1. The problem statement, all variables and given/known data Three point charges each of 4 µC are situated at the three corners of an equilateral triangle of side 4 m. Find the work done in moving one of them to a point mid-way between the other two. Solution: The Potential diﬀerence VAB between two points A and B is the work done in moving a unit positive charge from A to B. The work done in moving a test charge q from A to B is WAB = qVAB. First let us assume that the side of the triangle is a and later we can substitute a number for it. VAB = 2 * [q / (4πε0) * (2/a −1/a)] = 2q / (4πε0a) = 72 / s kV 2. Relevant equations V = q / (4πε0r) W = qVAB 3. The attempt at a solution I have the solution part of it is shown above. The answer is 72 mJ. I think I understand it but am having trouble convincing myself with regaurds to portion of the solution shown above. I need some conceptual assistance. Here is what I am seeing. Lets make an equilateral triangle with a charge q1 at the origin, q2 at (4,0), and q3 at (2,2sqrt(3)) I belive VA at q3 = 2 * q / (4πε0a) where a is the radius (defined in the solution) I belive VB at (2,0) when moving q3 down = 2 * q / (4πε0(a/2)) = q / (πε0a) Then VAB = VB - VA = q / (πε0a) - 2 * q / (4πε0a) = 2q / (4πε0a) This is the solution I am looking for but I want to make sure my reasoning is sound. My equation is equivalent to but is not set up like the one in the solution. The way the solution shows it in step 1 seems like an odd way to express it. I am also having trouble convincing myself of this result because q3 is a point charge and not just some test point. I want ta say that there must be a voltage created by q3 and that my math has neglected to account for it. Any help is greatly appreciated. It is exam day tomorrow and I don't want to blow it on lack of conceptual understanding.