What does reactance refer to in AC circuits?

Reactance refers to the opposition that an inductor or capacitor presents to alternating current (AC) due to their inherent properties. In AC circuits, unlike direct current (DC), the current and voltage can change direction periodically. Reactance arises from two components: inductive reactance, which occurs in inductors due to the magnetic fields they create as current flows through them, and capacitive reactance, which arises in capacitors due to their ability to store and release electrical energy.

Inductive reactance increases with frequency, as it is directly proportional to the frequency of the AC signal, while capacitive reactance decreases with frequency, being inversely proportional to it. This behavior gives reactance a significant role in determining how AC circuits respond to various frequencies.

Understanding reactance is critical for designing circuits using inductors and capacitors, as it impacts the circuit's overall impedance, a measure that combines resistance and reactance. Thus, the definition of reactance captures its essential role in AC circuit behavior, highlighting how it differs fundamentally from resistance, which is a measure of opposition to current in all types of circuits.