q1*q2/(4*∏*εo*a^2)]sinθ

    3. The attempt at a solution

    Ex = 4keq2/a^2 + 2keq2/[(2a2)^.5]cos45
    Ey = [2keq2/(a*21/2)]sin45 + 8keq2/a2

    I know I have to sum up the x components from A->q and B->q for the x component of the vector, and then sum up the y components from B ->q and C->q for the y component and then use the pythagorean theorum to find the magnitude. For the direction I have to take the tangent of the y-component/x-component. I am just confused because there aren't any values given. Would the above be correct?
  2. jcsd
  3. Sep 26, 2012 #2


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    Check the expressions for the denominators.
  4. Sep 26, 2012 #3
    I just went on fearofphysics.com (lifesaver) and have realized my error. I had the distance squared for one fraction, but not the other one. Thank you very much.

    Edit: It WOULD be one of those errors.
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