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Homework Help: Charged ring with oscillating particle

  1. Sep 12, 2012 #1
    1. The problem statement, all variables and given/known data
    A ring of radius 6 cm that lies in the yz
    plane carries positive charge of 7 μC uniformly
    distributed over its length. A particle of mass
    m carrying a charge of −7 μC executes small
    oscillations about the center of the ring on its
    axis with an angular frequency of 15 rad/s.
    Find the angular frequency of oscillation of
    the mass if the radius of the ring is doubled
    while keeping the linear charge density on the
    ring constant.

    2. Relevant equations
    F = kQq/r2

    3. The attempt at a solution

    I don't even know where to start with this one. To be honest, I'm not entirely sure what's actually going on. Is the particle going around the ring? Is it going right through it? I have no idea.
  2. jcsd
  3. Sep 12, 2012 #2


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    Homework Helper

    Due to the simitry, the field at the centre of the ring is zero. Search for an expression for a field along the axis of a charged ring in the web. Since distance x is very small, neglect the higher power of x in the expression. Now F = E( - q) = ma. And since in SHM, a = -ω2x, you can compare the two angular velocities.
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