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Question:
Why do the free electrons in a conductor all reside on the surface? To maximize distance between them (or minimize total energy), should not some be in the middle?



Replies:
Conductors maintain neutrality within themselves. If, for example, you were to take a neutral conductor and put some extra charge in the the middle somewhere. Now this charge will establish a field which will cause electrons in the conductor to move ( positive ions being fixed with the lattice), and electrons adjust their positions so that the field vanishes inside the conductor - otherwise electrons will have to keep moving inside, and it can be shown that this is not possible. This readjustment of electrons leads to charge neutrality inside the conductor, so the excess charge appears only on the surface. Such a thing does not happen inside nonconductors as electrons can not move freely inside the material.

Jasjeet



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