First slide

Magnetic Dipole moment

Question

A circular coil of radius 4 cm has 50 turns. In this coil a current of 2 A is flowing. It is placed in a magnetic field of 0.1 weber / $m^{2}$ . The amount of work done in rotating it through 180° from its equilibrium position will be

Moderate

A

0.1 J
B

0.2 J
C

0.4 J
D

0.8 J

Solution

Work done to rotate $W = MB (1 - cosθ)$
When $θ = 180^{o} W = 2 MB$
Here M = niA
W = 2.niAB
$= 2 \times 50 \times 2 \times π {(4 \times 10^{- 2})}^{2} 0 .1$
$= 20 π \times 16 x 10^{- 4}$
$= 32 π \times 10^{- 3} = 100 \times 10^{- 3} = 0 .1 J$

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