Question

A solid, uncharged conducting sphere of radius 3a contains a hollowed spherical region of radius a. A point charge +Q is placed at the common center of the spheres. Taking V = 0 as r approaches infinity, the potential at position r = 2 a from the center of the spheres is:

(A) 0

(B) 2kQ/3a

(C) kQ/3a

(D) kQ/a

(E) kQ/2a

Answer 1

The correct option is: (C) kQ/3a

Explanation:

Since the spherical shell is conducting, a charge of –Q is induced on the inner surface. This gives a charge of +Q on the outer surface since the spherical shell is neutral. As E = 0 inside the conducting shell, the potential inside is constant and the same as on the surface, which is kQ/r