Q.
Figure shows a annular disc of outer radius $R$ inner radius $R,$ and uniform surface charge density. Total charge is $q.$ The potential at the centre is $\frac{k q}{r^{'}}\left(k = \frac{1}{4 \pi \left(\epsilon \right)_{0}}\right)$ where $r^{'}$ is

NTA AbhyasNTA Abhyas 2020
Solution: