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Confusion: Van de Graaff generator

  1. Dec 3, 2011 #1
    My physics book explains a van de Graaff in this way:

    A small conducting sphere of radius a and carrying charge q is located inside a larger shell of radius b that carries charge Q. A conducting path is momentarily established between the two conductors, and the charge q then moves entirely to the outer conductor, because the charge on a conductor always moves to its outer surface.

    But in any actual machine, you'd have to punch a hole in the outer sphere to bring the charge inside; wouldn't that merge the inner and outer surfaces? You can't even apply Gauss' Law like usual because the Gaussian surface would have to pass through the hole, and there'd be a nonzero field there.

    Am I just completely misunderstanding it?

    Edit: In addition, since the potential of the outer shell is so big (and should be uniform throughout), why doesn't charge flow off it onto the belt?
    Last edited: Dec 3, 2011
  2. jcsd
  3. Dec 3, 2011 #2


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    The hole is small enough that its influence is negligible.
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