A charge of 6 µC is given to a hollow metallic sphere of radius 0.2 m. Find the potential at (1) the surface and (ii) the centre of the sphere.
Given charge: $Q = 6\,\mu\text{C} = 6\times10^{-6}\,\text{C}$
Radius: $R = 0.2\,\text{m}$
Potential on the surface of a sphere:
$V = \dfrac{1}{4\pi\varepsilon_0}\dfrac{Q}{R}$
Using $\dfrac{1}{4\pi\varepsilon_0} = 9\times10^9$,
$V = 9\times10^9 \cdot \dfrac{6\times10^{-6}}{0.2}$
$V = 9\times10^9 \cdot 30\times10^{-6}$
$V = 270\times10^{3}$
$\boxed{V_{\text{surface}} = 2.7\times10^5\ \text{V}}$
For a hollow metallic sphere:
$V_{\text{centre}} = V_{\text{surface}}$
$\boxed{V_{\text{centre}} = 2.7\times10^5\ \text{V}}$