For a moving coil galvanometer, the deflection in the coil is 0.05 rad when a current of 10 mA is passed through it. If the torsional constant of suspension wire is 4.0 × 10⁻⁵ N m rad⁻¹, the magnetic field is 0.01 T and the number of turns in the coil is 200, the area of each turn (in cm²) is :
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Question

For a moving coil galvanometer, the deflection in the coil is 0.05 rad when a current of 10 mA is passed through it. If the torsional constant of suspension wire is 4.0 × 10⁻⁵ N m rad⁻¹, the magnetic field is 0.01 T and the number of turns in the coil is 200, the area of each turn (in cm²) is :

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G1 Physics · Accepted Answer

For equilibrium, magnetic torque = restoring torque: NIAB = Kθ. Therefore A = Kθ/(NIB) = (4.0 × 10⁻⁵ × 0.05)/(200 × 10 × 10⁻³ × 0.01) = 1.0 × 10⁻⁴ m² = 1.0 cm².