A bar magnet having a magnetic moment of `2xx10^(4) JT^(-1)` is free to rotate in a horizontal plane. A horizontal magnetic field `B=6xx10^(-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 isA. `0.6J`B. `12J`C. `6J`D. `2J`

A bar magnet having a magnetic moment of `2xx10^(4) JT^(-1)` is free t

1.	A bar magnet having a magnetic moment of `2xx10^(4) JT^(-1)` is free to rotate in a horizontal plane. A horizontal magnetic field `B=6xx10^(-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 isA. `0.6J`B. `12J`C. `6J`D. `2J`
Answer» Correct Answer - C The work done in rotating a magnetic dipole against the torque acting on it, when placed in magnetic field is stored inside it in the form of potential energy. When magnetic dipole is rotated from intial position `theta=theta_(1)` to final position `theta=theta_(2)`, then work done `=MB(costheta_(1)-costheta_(2))` `= MB(1-(1)/(2)) = (2 xx 10^(4) xx 6 xx 10^(-4))/(2) = 6 J`

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