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