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Homework Help: Pressure on charged spherical shell, alternative solution

  1. Jun 6, 2012 #1
    1. The problem statement, all variables and given/known data
    Find the pressure on a uniformly charged spherical conducting shell of Radius R and total charge Q. The answer is (Q^2) / (32*π*ε*R^4)

    I´m fine doing this using the derivative of the energy as the sphere grows to get the force.

    My question is: Why do I get twice the answer if I think of a small surface element dA and calculate the force on it as the field E = Q/(4πεR^2) multiplied by the charge on that surface element, dQ = dA*(Q/(4πR^2) ?

    I cannot see where I double the force. How should this approach be mended?

    Thanks for reading this,

  2. jcsd
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