1. The problem statement, all variables and given/known data Solid ball of charge with radius R and volume charge density ρ(r) = ρ0r2, centred at the origin. I have already found the electric field for r<R and r>R and also the potential at the origin by using the formula: V = -∫E.dl Now i want to find the potential at the origin using the charge density but am at a loss for the first step 2. Relevant equations V = (1/4∏ε)∫(ρ/r)d[itex]\tau[/itex] 3. The attempt at a solution I don't need the full solution, just the first step would be much appreciated.