Q.

A magnetic dipole experiences a torque of 803 Nm when placed in uniform magnetic field in such a way that dipole moment makes angle of 60° with magnetic field. The potential energy of the dipole is:         [2025]

1 80 J  
2 –403 J  
3 –60 J  
4 –80 J  

Ans.

(4)

|τ→|=|M→×B→|=MB sin 60°

803=32MB ⇒ MB=160

U=–M→·B→=–MB cos 60°

U=–160×12=–80 J