Moving Charges and Magnetism - Result Question 57
58. A 250-turn rectangular coil of length $2.1 cm$ and width $1.25 cm$ carries a current of $85 \mu A$ and subjected to magnetic field of strength 0.85 T. Work done for rotating the coil by $180^{\circ}$ against the torque is
(a) $4.55 \mu J$
(c) $1.15 \mu J$
(b) $2.3 \mu J$
(d) $9.1 \mu J$
[2017]
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Answer:
Correct Answer: 58. (d)
Solution:
- (d) Work done, $W=MB(\cos \theta_1-\cos \theta_2)$
When it is rotated by angle $180^{\circ}$ then
$W=MB(\cos 0^{\circ}-\cos 180^{\circ})=MB(1+1)$
$W=2 MB$
$W=2$ (NIA) B
$=2 \times 250 \times 85 \times 10^{-6}[1.25 \times 2.1 \times 10^{-4}] \times 85 \times$
$10^{-2}$
$=9.1 \mu J$
