A spherical shell of radius R is given charge 3q on its surface and a point charge q is placed at distance R/2 from its centre C. Also there is a charge 2q placed outside the shell at a distance of 2R as shown. Then:

The electric potential at the centre C due to charges on the outer surface of shell is $-\frac{Kq}{R}$ after closing the switch S.

Charge flown through the switch into earth after closing the switch S is 4q.

The magnitude of electric field at the centre C due to charges on the surface of shell is $\frac{Kq}{R^2}$ before closing the switch S.

The electric potential at the centre C due to charges on the outer surface of shell is $-\frac{Kq}{R}$ before closing the switch S.