1. The problem statement, all variables and given/known data The charge desnsity within a uniformly charged sphere of radius R is ρ = ρ0 - ar2, where ρ0 and a are constants and r is the distance from the center. Find an expression for a such that the electric field outside the sphere is zero. 2. Relevant equations Electric Field outside a sphere E = KQ/r2 3. The attempt at a solution I'm having trouble setting up this problem, I'm not quite sure where to start. If someone could help me I would very much appreciate it.