What does impedance measure in AC circuits?

Impedance is fundamentally defined as the total opposition that a circuit presents to the flow of alternating current (AC). It encompasses not just resistance, which opposes current flow in both AC and direct current (DC), but also reactance, which arises from capacitors and inductors responding to changes in current.

In an AC circuit, as the current alternates, both the resistive (real) and reactive (imaginary) components of the impedance come into play. Resistance opposes current flow directly, while reactance—comprising inductive and capacitive reactance—depends on the frequency of the current and the circuit components involved.

Thus, impedance is a critical parameter that gives a comprehensive view of how the circuit behaves under AC conditions, influencing voltage, current, and phase relationships. Understanding impedance is essential for analyzing and designing effective AC circuits.