reactance

n. (Symbol X) Electricity
Opposition to the flow of alternating current caused by the inductance and capacitance in a circuit rather than by resistance.

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The imaginary part of the impedance of an alternating-current circuit.

The impedance Z of an alternating current circuit is a complex number given by Eq. (1).
1.

2.

3.
The imaginary part X is the reactance. The units of reactance, like those of impedance, are ohms. Reactance may be positive or negative. For example, the impedance of an inductor L at frequency ω is given by Eq. (2), so X is positive. The impedance of a capacitor C is given by Eq. (3), so X is negative.

The reactance of a circuit may depend on both the resistors and the inductors or capacitors in the circuit. For example, the circuit in the illustration has admittance [Eq. (4)]
4.
and impedance [Eq. (5)], so that the reactance [Eq. (6)], depends on both the capacitor C and the resistor R.
5.

6.
See also Admittance; Electrical impedance.

Circuit with a resistor and capacitor in parallel.

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Symbol "X". Opposition to current flow without the dissipation of energy. Example: The opposition provided by inductance or capacitance to AC current.

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