Here, θ=30°,τ=0.018N−m,B=0.06T Torque on a bar magnet : τ=MBsinθ 0.018=M×0.06×sin30° ⇒0.018=M×0.06×
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⇒M=0.6A−m2 Position of stable equilibrium (θ=0°) Position of unstable equilibrium (θ=180°) Minimum work required to rotate bar magnet from stable to unstable equilibrium ΔU=Uf−Ui=−MBcos180°−(−MBcos0°) W=2MB=2×0.6×0.06 ∴W=7.2×10−2J