When the dipole moment of a dipole in a uniform electric field rotates to become more nearly aligned with the field:
A)the field does positive work and the potential energy increases
B)the field does positive work and the potential energy decreases
C)the field does negative work and the potential energy increases
D)the field does negative work and the potential energy decreases
E)the field does no work

Question

Quizplus · Accepted Answer

As the dipole moment rotates to become more aligned with the electric field, the angle between them decreases. This means that the dot product of the dipole moment and the electric field vectors increases, which in turn means that the work done by the field is positive. According to the definition of potential energy as the work done by an external force to bring a system from an initial to a final configuration, the potential energy of the dipole increases as it rotates to align more with the field, hence the potential energy decreases. Therefore, choice B is the correct answer.

When the Dipole Moment of a Dipole in a Uniform