How is impedance defined in electrical circuits?

Impedance is defined as the total opposition that a circuit presents to alternating current (AC). It incorporates not just the resistive component but also the reactive components due to inductors and capacitors. This unique characteristic of impedance is crucial in AC circuits, as it affects both the magnitude and phase of the current flowing through the circuit.

In contrast, resistance is specifically the opposition to direct current (DC) and does not account for any phase shift or reactance, which is significant in AC applications. Therefore, options focused on direct current or temperature variations do not accurately capture the nuanced nature of impedance in the context of alternating current, where both resistive and reactive elements play a pivotal role in the circuit’s behavior.