Define 'impedance' in an AC circuit.

Impedance in an AC circuit is defined as the total opposition to current flow. This opposition is not just due to resistance but also includes the effects of inductive and capacitive reactance. Resistance is the opposition faced by direct current, but in alternating current scenarios, reactance comes into play due to the changing nature of the current and voltage over time.

Impedance combines both resistance and reactance (inductive and capacitive) into a single measure, typically expressed in ohms. This makes it essential for analyzing AC circuits, as it affects how much current will flow for a given voltage, making it a critical aspect in the design and analysis of AC circuit behavior. Recognizing that impedance encompasses all forms of opposition helps in understanding how different components interact in an AC environment.