electric potential
posted by Jeff .
Given a square of side length a = 6 cm. We place a charged particle at each corner, three of them carry +7 nC of charge and one carries the same amount of negative charge. What is the electric potential at the center of the square? Choose V = 0 V for a position very far from the square.

electric potential is a scalar, so you add each.
V= kq1/d+kq2/d + ... notice the negative just cancels from one of the positive.
= 14E9 * k/d where d= 1/2 diagonal length.
Dealing with scalars is nice.