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A copper sphere carries a surface charge density sigma. What is the magnitude of the electric field just outside its surface?

1. sigma/epsilon0
2. sigma/2epsilon0
3. sigma
4. sigma/2

Correct answer: sigma/epsilon0

Solution

For any charged conductor, applying Gauss's law to a pillbox at the surface gives the external field as sigma/epsilon0, directed normal to the surface. The field inside the conductor is zero.

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