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Homework Help: Why is the electric field inside a conductor zero?

  1. Jan 31, 2012 #1
    1. The problem statement, all variables and given/known data
    Why is the electric field, in static equilibrium, equal to zero.

    3. The attempt at a solution

    The only way I can see why is to picture that there was an electric field inside a conductor. The field would cause the electrons to move freely inside the conductor. This movement of electrons would cancel out the electric field.

    That's my two cents. I'm sure I could expand on this more, but I'm confused because I'm having a really hard time trying to picture this in my head.
     
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  3. Jan 31, 2012 #2

    HallsofIvy

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    You can also show this the same way you show that the gravitational force inside a sphere is 0. Given a point, P, inside the sphere, take a small section of surface area on the surface of the sphere and draw a line from every point in that section through P to the other side of the sphere. Note that the area will be directly proportional to the square of the distance from P and since the force is inversely proportional to the square of the distance, the force from the two sections cancel.
     
  4. Jan 31, 2012 #3

    SammyS

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    Yes, that's the basic idea.

    In a conductor charge is (relatively) free to move. If there were an electric field within a conductor, charges would move. They would move in such a way and to such locations so as to cancel that field.

    As a result, any excess local charge can only reside on the surface of a conductor under conditions of equilibrium.
     
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