A hollow metal sphere of radius 5 cms is charged such that the potential on its surface is 10 volts. The potential at the centre of the sphere is

1) zero

2) 10 volts

3) same as at a point 5 cms away from the surface

4) same as at a point 25 cms away from the surface  

A hollow metal sphere of radius 5 cm is charged such that the potential on its surface to 10 V. The potential at the centre of the sphere is

The electric potential at the surface of a uniformly charged sphere is 475 V. At a point outside the sphere at a (radial) distance of 19.0 cm from its surface, the electric potential is 100 V. (The potential is zero very far from the sphere.) What is the radius of the sphere, and what is the charge of the sphere?