Question

You are given two metal spheres mounted on portable insulating supports. Find the way to give them equal and opposite charges. You may use a glass rod rubbed with silk but may not touch it to spheres. Do the spheres have to be of equal size for your method to work?

Answer 1

By keeping the two spheres in contact and bringing a charged rod near one of the spheres, equal and opposite charges will be induced on two spheres as shown in Fig.

By keeping the rod in position, remove the sphere on the RHS by insulating stand to some distance apart Fig. (b).

Next, remove the glass rod. Now the two spheres will carry equal and opposite charge. The charge on the two spheres will be equal irrespective of their sizes.