A 250-turns recantagular coil of length 2.1 cm and width 1.25 cm carries a current of `85 muA` and subjected to magnetic field of strength `0.85 T`. Work done for rotating the coil by `180^(@)` against the torque is

Options

A. `9.1 muJ`
B. `4.55 muJ`
C. `2.3 muJ`
D. `1.5 muJ`

Answer

A

Explanation

Work done for rotating the coil
Where, M = magnetic moment B = magnetic field
Give, `theta_(1)=0^(2), theta_(2)=180^(@)`
`rArr W=MB(cos 0^(@)-cos 180^(@))=2MB=2xxNIAxxB`
`=2xx250xx85xx10^(-6)xx(2.1xx1.25xx10^(-4))xx0.85`
`=9.48xx10^(-6)J=9.5xx10^(-6)J=9.5muj`
The closest option is (a)