1. The problem statement, all variables and given/known data A long metal cylinder with radius a is supported on an insulating stand on the axis of a long, hollow metal tube with radius b. Thew positive charge per unit length on the inner cylinder is [tex]\lambda[/tex], and there is an equal negative charge per unit length on the outer cylinder. Calculate the potential for r < a; a < r < b; r > b. 2. Relevant equations EA=q/epsilon Va - Vb = [tex]\int[/tex]E.dl 3. The attempt at a solution I really just need help figuring out why the answer for when r < a is: [(lambda)/(2(pi)(epsilon))]*[ln(b/a)] The reference point here is b. If we are looking for the potential INSIDE the smaller cylinder with radius a, then why are we only integrating from b to a? Shouldn't it be from b to 0? Or is the potential inside the smaller cylinder constant? Why would that be?