Question

What is the potential energy of a dipole in unstable equilibrium in a uniform electric field?

Options

• U = pE/2

• U = 0

• U = -pE

• U = +pE

Answer 1

In unstable equilibrium at θ = 180°, the dipole is anti-parallel to the field. The potential energy is U = -pE cos(180°) = -pE × (-1) = +pE, which is the maximum possible value. This high potential energy represents an unstable state.