Answer: In phase for pure resistor only.
- A Always in phase
- B Always out of phase
- C In phase for pure resistor only
- D Depends on frequency only
Correct answer: C. In phase for pure resistor only
Explanation: In a pure resistor, V and I are in phase. In inductors or capacitors, they are out of phase.
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.