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Homework Help: Van de Graff Problem

  1. Oct 7, 2007 #1
    A van de Graaff generator puts negative charge on a metal sphere.

    Suppose the radius of the sphere is a = 6.9 cm, and the charge on the sphere is Q = -1.0×10-8 C. Determine the electric field strength at a point 1.0 cm from the surface of the sphere (outside the sphere).

    I've done this problem over and over and am not getting the correct answer.
    I've used E = F/q and made F = kq/r^2
    ...from there, I don't know what to do. Please help. Thanks
  2. jcsd
  3. Oct 8, 2007 #2


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    Science Advisor

    It's E that equals kq/r^2, and be carefl about what r means here.
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