Question

A solid uncharged conducting sphere has radius 3a contains a hollowed spherical region of radius 2a. A point charge +Q is placed at a position a distance a from the common center of the spheres. What is the magnitude of the electric field at the position r = 4a from the center of the spheres as marked in the figure by P?

(A) 0

(B) kQ/16a²

(C) 3kQ/16a²

(D) kQ/9a²

(E) None of the previous

Answer 1

The correct option is: (B) kQ/16a²

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 and the field outside the shell is as if the shell was a point charge.