Answer: Vrms × Irms × cos(φ).
- A Vrms × Irms × cos(φ)
- B Vpeak × Ipeak
- C Vrms × Irms
- D Vpeak × Ipeak / 2
Correct answer: A. Vrms × Irms × cos(φ)
Explanation: Pavg = Vrms × Irms × cos(φ). The factor cos(φ) is the power factor. Only the resistive component dissipates power.
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.