Impedance and Reactance

$Z = R + jX \qquad V = IZ$

Element	Impedance	Phase
Resistor	$R$	V and I in phase
Inductor	$jX_L = j\omega L$	current lags by 90°
Capacitor	$-jX_C = \dfrac{1}{j\omega C}$	current leads by 90°

Memory aid: ELI the ICE man — in an inductor (L), voltage E leads current I; in a capacitor (C), current I leads voltage E.

$|Z| = \sqrt{R^2 + X^2}$ and $\theta = \tan^{-1}(X/R)$. Admittance is $Y = 1/Z = G + jB$.