Two $10\ C$ charge is placed on the surface of a sphere with radius $10cm$. Find the potential at the Centre.

$1.8\times 10^{12}\mathrm{V}$

$2.8\times 10^{12}\mathrm{V}$

$1.3\times 10^{12}\mathrm{V}$

$3.8\times 10^{12}\mathrm{V}$