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Question regarding Gauss's Law

  1. Jul 5, 2007 #1
    I had a question regarding how Gauss's law works. I have attached an image that depicts two scenarios.

    Basically, if you assume the blue lines are a conductor and the green and red dots both contain an equal amount of charge, what is the expected behavior of the red dot?

    As I understand it, in the lower scenario, Gauss's law allows the blue conductor to shield the red dot from the green dot; thus, nothing happens to the red dot. What happens in the second scenario? (The one I drew above) Does the red dot remain where it is or move away -- and please explain why..

    - Wired Guy.

    Attached Files:

  2. jcsd
  3. Jul 6, 2007 #2


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    What happens is that, the charge distributes in such a way so that the electric field due to the induced charges on the inner surface of the conductor cancels exactly with the field due to the charge inside the cavity, at all points in the conductor.

    So, the two charges inside the cavity won't expereince the field of each other and won't move.
  4. Jul 7, 2007 #3
    So in the second case the green dot moves while the red dot remains in the same place?

    I was curious if the charges that move to cancel out the effects of the green charge were on the external or internal surface of the cage. Could you also refer me to a place where I can read more about this phenomena?

    Thanks in advanced,
    - Wired Guy
  5. Jul 9, 2007 #4
    Are there parts of my question that are unclear? or is this the wrong forum to be asking the question on? (Generally I find the feedback to be much more active on this board).
  6. Jul 9, 2007 #5

    Doc Al

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    In the lower scenario the field from the green dot affects the charge distribution on the outer surface of the conductor, but the conductor itself shields the red dot from being affected by the field of the green dot.

    In the upper scenario both dots are shielded from each other. Neither dot is affected by the presence of the other.
  7. Jul 10, 2007 #6


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    The feedback is usually more active. I'm sorry I couldn't reply and left this hanging. I was traveling.

    Thanks for stepping in Doc Al :smile:
    Last edited: Jul 10, 2007
  8. Jul 10, 2007 #7
    Thanks for the help guys!
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