Two point charges q and - q are located at points (0 , 0 , - a ) and (0 , 0 , a) respectively :
(a) Find the electrostatic potential at (0 , 0 , z) and ( x, y , 0).
(b) 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 ?
(c) How would your answer change if the path of the test charge between the same points is not along the x axis but along any other random path ?
(d) If the above point charges are now placed in the same position in a uniform external electric field `vecE` , what would be the potential energy of the charge system in its orientation of unstable equilibrium ? Justify your answer in each case .