Question

A rod made from insulating material carries a net charge, while a copper sphere is neutral. The rod and the sphere do not touch. Is it possible for the rod and the sphere to (a) attract one another and (b) repel one another? Explain.

Answer 1

As the charged insulating rod approaches the sphere (not in contact), free electrons in the sphere move. If the rod is negatively charged, free electrons move to the side of the sphere opposite the side with the rod. If the rod is positively charged, the free electron moves to the side of the sphere with the rod. In either case, the region of the sphere near the rod acquires a charge with the sign opposite to that on the rod.

a. Since opposedly charged objects always attract each other, the rod and ball always experience mutual attractive forces.

b. Since the side of the sphere near the bar always has the opposite charge to the charge of the rod, the rod and the sphere always attract each other. They do not repel each other.