Answer: 0.
- A 0
- B 0.5
- C 0.707
- D 1
Correct answer: A. 0
Explanation: Current and voltage are 90° out of phase, so cosφ = 0 and average power is zero.
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.