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Homework Help: Capacitance if inner sphere is earthed

  1. May 9, 2012 #1
    1. The problem statement, all variables and given/known data
    Two spherical concentric conductors of radius a and b (b>a). Larger conductor has charge Q and the inner conductor is earthed. Find capacitance

    2. Relevant equations

    3. The attempt at a solution
    Well i have spent a lot of time on this but couldnt get the desired answer which is
    4πε b^2 / (b-a)

    Okay i know the inner sphere should be at zero potential, so some negative will get induced on the inner sphere which is equal to aQ/b.
    Well after this capacitance = q/V(q = aQ/b) and i get the answer 4πεa which is wrong
    I need help
  2. jcsd
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