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Homework Help: Calculating charge outside capacitor plates

  1. Jun 5, 2010 #1
    1. The problem statement, all variables and given/known data
    A capacitor made of two parallel uniformly charged circular metal disks carries a charge +Q and -Q on the inner surfaces of the the plates and very small amounts of charge +q and -q on the outer surfaces of the plates. Each plate has a radius R and thickness t, and the gap distance between the plates is s. How much charge q is on the outside surface of the positive disk, in terms of Q?

    3. The attempt at a solution
    I was going to try and find the electric field at the fringe of the plate by summing up all the contributions of the charges, by treating the faces of the plates as different charged plates.

    Fringe field = E+Q + E-Q + E(-fringe) + E(+fringe)
    Fringe field - E+Q - E-Q = E(-fringe) + E(+fringe)

    I know that magnitude of +q and -q are the same so I would rearrange to find q.

    Have I made correct assumptions???
  2. jcsd
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