A bar magnet is hung by a thin cotton thread in a uniform horizontal magnetic field and is in equilibrium state. The energy required to rotate it by 60° is W. Now the torque required to keep the magnet in this new position is
A
√3W2
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B
2W√3
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C
W√3
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D
√3W
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Solution
The correct option is D√3W
Torque acting on the magnet is,τ=MBsin60°_________(1)Workdonecanbewrittenas,W=MB(1−cos60°)____(2)From(1)and(2)τW=√3/21/2⇒τ=W√3