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Homework Help: Mass m oscillations with conductivity

  1. Feb 12, 2016 #1
    Sphere of mass m, and charge q is hanged on a thread of lenght l in a constant gravitational field g.
    There is infinite horizontal conductive plan which is kept at potential 0.
    Find period of small oscillations of sphere.

    So my question is next, how do i get the force due tu charge q in newtons equation.?
  2. jcsd
  3. Feb 12, 2016 #2
    If the bottom surface is a conductor, then there will be an image change of -q. You basically treat the conductor like a mirror. So now in addition to gravity you have attraction between charges.

    So the force on the sphere will roughly be:
    F = mg + kq^2/(2d)^2
    for small oscillations.
    Last edited: Feb 12, 2016
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