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Electrodynamics problem: charge origin?

  1. Feb 27, 2008 #1
    [SOLVED] Electrodynamics problem: charge origin?

    When you have an insulating region within a conductor and an electric field is applied such that a current flows, this current will be made to move around the insulating region.

    -I assume a charge distribution will arise on the surface of the insulator to make this possible

    with an electric field to the right, to divert the currents flowing to the right one needs a positive charge at the left of the insulator to divert these currents around it; the situation is then:

    E---> + I - (with + &- the surface charges and I the insulator)

    But this is opposite of what one would expect from bound charges in an electric field. Here one would expect the postive charge to displace along the direction of the electric field so that -I+ will occur. What is happening here phsyically? Are the charges not the bound charges of the insulator but actually a pileup of free charges making up the currents in the conductor? Why then don't they just go around the insulator? Or is my view that charges are responsible for diverting the currents around the insulator incorrect?

    -I also assume that in order to have no currents flowing into the insulator the component of the current normal to the sphere vanishes just outside it, which will mean the normal component of the electric field has to vanish there as well.

    I'm figuring this will have to be the case and surface charges being responsible for the cancellation of the (normal component of the) electric field. But what then is the origin of these charges as they do not seem to be bound charges of the insulator?
  2. jcsd
  3. Feb 27, 2008 #2
    I'm sorry, I saw problems where there were none. I get it now.
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