1. The problem statement, all variables and given/known data There is a thin rod with charge Q that has been bent into a semicircle with radius R. Find an expression for the electric potential at the center. Radius = R Charge = Q 2. Relevant equations V = ∫(k * dq)/r 3. The attempt at a solution dq = λdx λ = Q/L L = pi * r V = kQ / LR ∫ dx = kQ / pi * r^2 ∫ [3pi/2 - pi/2] V = kQ/R^2 But the answer should be kQ/R. How did the other R get cancelled?