A bar magnet having a magnetic moment of `1.0 xx 10^4 J T^(-1)` is free to rotate in a horizontal plane. A horizontal magnetic field `B = 4 xx 10^(-5) T` exists in the space. Find the work done in rotating the magnet slowly from a direction parallel to the field to a direction `60^@` from the field.

Options

A. 0.2 J
B. 2 J
C. 4.18 J
D. `2xx10^(2)J`

Answer

A

Explanation

Magnetic moment`=10^(4)J//T`
`B=4xx10^(-5)T,theta=60^(@)`
Work done in moving the magnet in uniform magnetic field.
`W=MB(1-costheta)`
`=10^(4)xx4xx10^(-5)(1-cos60^(@))`
`=0.2J`