Chapter 17, Problem 44P

Torque and force on a dipole. An electric dipole is in a uniform external electric field $\stackrel{\to }{E}$ as shown in Figure 17.52. (a) What is the net force this field exerts on the dipole? (b) Find the orientations of the dipole for which the torque on it about an axis through its center perpendicular to the plane of the figure is zero, (c) Which of the orientations in part (b) is stable, and which is unstable? (Hint: Consider a small displacement away from the equilibrium position, and see what happens.) (d) Show that, for the stable orientation in part (c), the dipole's own electric field opposes the external field for points between the charges.

Figure 17.52

Problem 44.