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A closely wound solenoid of 800 turns and area of cross section 2.5 × 10⁻⁴ m² carries a current of 3.0 A. The magnetic moment associated with it is ________.

Asked in GUJCET 2026 · Magnetic moment of loops and charges

Answer: (3) 0.60 JT⁻¹

Step-by-step solution

Given: N=800 turns, A=2.5×10⁻⁴ m², I=3.0 A.

Idea: each turn is a current loop of moment IA, and in a closely wound solenoid every turn points the same way, so the moments simply add: m=NIA.

800×3.0=2400 A of total current linking the cross-section.

m=2400×2.5×10⁻⁴=0.60 J T⁻¹, directed along the axis of the solenoid — which is why it behaves like a bar magnet.

Why the other options are wrong

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