A rectangular coil of effective area 0.04 m ² is suspended freely in a radial magnetic field of 0.02 Wb/m ². The torsional constant of the suspension fibre is 5 × 10⁻⁹ Nm/degree. If a current of 250 μ A is passed through it, then the angle through which it rotates is (a) 30° (b) 40° (c) 45° (d) 50°

Answer: (b). In a radial field: kθ = NBAI, so θ = BAI/k (effective area includes N). θ = 0.02 × 0.04 × 250×10⁻⁶5×10⁻⁹ = 2×10⁻⁷5×10⁻⁹ θ = 40° So the answer is (b) 40°.

A rectangular coil of effective area 0.04 m ² is suspended freely in… | MHT CET 2026 (19 May, Shift 1)

Q7MHT CET 2026 · 19 MAY · SHIFT 1Medium

Moving Coil Galvanometer, Ammeter & Voltmeter

A rectangular coil of effective area $0.04$ m $^{2}$ is suspended freely in a radial magnetic field of $0.02$ Wb/m $^{2}$ . The torsional constant of the suspension fibre is $5 \times 10^{-9}$ Nm/degree. If a current of $250\ \mu$ A is passed through it, then the angle through which it rotates is

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Answer: (b)

In a radial field: $k\theta = NBAI$ , so $\theta = \frac{BAI}{k}$ (effective area includes $N$ ).
$\theta = \frac{0.02 \times 0.04 \times 250\times10^{-6}}{5\times10^{-9}} = \frac{2\times10^{-7}}{5\times10^{-9}}$
$\theta = 40^\circ$
So the answer is (b) $40^\circ$ .

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