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 mu J`
B. ` 4.55 mu J`
C. `2.3 muJ`
D. `1.15 muJ`

Answer

A

Explanation

`W=MB(cos theta_(1)- cos theta_(2))`
When it is rotated by angle `180^(@)` then
W=2MB
W =2(NIA) B
`=2xx250xx85xx10^(-6)[1.25xx2.1xx10^(-4)]xx85xx10^(-2)`
`=9.1 muJ`