Charge  $Q$ coulombs is uniformly distributed throughout the volume of a solid hemisphere of radius  $R$ metres. Then the potential at centre  $O$ of the hemisphere in volts is $\frac{1}{4\pi {\epsilon }_0}\frac{3Q}{nR}$. The value of n is 

 

Lets consider a solid sphere with a charge 2Q which is uniformly distributed across the volume.

The electric potential at the centre will be $\frac{1}{4\pi {\epsilon }_0}.\frac{3}{2}\frac{2Q}{R}$

The potential due to each hemisphere will be $\frac{1}{4\pi {\epsilon }_0}.\frac{3}{2}\frac{2Q}{R}\times \frac{1}{2}=\frac{1}{4\pi {\epsilon }_0}.\frac{3}{2}\frac{Q}{R}$

So, Potential at the centre of the hemisphere is $V_0$= $\frac{3}{2}\times \frac{1}{4\pi {\epsilon }_0}\frac{Q}{R}$