# A magnetic dipole in a constant magnetic field has : Option 1) maximum potential energy when the torque is maximum. Option 2)  zero potential energy when the torque is minimum. Option 3)  zero potential energy when the torque is maximum. Option 4)  minimum potential energy when the torque is maximum.

As we learnt in

Torque -

$\underset{T}{\rightarrow}=\underset{M}{\rightarrow}\times \underset{B}{\rightarrow}=M=NiA$

T=$MB\sin \theta =NBiA\sin \theta$

- wherein

M - magnetic moment

Work done by current carrying coil -

$W=MB(1-\cos \theta )$

-

For maximum torque $\theta=90^{o}$ and for this value of $\theta$ potential energy will be zero..

Correct option is 3.

Option 1)

maximum potential energy when the torque is maximum.

Incorrect

Option 2)

zero potential energy when the torque is minimum.

Incorrect

Option 3)

zero potential energy when the torque is maximum.

Correct

Option 4)

minimum potential energy when the torque is maximum.

Incorrect

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