Question

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. $M+B$

Answer 1

The correct option is A $M\times B$

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 is the length and b the distance
the term $ilb=M=$ dipole moment
$\tau =MB\sin \theta$
$\tau =M\times B$