Question

A rectangular coil is placed in a uniform magnetic field directed in its plane and parallel to one of its sides. The graph of $\tau vs\theta$ will be:
$(\theta$ is angular displacement of coil$)$

• A.
• B.
• C.
• D.

Answer 1

The correct option is A

Torque acting on the coil is

$\tau =MB\sin \theta$

Variation in torque is given by,

${\tau }_{max}=MB$ (when $\theta ={90}^{\circ })$

${\tau }_{min}=0$ (when $\theta =0^{\circ }$ and ${180}^{\circ })$

And the graph will be a sine curve due to the term $\sin \theta$.

Therefore, correct answer will be option $\left(A\right)$.