A circular coil of 60 turns and radius 4 cm carries current of 1 A . How much work will be done in rotating the coil through `90^(@)` . It is suspended freely in uniform magnetic field `0.2 T`.

Explanation

`M =NiA`
` = 60 xx 1 xx pi xx (0.04) ^(2)`
`= 60 pi xx 16 xx 10 ^(-4)`
` = 960 xx 10 ^(-4) pi`
`= 0.096 pi Am^(2)`
`W = MB (cos theta _(1) - cos theta _(2))`
`theta_(1) = 0^(@) , theta _(2) =90^(@)`
`W = 0.096 pi xx 0.2 xx (cos 0^(@) - cos 90^(@))`
`=.096 pi xx 0.2J`
`= 0.06J`