## Encyclopedia > Capacitive reactance

Article Content

# Reactance

Redirected from Capacitive reactance

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. Reactance is denoted by the symbol X and is measured in ohms. If X > 0 the reactance is said to be inductive, and if X < 0 it is said to be capacitive. If X = 0, then the circuit is purely resistive, i.e. it has no reactance.

Inductive reactance (symbol XL) is caused by the fact that a current is accompanied by a magnetic field; therefore a varying current is accompanied by a varying magnetic field; the latter gives an electromotive force that resists the changes in current. The more the current changes, the more an inductor resists it: the reactance is proportional with the frequency (hence zero for DC). There is also a phase difference between the current and the applied voltage.

Inductive reactance has the formula

$X_L=2\pi fL$

where f is the frequency (in hertz) and L is the inductance (in henry).

Capacitive reactance (symbol XC) reflects the fact that electrons can not pass, yet effectively alternating current (AC) can: the higher the frequency the better. There is also a phase difference between the alternating current flowing through a capacitor and the potential difference across the capacitor's electrodes.

Capacitive reactance has the formula

$X_C=1/(2\pi fC)$

where f is the frequency (in hertz) and C is the capacitance (in farad).

All Wikipedia text is available under the terms of the GNU Free Documentation License

Search Encyclopedia
 Search over one million articles, find something about almost anything!

Featured Article
 Flapper ... of men did not return from the war, leaving a significant gap between the numbers of single women and men. These factors prompted many post-war women to forget abou ...