A magnetic dipole of moment M is placed exactly antiparallel to a uniform magnetic field B.
Which statement is correct?

Question

A magnetic dipole of moment M is placed exactly antiparallel to a uniform magnetic field B. Which statement is correct?

G1 Physics · Accepted Answer

Magnetic potential energy is U = -MB cosθ. For antiparallel orientation, θ = π. Therefore, U = -MB cosπ = +MB. This is the maximum possible magnetic potential energy. Also, τ = MB sinπ = 0, so the configuration is an equilibrium position. Since a small displacement lowers the potential energy, the equilibrium is unstable. Hence option B is correct.