The work done in turning the dipole through a small angle dθ is

dW = τ dθ = MB sinθ dθ

If the dipole is rotated from initial position θ₁ to θ₂, then total work done is

This is stored as potential energy.

The P.E. of the dipole is zero when m is perpendicular to B and if θ₁ = 90°, θ₂ = θ then

U = - MB (cosθ – Cos90)

Special cases:

1. θ = 0⁰, then U = -MB, thus the P.E. of a dipole is minimum when M is parallel to B. in this, the magnetic dipole is in stable equilibrium.
2. When θ = 90⁰ , U = 0
3. When θ = 180⁰ , U = MB, thus the P.E. of a dipole is minimum in this , the magnetic dipole is in unstable equilibrium.