Question

An uncharged spherical conducting shell surrounds a charge -q at the center of the shell. When electrostatic equilibrium is reached, the charges on the inner and outer surfaces of the shell are respectively

A. +q, -q

B. -q, +q

C. +q, -2q

D. +2q, -q

E. +q, 0

The answer for the question should be A, but I do not know how to get to that answer.

Answer 1

To balance the charges, the inner charge at the center will always induce a charge on the inner surface of the shell. This charge will be equatl to the inverse of charge. It means if there is +q charge at the center, then charge induced on inner shell will be -q and if there is -q charge at the center, then charge induced will be +q. However, to balance this inner charge, an equal and opposite charge must be present on the outer surface.

Therefore, the correct option is option (A)