The magnetic moment of an iron bar is M. It is bent to form an arc of a circle subtending 60° at its centre. The magnetic moment of the arc section is:
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Question

The magnetic moment of an iron bar is M. It is bent to form an arc of a circle subtending 60° at its centre. The magnetic moment of the arc section is:

G1 Physics · Accepted Answer

Step 1: Magnetic moment M = mℓ, where m is pole strength and ℓ is original straight length. Step 2: Arc length ℓ = rθ; θ = 60° = π/3 rad. New pole separation is chord 2r sin(θ/2) = r. Step 3: New moment M′ = mr = M(r/ℓ) = M/θ = 3M/π (option A). Final answer: (A) 3M/π.