An electrically isolated hollow (initially uncharged) conducting sphere has a small positively charged ball suspended by an insulating rod from its inside surface (see figure). 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. Electric field at anypoint outside the sphere due to inner charges q and −q will combinely 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.