An insulating rod of length l is bent into a circular arc of radius R that subtends an angle theta from the center of the circle. The rod has a charge Q ditributed uniformly along its length. Find the electric potential at the center of the circular arc. Struggling with this problem. I know that I have to divide the charge Q into many very small charges, essentially point charges, then sum them up (integration). dV = dq/(4 Π Ε0 R) Length of dq = ds db = angle subtended by ds dΒ=ds/R => ds = dBR dq = λds => dq = λdBR V = ∫ dq/(4 Π Ε0 R) V = ∫ λdBR/(4 Π Ε0 R) Now, this is where it all goes wrong for me. I take out the constants V = λR/(4 Π Ε0 R) * ∫ dB My Rs cancel out, which makes no sense. The radius must be important in the calculation of the difference potential. Notice also that I did not indicate the limits on the integration. In a similar problem which was done in a previous assignemnt to calculate the electric field at the center, the upper and lower limits were set to -B/2 and B/2, but I am not sure why.