Moving Charges And Magnetism Ques 55
55. 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
[2017]
(a) $4.55 $ $\mu J$
(c) $1.15 $ $\mu J$
(b) $2.3 $ $\mu J$
(d) $9.1 $ $\mu J$
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Answer:
Correct Answer: 55.(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 $ $\mu J$
BETA
