A bar magnet is suspended by a string in a uniform magnetic field making an angle of 60o with the field. Torque required to hold the magnet in that position is 25×10−3 N−m. Then the work done by an external agent to rotate the magnet clockwise through an angle of 90o is (Take 3=1.7)
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a
1.50 J
b
zero
c
0.25 J
d
0.01 J
answer is D.
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Detailed Solution
τ=MBsin60o⇒MB=2τ3Now Ui=−MBcos60o=−τ3 and Uf=−MB(90o−60o)=−τ∴ W=Uf−Ui==−τ−(−τ3)=−(3−13)τ=0.01 J
A bar magnet is suspended by a string in a uniform magnetic field making an angle of 60o with the field. Torque required to hold the magnet in that position is 25×10−3 N−m. Then the work done by an external agent to rotate the magnet clockwise through an angle of 90o is (Take 3=1.7)