A hollow conducting spherical shell of radius \( R \) has a total charge \( q \) distributed uniformly on its surface. The electric potential at a distance \( r \) from the centre, where \( r < R \), is:

Inside a hollow conducting spherical shell, the electric field \( E \) is zero everywhere (\( E = 0 \)) because charges reside only on the outer surface of a conductor in electrostatic equilibrium. Since the electric field is related to electric potential by \( E = -\frac{dV}{dr} \), a zero electric field implies that the electric potential remains constant throughout the interior region and is equal to the potential at the surface. Therefore, for any point where \( r < R \), the electric potential is given by \( V = \frac{1}{4\pi\varepsilon_0} \frac{q}{R} \).