A galvanometer coil has 500 turns and each turn has an average area… | JEE Main 2020 (3 Sep, Shift 2)

Q60JEE Main 2020 · 3 SEP · SHIFT 2Easy

Current Loop as a Magnetic Dipole

A galvanometer coil has 500 turns and each turn has an average area of 3 $\times$ 10–4 m2. If a torque of 1.5 Nm is required to keep this coil parallel to a magnetic field when a current of 0.5 A is flowing through it, the strength of the field (in T) is ______.

Numerical answer type. Work it out, then open the answer.

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Answer: 20

Torque on a coil: $\tau = NIAB\sin\theta$ , where $\theta$ is the angle between the coil's normal and $\vec{B}$ .
Coil plane parallel to $\vec{B}$ means the normal is perpendicular to it, so $\theta = 90^\circ$ and $\tau = NIAB$ .
$B = \frac{\tau}{NIA} = \frac{1.5}{500 \times 0.5 \times 3\times10^{-4}} = \frac{1.5}{0.075}$
So $B = 20$ T.

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