1. The problem statement, all variables and given/known data A plastic circular washer is cut in half and has a charge Q spread uniformly over it. If the electrical potential at infinity is taken to be zero, what is the electric potential at the point P, the center of the old washer? The inner radius of the washer is a, the outer radius is b. *see attached picture* 2. Relevant equations I know that you can use ∫∫E⋅dA=Q/ε and solve for E. Then V(r)=∫E(r)dr 3. The attempt at a solution ∫∫E⋅dA=Q/ε E∫∫dA=Q/ε ∫∫dA=πb^2-πa^2 E(πb^2-πa^2)=Q/ε E=Q/ε(πb^2-πa^2) Then I integrated this, but the answer is V=Q/2πε(b+a) which is not what I am getting. Where am I going wrong?