An electrically isolated hollow (initially uncharged), conducting sphere has a small positively charged ball suspended by an insulating rod from its inside surface, see diagram

This causes the inner surface of the sphere to become negatively charged. When the ball is centred in the sphere the electric field outside the conducting spehere is

Options

A. zero
B. the same as if the sphere was not there
C. twice what it would be if the sphere was not there
D. equal in magnitude but opposite in direction to what it would be if the sphere was not there.

Answer

B

Explanation

b. Let the charge on the ball at center is `q`, then`-q` charge will be induced on the inner surface and `+q` on the order surface. Electric field at any point outside the sphere due to inner charges `q` and `-q` will combinely be zero. Outer charge `q` will combinely be field at outside points as it would be produced by a charge at the center. Hence presence of sphere does not affect the electric field outside the sphere.