Question

A spherical conducting shell of inner radius r1 and outer radius r2 has a charge q is placed at the center of the shell.what is the surface charge density inside and outside the shell

Answer 1

outer surface will have the same amount of charge present as that placed inside the sphere.. since +q is placed inside the hollow sphere equal amount of charge ( Negative) will develop on it's surface.. this should be enough for you to find out the Surface charge density on both the inner and outer surfaces