Capacitive Reactance
The opposition offered by a capacitor to alternating current flow, inversely proportional to AC frequency and capacitance.
Governing formula
X_C = 1 / (2π f C) = 1 / (ω C)
SI unit
Ω (Ohms)
In depth
Capacitors block steady DC current completely (f = 0 ⇒ X_C = ∞), but pass high-frequency AC signals with very low opposition (f → ∞ ⇒ X_C → 0).
Examples in the real world
DC-blocking coupling capacitors in audio preamplifiers passing high-frequency music signals while isolating DC bias voltages.