Answer: 1/(2πfC).
- A 1/(2πfC)
- B 2πfC
- C C/(2πf)
- D 2πf/C
Correct answer: A. 1/(2πfC)
Explanation: X<sub>C</sub> = 1/(ωC) = 1/(2πfC). X<sub>C</sub> decreases as frequency increases. Capacitors block DC (f=0, X<sub>C</sub> = ∞) but pass high-frequency AC.
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.