A positive point charge +Q?is at the origin, and a dipole of moment p?is a distance r?away and in the radial direction as in Figure.

(a) Show that the force exerted by the electric field of the point charge on the dipole is attractive and has a magnitude of approximately 2kQp/r³ (see Problem 55).

(b) Now assume that the dipole is centered at the origin and that a point charge Q?is a distance r?away along the line of the dipole. From your result for part (a) and Newton's third law, show that the magnitude of the electric field of the dipole along the line of the dipole a distance r?away is approximately 2kp/r³.