# A circular coil having N turns and radius r carries a current I. It is held in the XZ plane in a magnetic field $B\widehat{i}$. The torque on the coil due to the magnetic field is :  Option 1)$\frac{B\pi r^{2}I}{N}$Option 2)$B \pi r^{2}I\; N$Option 3)$\frac{B r^{2}I}{\pi\: N}$  Option 4)$Zero$

$\vec{B}$ is along $x$

$M= NIA$

$M$ is along $y$

$\tau=M\times B=MB\; \sin \; 90=MB$

$\tau=NI(\pi\: r^{2})B$

$\tau=B\pi r^{2}I\; N$

Option 1)

$\frac{B\pi r^{2}I}{N}$

Option 2)

$B \pi r^{2}I\; N$

Option 3)

$\frac{B r^{2}I}{\pi\: N}$

Option 4)

$Zero$

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