1. The problem statement, all variables and given/known data A pipe that is not a conductor has a uni form charge density 40 C/m^3. The inner radius is 0.15 m and the outer radius is 0.25 m. What is the electric field magnitude at r=0.3 m? 2. Relevant equations Gauss's Law: net flux = int[E*dA] = Q_encl / epsilon naught 3. The attempt at a solution First, I figure to treat this as a cylinder, V = pi*r^2 * L But how would the inner/outer radii come into play? Would it be instead V = pi*r_1^2 * L - pi* r_2^2 * L where r_1 = .25 m (outer radius), r_2 = .15 m (inner radius)? Is that correct so far? What would the area be? For a cylinder, it's 2*pi*r^2 + 2*pi*r*L, but then L wouldn't totally cancel out, right?