Answer: 1/(2pi f C).
- A f C
- B 2pi f C
- C 1/(2pi f C)
- D C/f
Correct answer: C. 1/(2pi f C)
Explanation: Capacitive reactance Xc = 1/(2 pi f C) = 1/(omega C). Impedance of pure capacitor = Xc.
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.