At a distance R from a point charge q the electric field is E. If the same charge q is now placed on a copper sphere of radius R, what is the field magnitude at the surface of the sphere?

Correct answer: E

Solution

For a uniformly charged conducting sphere, the field at and outside the surface equals that of a point charge q at the centre. At the surface (r = R), E_surface = kq/R², which is exactly the field E of the point charge at distance R. So the field is unchanged, E.

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