Magnetism and Matter - Result Question 6
9. A bar magnet, of magnetic moment $\vec{M}$, is placed in a magnetic field of induction $\vec{B}$. The torque exerted on it is
(a) $\vec{M} \cdot \vec{B}$
(b) $-\vec{M} \cdot \vec{B}$
(c) $\vec{M} \times \vec{B}$
(d) $\vec{B} \times \vec{M}$
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Answer:
Correct Answer: 9. (c)
Solution:
- (c) We know that when a bar magnet is placed in the magnetic field at an angle $\theta$, then torque acting on the bar magnet $(\tau)$
$=M B \sin \theta=\vec{M} \times \vec{B}$.
The direction of torque $(\tau)$ is perpendicular to the plane containing $M$ and $B$ and is given by right hand screw rule.
