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Homework Help: Gauss's Law and charged conductors

  1. Oct 4, 2011 #1
    A conductor carries a net charge +Q. There is a hollow cavity inside the conductor that contains a point charge -Q. In electrostatic equilibrium,what is the charge on the outer surface of the conductor?

    A. -2Q
    B. -Q
    C. 0
    D. Q
    E. 2Q

    I know that the answer is 0, however, I cannot understand why. i would think that the inner surface of the conductor is +Q to offset the -Q point charge inside, which would make the outer surface +Q in order to account for the net +Q charge. However, that is not the case.

    Can some one please offer me some help understanding this problem?Thanks so much
  2. jcsd
  3. Oct 4, 2011 #2


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    If the charge on the inner surface of the conductor is +Q, and the net charge on the conductor is also +Q, how much charge is left over to distribute on the outer surface?
  4. Oct 4, 2011 #3
    Oh ok, I see. It's 0. For some reason i thought that the +Q and the -Q would cancel out.
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