A magnetic needle suspended parallel to a magnetic field requires 3 J of work to turn it through 6 0 ∘ . The torque needed to maintain the needle in this position will beNEET 2012 (Mains)

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A magnetic needle suspended parallel to a magnetic field requires 3 ​ J of work to turn it through 6 0 ∘ . The torque needed to maintain the needle in this position will beNEET 2012 (Mains)

TestHub · Accepted Answer

In this case, work done W MB τ ​ = MB ( cos θ 1 ​ − cos θ 2 ​ ) = MB ( cos 0 ∘ − cos 6 0 ∘ ) = MB ( 1 − 2 1 ​ ) = 2 MB ​ = 2 3 ​ J ( ∵ given W = 3 ​ J ) = MB sin 6 0 ∘ = ( 2 3 ​ ) ( 2 3 ​ ​ ) J = 3 J ​

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