1. The problem statement, all variables and given/known data A spherical shell with inner radius A and outer radius 3A which has a uniform charge density, i.e charge per unit volume, p0. Find difference in electric potential between the center of the shell and a point a distance 2A from the center. 2. Relevant equations The answer given is. -(p0A2)/3ε0 3. The attempt at a solution I am completely lost as to what I'm supposed to do here. I would think you'd find the potential at 2A and subtract it from that at the center. But how exactly do you do that? I integrated the elctric field due to a charged sphere along 2A to A. So that makes: ∫E dr= ∫(ρr)/3ε0)dr=V That makes: [(ρr2)/6ε)] from 2A to A which does not equal the answer. I think I'm stumped here. Any help would be greatly appreciated!