A coil of negligible resistance is connected in series with 90 Ω resistor across 120 V, 60 Hz supply. A voltmeter reads 36 V across resistance. Inductance of the coil is:
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A coil of negligible resistance is connected in series with 90 Ω resistor across 120 V, 60 Hz supply. A voltmeter reads 36 V across resistance. Inductance of the coil is:

G1 Physics · Accepted Answer

Voltage across resistor: V(R) = I(rms)R Therefore: I(rms) = 36/90 = 0.4 A Supply voltage: V = 120 V For series RL circuit: V² = V(R)² + V(L)² Therefore: V(L) = √(120² - 36²) ≈ 114.47 V Inductive reactance: X(L) = V(L)/I(rms) ≈ 114.47/0.4 ≈ 286.18 Ω Now: X(L) = 2πfL Therefore: L = 286.18/[2π × 60] ≈ 0.76 H