An electric dipole is released from rest in a uniform electric field with the orientation shown. Which entry in the table below correctly describes the net torque and the net force on the dipole?

Question

Quizplus · Accepted Answer

The electric dipole experiences a torque because of the orientation of the dipole moment vector relative to the electric field. The torque is given by τ = pEsinθ, where p is the dipole moment and θ is the angle between p and E. In this case, the dipole moment is perpendicular to the electric field, so the angle θ is 90° and sinθ = 1. Therefore, the torque is maximum and given by τ = pE.
 
Since the electric field is uniform, the force on the positive charge is in the direction opposite to the electric field, and the force on the negative charge is in the direction of the electric field. The magnitudes of the two forces are equal, and they form a couple that produces the torque on the dipole. The net force on the dipole is zero, since the forces on the two charges are equal and opposite.

Therefore, the correct choice is B, which says that the net torque is non-zero and the net force is zero.

An Electric Dipole Is Released from Rest in a Uniform