In electrical circuits, reactance is the opposition presented to alternating current by inductance and capacitance. It is measured in ohms. Along with resistance, it is one of two elements of impedance; however, while both elements involve transfer of electrical energy, no dissipation of electrical energy as heat occurs in reactance; instead, the reactance stores energy until a quarter-cycle later when the energy is returned to the circuit. Greater reactance gives smaller current for the same applied voltage.
Reactance is used to compute amplitude and phase changes of sinusoidal alternating current going through a circuit element. Like resistance, reactance is measured in ohms, with positive values indicating inductive reactance and negative indicating capacitive reactance. It is denoted by the symbol . An ideal resistor has zero reactance, whereas ideal reactors have no shunt conductance and no series resistance. As frequency increases, inductive reactance increases and capacitive reactance decreases.
