A charge Q is distributed over three concentric spherical shells of radii a, b, c ( a < b < c ) such that their surface charge densities are equal to…

A charge Q is distributed over three concentric spherical shells of radii $\displaystyle \mathrm{a}, \mathrm{b}, \mathrm{c}$ $\displaystyle (\mathrm{a}<\mathrm{b}<\mathrm{c})$ such that their surface charge densities are equal to one another. The total potential at a point at distance r from their common centre, where $\displaystyle \mathrm{r}<\mathrm{a}$, would be :