Inductive Reactance
Inductive reactance rises with frequency and inductance.
XL = 2πfL
An ideal inductor has impedance +jXL, so current lags voltage by 90 degrees.
Capacitive Reactance
Capacitive reactance falls as frequency or capacitance increases.
XC = 1 ÷ (2πfC)
An ideal capacitor has impedance -jXC, so current leads voltage by 90 degrees.
LC Resonance
Ideal series or parallel LC relationships reach resonance when inductive and capacitive reactance magnitudes are equal.
f0 = 1 ÷ (2π√LC)
A 10 mH inductor with a 1 µF capacitor resonates near 1.59 kHz.
Real Components
Real inductors have winding resistance, capacitance, core loss, saturation, and a self-resonant frequency. Real capacitors have ESR, ESL, leakage, tolerance, and voltage dependence.
Use component impedance curves and self-resonant-frequency data when frequency or accuracy matters.