Question

A metal sphere is suspended from a nylon thread. Initially the metal sphere is uncharged, When a positively charged glass rod is brought close to the metal sphere, the sphere is drawn towards the rod, But if the sphere touches the rod, it suddenly flies away from the rod. Explain, why the sphere is first attracted then repelled?

Answer 1

When sphere is suspended and the charged rod is brought close, a charge opposite to the charge on the rod is induced on the part of surface of sphere near the rod. This induced opposite charge attracts the rod.
After the contact is made, due to the induced opposite charge on the surface of sphere, some amount of the charge from rod is diffused to the sphere by conduction. not both sphere and the rod have the same sign of charge. Hence they repel