reactance

In alternating current circuits containing inductors and capacitors, the factor which determines the phase relationship between current and voltage; symbol X, units ? (ohms). It is the imaginary part of impedance, controlling the power input to the circuit.

In the analysis of an alternating-current electrical circuit (for example a RLC series circuit), reactance is the imaginary part of impedance, and is caused by the presence of inductors or capacitors in the circuit.

The relationship between impedance, resistance, and reactance is given by the equation

where

Z is impedance in ohms, R is resistance in ohms, X is reactance in ohms, and j is the imaginary unit .

Often it is enough to know the magnitude of the impedance:

For a purely inductive or capacitive element, the magnitude of the impedance simplifies to just the reactance.

The reactance is given by

where XL and XC are the inductive and capacitive reactances, respectively.

Inductive reactance has the formula

where

XL is the inductive reactance, measured in ohms ω is the angular frequency, measured in radians per second f is the frequency, measured in hertz L is the inductance, measured in henries

Capacitive reactance (symbol XC) reflects the fact that electrons cannot pass through a capacitor, yet effectively alternating current (AC) can: the higher the frequency the better.

Capacitive reactance has the formula

where

XC is the capacitive reactance measured in ohms ω is the angular frequency, measured in radians per second f is the frequency, measured in hertz C is the capacitance, measured in farads