Two charges - q and +q are located at points (0, 0, - a) and (0,0, a), respectively.
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 ?

Explanation

The given charges behave as an electric dipole and the dipole length is 2a, hence dipole moment `p = q.2a`.
As the motion of test charge from the point (5, 0, 0) to (-7,0,0) is along x-axis and electric potential is only along z-axis, hence work done = 0.
The answer does not change because the electric field is a conservative field and the work done simply depends on the position of initial and final points only.