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Homework Help: Potential difference?

  1. Sep 13, 2011 #1
    1. The problem statement, all variables and given/known data

    Assume we have cavity in conductor. In the cavity we have +3q charge and conductor charge is distributed uniformly and is +7q.
    With Gaus law we now that E=0 inside the conductor becaus Q enclosed is 0. But I have been wondering is there potential difference from inner wall to outer wall of conductor?
    There is -3q in the inner wall and +4 outer wall and inside conductor E=0 so V= constant but is there potential leap between inner and outer wall?

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Sep 13, 2011 #2


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    What makes you say that there is a potential difference?
  4. Sep 13, 2011 #3


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    I can't help with this, but I am trying to picture it. The charge distribution on the outside of a block of aluminium I can visualize. And I can picture a hole being drilled into the block. But how are you going to keep those 3q charges inside the hole? It's a conductor, so they will succeed in migrating to the outside and distributing themselves apart from the others.

    These are static charges? Then I think there can be no potential difference between any two points on the conductor; the charges are free to move to reposition themselves so that all points on the surface of the conductor are at a uniform potential.
  5. Sep 13, 2011 #4


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    It is not only the actual charge that is important, but the charge density on each surface. The outer surface is naturally larger and thus will require a greater total charge in order to have the same charge density as the inner surface, thus maintaining a zero field inside the conductor.
  6. Sep 13, 2011 #5
    well asume the conductor is spherical, and theres sphrical cavity in it. charge +3q in its origo, inner wall of conductor is 0-->a and outer wall is 0-->b.

    well if u draw Gaussian surface around the charge in the cavity then E is not zero, r<a, then there`d be potential difference inside the cavity, but if u draw GS a<r<b theres not. So I am thinking that just before the inner surface theres different potential than outside the conductor due to different charge of the surface...I know I explained it very hard way...Can I post here a picture?

    E: Yes I can!
    Last edited: Sep 13, 2011
  7. Sep 13, 2011 #6
    here`s the picture!!!! as you can see I am next Da Vince :D

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