Potential at a point due to a system of charges is the sum of potentials due to individual charges
Consider a system of charges q1, q2, q3, …qn with positive vectors r1, r2, r3,…..rn relative to the origin P.
The potential V1 at P due to charge 'q1' is given by 
Similarly, the potential at P due to charge 'q2' is 
We know the potential at 'P' is the due to total charge configuration and is the algebraic sum of potentials due to individual charges (By superposition principle).
V = V1 + V2 + v3 + ….. + Vn
From our previous chapter, we learnt that for a uniformly charged spherical shell, the electric field outside the shell is as if the entire charges are concentrated at the centre. Thus, the potential outside the shell is given by
where 'q' is the total charge on the shell and 'R' the radius. Electric field inside the shell is zero which implies potential is constant inside and equal to its value at the surface, which is learnt in the next topic.
