A bar magnet having a magnetic moment of `2 xx 10^4 JT^(-1)` is free to rotate in a horizontal plane. A horizontal magnetic field `B = 6 xx 10^(-4)` T exists in the space. The work done in taking the magnet slowly from a direction parallel to the field to a direction `60^@` from the field is

Options

A. 0.6J
B. 12J
C. 6J
D. 2J

Answer

C

Explanation

`W= Delta U= - MB (cos theta_(f)- cos theta_(i))`
`= -2 xx 10^(4) xx 6 xx 10^(-4) (cos 60- cos 0^(@))= 6J`
= +6 J