Answer: The component of current 90° out of phase with voltage that does no work.
- A The component of current 90° out of phase with voltage that does no work
- B The current flowing specifically at the resonant frequency in the majority of cases studied
- C The total instantaneous current supplied by the AC source as widely reported
- D The steady DC offset component superimposed on the AC current in standard practice
Correct answer: A. The component of current 90° out of phase with voltage that does no work
Explanation: Wattless (reactive) current is the component 90° out of phase with voltage. It oscillates back and forth between source and reactance (L or C) doing no net work.
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.