A magnetic needle lying parallel to the magnetic field requires W units of work to turn it through an angle 45 o . The torque required to maintain the needle in this position will be

Question

A magnetic needle lying parallel to the magnetic field requires W units of work to turn it through an angle 45 o . The torque required to maintain the needle in this position will be, 2 W, 1 3 W, 2 - 1 W, W 2 - 1

MARKS App · Accepted Answer

Work done by a magnet to turn from angle θ 1 t o θ 2 is W = B cos ⁡ θ 1 - c o s θ 2 = M B 1 - 1 2 = 2 - 1 2 M B Also torque acting on the magnet is given by τ = M B sin ⁡ 45 o = M B 2 So W = 2 - 1 ⋅ τ ∴ τ = W 2 - 1

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