A) \[-MB\text{ }(1-cos\text{ }90{}^\circ )\]
B) \[-MB(cos\text{ }60{}^\circ -cos\text{ }90{}^\circ )\]
C) \[-MB(0cos\text{ }60{}^\circ )\]
D) \[-MB(sin\text{ }60{}^\circ -cos\text{ }90{}^\circ )\]
Correct Answer: C
Solution :
We knows, work done in rotating a magnet of magnetic moment M in magnetic field of strength B from angle\[{{\theta }_{1}}\]and\[{{\theta }_{2}}\]is \[W=-\text{ }MB(cos\text{ }{{\theta }_{2}}-cos\text{ }{{\theta }_{1}})\] Here given\[{{\theta }_{1}}=60{}^\circ \]and\[{{\theta }_{2}}=90{}^\circ \] Hence \[W=-MB(\cos 90{}^\circ -\cos 60{}^\circ )\] \[W=-MB(0-\cos 60{}^\circ )\]
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