A thin spherical conducting shell of radius R has a charge q. Another charge Q is placed at the centre of the shell. The electrostatic potential at a point p a distance $\frac{\mathrm{R}}{2}$ from the centre of the shell is

• A

  $\frac{(\mathrm{q}+\mathrm{Q})2}{4{\mathrm{\pi \epsilon }}_0\mathrm{R}}$

• B

  $\frac{2\mathrm{Q}}{4{\mathrm{\pi \epsilon }}_0\mathrm{R}}$

• C

  $\frac{2\mathrm{Q}}{4{\mathrm{\pi \epsilon }}_0\mathrm{R}}-\frac{2\mathrm{q}}{4{\mathrm{\pi \epsilon }}_0\mathrm{R}}$

• D

  $\frac{2\mathrm{Q}}{4{\mathrm{\pi \epsilon }}_0\mathrm{R}}+\frac{\mathrm{q}}{4{\mathrm{\pi \epsilon }}_0\mathrm{R}}$