Some spherical equipotential surfaces are shown in figure. The values of the potentials are 100 V, 80 V, 40 V on surfaces of radii 10 cm,12.5 cm and 25 cm. The electric field at a distance r from the common centre is
  • A
    $${{20} \over {{r^2}}}$$
  • B
    $${{10} \over {{r^3}}}$$
  • C
    $${{20} \over {{r^3}}}$$
  • D
    $${{10} \over {{r^2}}}$$

Solution