question_answer

A bar magnet of magnetic moment M is placed in the magnetic field B. The torque acting on the magnet is.

A)  \[M\times B\]  

B)  \[M-B\]   

C)  \[\frac{1}{2}M\times B\]

D)  \[M+B\]

Correct Answer: A

Solution :

 Torque is equal to instantaneous moment of deflecting couple . The torque acting is given by \[\tau =\] force\[({{F}_{1}}={{F}_{2}})\times \] perpendicular distance \[\tau =iBl\times b\sin \theta \] Where\[i\]is current, B is magnetic field,\[l\]the length and b the distance the term\[ilb=M=\]dipole moment \[\tau =MB\,sin\theta \] \[\tau =M\times B\]