An uncharged metal sphere, A, is on an insulating base. A second sphere, B, of the same size, shape, and material carrying charge Q is brought close to, but not touching, sphere A. Describe what happens to the charges on A and B as they are brought close but not touching. If we now remove sphere B and place it far away, what is the charge on sphere A

0

Explanation:

If we bring the charged sphere B close to, but not touching it , to the uncharged sphere A, as charges can move freely on the conductor, a charge -Q will be built on the outer surface of the sphere A, facing to sphere B.As the sphere A must remain neutral, a charge Q will be built on the surface, on the side farther to the sphere B, as the following condition must be met:

       Q +(-Q) =0.

If we now remove sphere B, and place it far away, there will be a charge redistribution within sphere A, making to disappear the separation between Q and -Q.The total charge on sphere A must be 0, as there is no charge transfer from sphere B to sphere A.