An AC circuit with a 30 Ω resistor and 60 mH inductor in series is connected to a 100 V (rms) source. At what frequency is the power factor 0.707?
Correct answer: B. 79.6 Hz
- A. 50 Hz
- B. 79.6 Hz
- C. 100 Hz
- D. 159.2 Hz
Explanation
Power factor cos φ = 0.707 implies φ = 45°, so XL = R = 30 Ω. XL = ωL = 2πf × 0.06 = 30, f = 30 / (2π × 0.06) ≈ 30 / 0.377 ≈ 79.6 Hz.
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