Answer: Current leads voltage by 90°.
- A Current leads voltage by 90°
- B Current lags voltage by 90°
- C Current and voltage are in phase
- D Current leads voltage by 45°
Correct answer: A. Current leads voltage by 90°
Explanation: For a pure capacitor, I = C(dV/dt). The current leads the voltage by 90° (π/2 rad).
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.