Answer: 400 W.
- A 400 W
- B 300 W
- C 500 W
- D 250 W
Correct answer: A. 400 W
Explanation: Z = √(40² + 30²) = 50 Ω. Power factor = R/Z = 40/50 = 0.8. Real power = apparent power × PF = 500 × 0.8 = 400 W.
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.