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^(@))`
`= 0.096 pi xx 0.2 J`
`=0.06 J`