A ring-shaped conductor with radius a = 2.50 cm has a total positive charge Q = + 0.125 nC uniformly distributed around it, as shown in Fig. 21.24. The center of the ring is at the origin of coordinates 0.
(a) What is the electric field (magnitude and direction) at point P, which is on the x-axis at x = 40.0 cm?
(b) A point charge q = - 2.50 µC is placed at the point P described in part (a). What are the magnitude and direction of the force exerted by the charge q on the ring?