What does impedance measure in an AC circuit?

Impedance in an AC circuit measures total opposition to current flow. It encompasses not only the resistance, which is the opposition to current from resistive elements, but also includes reactance, which arises from inductive and capacitive components in the circuit.

Reactance can either store energy temporarily (as in inductors) or release energy back into the circuit (as in capacitors). Therefore, impedance combines both these effects, presenting a comprehensive measurement of how the circuit restricts the flow of alternating current.

This is essential in AC circuits, as the behavior of the current and voltage is influenced not just by the resistance but also by how these reactive components affect phase relationships and the overall behavior of the circuit. Understanding impedance allows for appropriate designs and calculations in AC system applications, such as power distribution, signal processing, and various electronic devices.