What am I doing wrong here? Here's the problem: For the arrangement descripbed in the previous problem (see attachment), calculate the electric potential at point B that lies on the perpendicular bisector of the rod a distance b above the x axis. [lamb] = [alpha] x where [alpha] is a constant. The correct answer is V = -(k[alpha]L/2)ln(([squ] [(L^2/4) + b^2)] - L/2)/[squ] [(L^2/4) + b^2)] - L/2)) I'm not getting the same answer. So far I've got the following: [the] = [<]'a' on the diagram. V = kq/r x' = btan[the] dx' = bsec^2[the]d[the] x = L/2 + x' r = bsec[the] dq = [lamb]d(L/2 + x') = [lamb]dx' dq = [alpha](L/2 + x')dx' = [alpha](L/2 + btan[the])bsec^2[the]d[the] so dV = k[alpha](L/2 + btan[the])bsec^2[the]d[the]/bsec[the] Taking the integral of both sides from -[the] to +[the] doesn't yield the correct result. I'd appreciate it if someone could point out where I went wrong. I have a feeling the problem's in [lamb] = dq/dL = dq(L/2 + x'). Thanks.