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A bar magnet having a magnetic moment of...

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.

A

`0.2 J`

B

`0.1 J`

C

`0.4 J`

D

`0.3 J`

Text Solution

Verified by Experts

The correct Answer is:
A
the work done by the external agent `=` change in potential energy
`= - (MB cos theta_(2)) - (-MB cos theta_(1))`
`= - MB (cos 60^(@) - cos 0^(@)) = (1)/(2) MB`
`= (1)/(2) (1.0 xx 10^(4) J//T) (4 xx 10^(-5)T) = 0.2 J`
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