(a) Two identical point charges + q are located on the y -axis at y = + a and y = − a. What is the electric field along the x -axis at x = b?
(b) A circular ring of charge of radius a has a total positive charge Q distributed uniformly around it. The ring is in the x = 0 plane with its center at the origin. What is the electric field along the x - axis at x = b due to the ring of charge? [Hint: Consider the charge Q to consist of many pairs of identical point charges positioned at the ends of diameters of the ring.]