A charge of total amount $Q$ is distributed over two concentric hollow spheres of radii $r$ and $R ( R > r )$ such that the surface charge densities on the two spheres are equal. The electric potential at the common centre is (1) $\frac { 1 } { 4 \pi \varepsilon _ { 0 } } \frac { ( R - r ) Q } { \left( R ^ { 2 } + r ^ { 2 } \right) }$ (2) $\frac { 1 } { 4 \pi \varepsilon _ { 0 } } \frac { ( R + r ) Q } { 2 \left( R ^ { 2 } + r ^ { 2 } \right) }$ (3) $\frac { 1 } { 4 \pi \varepsilon _ { 0 } } \frac { ( R + r ) Q } { \left( R ^ { 2 } + r ^ { 2 } \right) }$ (4) $\frac { 1 } { 4 \pi \varepsilon _ { 0 } } \frac { ( R - r ) Q } { 2 \left( R ^ { 2 } + r ^ { 2 } \right) }$
A charge of total amount $Q$ is distributed over two concentric hollow spheres of radii $r$ and $R ( R > r )$ such that the surface charge densities on the two spheres are equal. The electric potential at the common centre is\\
(1) $\frac { 1 } { 4 \pi \varepsilon _ { 0 } } \frac { ( R - r ) Q } { \left( R ^ { 2 } + r ^ { 2 } \right) }$\\
(2) $\frac { 1 } { 4 \pi \varepsilon _ { 0 } } \frac { ( R + r ) Q } { 2 \left( R ^ { 2 } + r ^ { 2 } \right) }$\\
(3) $\frac { 1 } { 4 \pi \varepsilon _ { 0 } } \frac { ( R + r ) Q } { \left( R ^ { 2 } + r ^ { 2 } \right) }$\\
(4) $\frac { 1 } { 4 \pi \varepsilon _ { 0 } } \frac { ( R - r ) Q } { 2 \left( R ^ { 2 } + r ^ { 2 } \right) }$