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Prove that a sphere is a conductor.

  1. Mar 5, 2015 #1
    1. The problem statement, all variables and given/known data
    How do I prove that a sphere is a conductor?

    2. Relevant equations
    E = kQ/r

    3. The attempt at a solution
    In my mind, if a sphere is a conductor, the charges formed during induction will move to the surface of the sphere as they can move freely in the conductor, and the same polarity of the charges would cause them to move as far away from each other as possible. (Hence they would be more or less evenly distributed on the surface of the sphere. However, the suggested solution was that the proof that the conductor was a conductor would be that there would be the electric field strength inside the sphere is zero. I'm not quite sure how to work that out, but would it be because there's no charge in the centre of the sphere (due to the fact that it is a conductor) that the E would be zero?

    Thank you!
  2. jcsd
  3. Mar 5, 2015 #2


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    You should post the question word for word as it was given to you.
  4. Mar 6, 2015 #3


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    Hello Roxanne, welcome to PF :smile:

    I second Sam if this is homework. If it is a more conceptual question then Gauss' theorem is a useful tool to realize that there is no (static) difference outside the sphere to distinguish between conducting and non-conducting spheres.

    Your reasoning is correct, but it doesn't help to distinguish.

    Experimentally the question is pretty difficult: you can't drill a hole without disturbing the charge situation. But the change in charge distribution due to another charge nearby might be something that can be used.

    That the problem statement as you post it is too vague is illustrated by a direct answer: "by measuring its resistance" :wink:
  5. Mar 7, 2015 #4


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    I would use induced charge.

    You can fix a strip of alufoil to the surface of the sphere, which would show if the sphere is charged or not. Initially the sphere is neutral. Put a positively charged rod near to the sphere. The charges redistribute on its surface. Free electrons of the metal accumulate near to the rod, and the opposite surface becomes positive. Touch this part with a pin, or simply with your fingertip. Remove the rod then. What happens? Why? Does the sign of the charge on the rod count? Does this experiment work with an insulating sphere?

    induced charge.JPG
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