1. The problem statement, all variables and given/known data A positive charge +q is located at the point x= 0, y = -a and a negative charge -q is located at the point x=0, y=a (a) Derive an expression for the potential at points on the y-axis as a function of the coordinate y. Take V to be zero at an infinite distance from the charges. 2. Relevant equations ΔV = -∫E⋅dl E= kq/r2 V = kq/r 3. The attempt at a solution I don't understand how my book solved this problem. Can someone explain this solution to me?: http://imgur.com/vIEK7ql [Broken] I understand that the potential is calculated at points between, below, and above the two charges, but how was the final equation produced from the first 3? Some have a's in the numerator while other had y's and they randomly disappeared in the answer. Additionally, is it possible to solve this by finding the electric field of an arbitrary point between the charges then integrating it from that point, y, to infinity with respect to y. I've been given multiple methods of calculating electric potential in my book and I can't seem to figure out which equation is the appropriate one to use. This one seemed like it could be solved using ΔV = -∫E⋅dy, but when I attempted it, it became very complicated. The solution my book provided seem simple, but I'm just not sure what method they are using to obtain the solution.