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A bar magnet is placed in a uniform magn...

A bar magnet is placed in a uniform magnetic field with its magnetic moment making an angle `theta` with the field. Write expressions for torque on the bar magnet and potential energy of magnet in this orientation. When it this energy minimum?

Text Solution

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`tau=MB sin theta`
`P.E.=-MB cos theta` when `theta=0`,
`P.E.=-MB cos 0^@=-MB=minim um`
Thus, `P.E.` of magnet is minimum when its magnetic moment `vecM` is aligned parallel to the field `vecB`.
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