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Homework Help: Questions about spherical conductor

  1. May 10, 2008 #1
    1. The problem statement, all variables and given/known data
    A charge Q is placed at the center of a conducting spherical shell of inner radius R1 and outer radius R2. The sphere has no net charge.

    Ok, I have some statements for this setup. Would you be kind to check them?

    3. The attempt at a solution

    1) The electric field in a distance R < R1 from the pointcharge Q is the electric field coming from the charge itself.

    2) The electric field in a distance R1 < R < R2 is zero (E-field zero inside a conductor always).

    3) In a distance R > R2 the electric field is only coming from the point charge, since the conductor has no net charge.

    4) The formula for the electric field outside a conductor: E = (sigma/epsilon_0)n. Does this only apply to the outside surface of a conductor, or also the inside surface? (In this case the inside-surface of the spherical shell)
    Last edited: May 10, 2008
  2. jcsd
  3. May 10, 2008 #2


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    If one puts a charge Q (assumed positive) in the center of a spherical 'conductor', what happens to the charges in the conductor (which if neutral, has a balance of - and + charges)?
  4. May 10, 2008 #3
    The positive charges go to the outer surface and the negative charges go to the inner surface.
  5. May 10, 2008 #4


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    What can one say about the charge densities of the inner and outer surfaces?
  6. May 10, 2008 #5
    Charge-density is the charge per area, and since the charge is the same with different sign, I guess the only thing that makes them vary is the area.
  7. May 10, 2008 #6


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    what's the definition of a conductor?
    Reilly Atkinson
  8. May 10, 2008 #7
    The electric field inside is zero?

    Am I way off with my answers in #1?
  9. May 10, 2008 #8


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    1, 2, and 3 look good to me. I'd have to think (more than I have time for at the moment!) about #4.
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