Question

When a dipole rotates from θ = 0° to θ = 90° in a uniform electric field, how does its potential energy change?

Options

• Decreases from -pE to zero

• Increases from zero to +pE

• Increases from -pE to zero

• Remains constant at -pE

Answer 1

The potential energy of a dipole is U = -pE cos θ. At θ = 0°, U = -pE (minimum). At θ = 90°, U = -pE cos(90°) = 0. Therefore, as the dipole rotates from parallel (θ = 0°) to perpendicular (θ = 90°) to the field, its potential energy increases from -pE to zero.