Discuss the method of charging of two spheres by without contact method.

Explanation

(i) Bring two metal spheres, A and B, supported on insulating stands, in contact as shown in figure (a).
(ii) Bring a positively charged rod near one of the spheres, say A, taking care that it does not touch the sphere.

The free electrons in the spheres are attracted towards the rod. This leaves an excess of positive charge on the rear surface of sphere B. Both kinds of charges are bound in the metal spheres and cannot escape. They, therefore, reside on the surfaces, as shown in figure (b).
The left surface of sphere A, has an excess of negative charge and the right surface of sphere B, has an excess of positive charge.
As the negative charge starts building up at the left surface of A, other electrons are repelled by these. In a short time, equilibrium is reached under the action of force of attraction of the rod and the force of repulsion due to the accumulated charges. Figure (b) shows the equilibrium situation.
The accumulated charges remain on the surface, as shown, till the glass rod is held near the sphere. If the rod is removed, the charges are not acted by any outside force and they redistribute to their original neutral state.
(iii) Separate the spheres by a small distance while the glass rod is still held near sphere A, as shown in figure (c). The two spheres are found to be oppositely charged and attract each other.
(iv) Remove the rod. The charges on spheres rearrange themselves as shown in figure (d). Now, separate the spheres quite apart.
The charges on them get uniformly distributed over them, as shown in figure (e).
(v) In this process, the metal spheres will each be equal and oppositely charged. This is charging by induction.