Two charges -q and +q are located at points (0, 0, -a) and (0, 0, a), respectively. What is the electrostatic potential at the points? Obtain the dependence of potential on the distance r of a point from the origin when r/a >> 1.How much work is done in moving a small test charge from the point (5, 0, 0) to (-7, 0, 0) along the x-axis? Does the answer change if the path of the test charge between the same points is not along the x-axis?