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Homework Help: Electric Potential of charged isolated body.

  1. Jul 1, 2016 #1
    1. The problem statement, all variables and given/known data
    Two equal isolated metallic bodies A & B start with no charge and zero potential. A is given a charge giving B the potential U. B is then Grounded giving A the potential U.

    What potential did A have before B was grounded?

    Hint: Use symmetry and use potential coefficients.

    2. Relevant equations
    V=1/(4*pi*eps) * int(e_density/R dl)

    3. The attempt at a solution
    Don't know where to start here. The answer includes only U as variable. I think it's a question about relations.
    Last edited: Jul 1, 2016
  2. jcsd
  3. Jul 1, 2016 #2


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    Suppose A started with charge Q, and this led to potential V at A and U at B.
    If A had started with charge 2Q instead, what would the two potentials have been?
  4. Jul 1, 2016 #3
    2V and 2U.

    I should have stated that with no charge both potentials is zero.

    I don't see your point. The anser is V_A = U (√ 5 +1)/2
  5. Jul 1, 2016 #4


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    It's the first small step. Generalise it as a relationship between the charge placed on one of the objects and the consequent changes to the potentials of each object.
    (Encouragingly, the answer you quote is the one I got.)
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