Reactive Reactive

Reactive - Definition and Overview

This article is about electronics. For a disscussion of "reactive" or "reactance" in chemistry, see reactivity.

Internal link 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

If X = 0, then the circuit is purely resistive, i.e. it has no reactance.

If X < 0, it is said to be capacitive. The reciprocal of reactance is susceptance.

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

<math>Z = R + j X \,<math>

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

<math>\left | Z \right | = \sqrt {R^2 + X^2} \,<math>

where

Z is impedance, measured in ohms

R is resistance, measured in ohms

X is reactance, measured in ohms 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

<math>X_L=2\pi fL \,\!<math>

where

XL is the inductive reactance, measured in ohms

f is the frequency, measured in hertz

L is the inductance, measured in henry

Capacitive reactance (symbol XC) reflects the fact that electrons can not pass through a capacitor, 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

<math>X_C= \frac {1} {2\pi fC} \,<math>

where

XC is the capacitive reactance measured in ohms

f is the frequency, measured in hertz

C is the capacitance, measured in farad

SI electricity units

SI electromagnetism units

edit  (http://www.wordiq.com/definition/Template:SI_electromagnetism_units)

Name Symbol Dimensions Quantity
ampere (SI base unit) A A Current
coulomb C A·s Electric charge, Quantity of electricity
volt V J/C = kg·m2·s−3·A−1 Potential difference
ohm Ω V/A = kg·m2·s−3·A−2 Resistance, Impedance, Reactance
ohm metre Ω·m kg·m3·s−3·A−2 Resistivity
farad F C/V = kg−1·m−2·A2·s4 Capacitance
farad per metre F/m kg−1·m−3·A2·s4 Permittivity
reciprocal farad F−1 kg1·m2·A−2·s−4 Elastance
siemens S Ω−1 = kg−1·m−2·s3·A2 Conductance, Admittance, Susceptance
siemens per metre S/m kg−1·m−3·s3·A2 Conductivity
weber Wb V·s = kg·m2·s−2·A−1 Magnetic flux
tesla T Wb/m2 = kg·s−2·A−1 Magnetic flux density
ampere per metre A/m m−1·A magnetic induction
ampere-turns per weber A/Wb kg−1·m−2·s2·A2 Reluctance
henry H V·s/A = kg·m2·s−2·A−2 Inductance
henry per metre H/m kg·m·s−2·A−2 Permeability
(dimensionless) - - Magnetic susceptibility


External links

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