A closely wound solenoid has 2000 turns, cross-sectional area 1.5 × 10⁻⁴ m² and carries current 2.0 A. Suspended about its centre, it is in a uniform horizontal magnetic field of 5 × 10⁻² T making 30° with the solenoid axis. Find the torque.
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Question

A closely wound solenoid has 2000 turns, cross-sectional area 1.5 × 10⁻⁴ m² and carries current 2.0 A. Suspended about its centre, it is in a uniform horizontal magnetic field of 5 × 10⁻² T making 30° with the solenoid axis. Find the torque.

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G1 Physics · Accepted Answer

Step 1: Given N=2000 turns, A=1.5×10⁻⁴m², I=2.0A, B=5×10⁻²T and angle θ=30° between coil axis and B. Step 2: Magnetic moment μ=NIA=(2000)(2.0)(1.5×10⁻⁴)=0.60 A·m². Step 3: Torque magnitude τ=μBsinθ = (0.60)(5×10⁻²)(sin30°) = 0.60×0.05×0.5=0.015N·m. Step 4: Final answer C: 1.5×10⁻²N·m. Final answer: (C) 1.5 × 10⁻² N·m.