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Homework Help: Electrostatic potential energy of a nonconducting sphere

  1. Oct 19, 2012 #1
    1. The problem statement, all variables and given/known data
    Determine the total electrostatic potential energy of a nonconducting sphere of radius r0 carrying a total charge Q distributed uniformly throughout its volume.
    Express your answer in terms of the variables Q, r0, and appropriate constants.

    2. Relevant equations
    V = kQ/r

    U = qV

    3. The attempt at a solution
    Since the total amount of charge within the sphere is Q and the sphere has a radius of r0, we can make V = kQ/r0. Since U = qV, then U = kqQ/r0. However, I'm not sure how to express q in terms of Q.
  2. jcsd
  3. Oct 19, 2012 #2

    Andrew Mason

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    Science Advisor
    Homework Helper

    If the charge Q is uniformly distributed over the entire volume of the sphere, v, the charge density is σ = Q/v. So the charge in a volume dv is dq = σdv

    Using this charge density, work out the potential energy of a hollow sphere of inside radius r and outside radius r+dr formed around the outside of a solid charged sphere of radius r. Integrate that from r=0 to r=r0.

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