Impedance Summary

Impedance is the combination of Resistance (\(R\)) and Reactance (\(X\)).

Resistance is the real part of impedance; when a circuit is driven with DC, there is no distinction between impedance and resistance.

Reactance is the imaginary part of impedance. A capacitor has purely reactive impedance that is inversely proportional to signal frequency. \(X_C = \frac{-1}{2\pi f C}\). Inductive reactance is proportional to signal frequency \(f \) and the inductance \(L\). \(X_L = 2 \pi f L\).

The total reactance is given by \(X = X_L + X_C\). Note \(X_C\) is negative.

The total impedance is \(Z = R + jX\)