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 centered in the sphere the electric field outside the conducting sphere is
Let the charge on the ball at center is q, then -q charge will be induced on the inner surface and +q on the outer surface. Field at any point outside the sphere due to inner charges q and -q will combine to be zero. Outer charge q will produce the electric 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.
6th Floor, NCC Building, Durgamma Cheruvu Road, Vittal Rao Nagar, HITEC City, Hyderabad, Telangana 500081.
