If the magnet be rotated from an initial orientation θ1=0∘ to final orientation θ2=180∘ the total work done W=
∫
θ1
θ2MB‌sin‌d‌θ =MB[−cos‌θ]θ1θ2 =MB(cos‌θ1−cos‌θ2) where B= magnetic field induction M = magnetic moment =MB(+cos‌0∘−cos‌180∘) =MB[1+1]=2MB