Answer: 0.60.
- A 0.50
- B 0.80
- C 0.75
- D 0.60
Correct answer: D. 0.60
Explanation: The supply voltage is V = √(30<sup>2</sup> + 40<sup>2</sup>) = 50 V. The power factor is V<sub>R</sub>/V = 30/50 = 0.60.
In a pure inductor the current lags the voltage by 90° (energy is briefly stored in the magnetic field before current responds); in a pure capacitor the current leads the voltage by 90° (current must flow to build up charge before voltage rises) - the mnemonic "ELI the ICE man" keeps these straight.
Concept context
AC circuits, impedance, LCR series circuit, resonance, transformers, and power factor.