A conducting sphere carrying charge Q is surrounded by a spherical conducting shell.
a. What is the net charge on the inner surface of the shell?
b. Another charge q is placed outside the shell. Now, what is the net charge on the inner surface of the shell?
c. If q is moved to a position between the shell and the sphere, what is the net charge on the inner surface of the shell?
d. Are your answer valid if the sphere and shell are not concentric?

Explanation

We know that charge on facing surface is equal and
opposite.

a. Net charge on inner surface is `-Q`.
b. Net charge on the inner surface will remain `-Q`.
c. Net charge on inner surface is `-(Q+q)`.
d. Yes, as location of charge does not matter.