# Impedance

﻿
Impedance

Impedance is a concept associated with the transmission of waves and electrical signals. There are many kinds of waves, and impedance is different in each of them, hence this disambiguation page. However, impedance is also a unifying concept. It is related to the load that is imposed on the source that generates a wave. It governs the reflection and transmission of waves incident on a change of medium. If the impedances in the two media match, there will be no reflection. One simple approach identifies two parameters for a wave: the restoring force that tries to return to equilibrium and the inertia of the medium displaced. Then the impedance is

Z = the square root of (restoring force) times (inertia)

while the velocity of the wave is

v = the square root of (restoring force) divided by (inertia)

For example, for a sound wave the restoring force is the modulus of elasticity, while the inertia is just the density. For some waves (light waves, for example) it is not obvious how this simple picture for mechanical waves can be applied, but the same general picture holds.

Impedance may refer to:

*the ratio of the voltage phasor to the electric current phasor, as in
**Electrical impedance, a measure of opposition to time-varying electric current in an electric circuit.
**Characteristic impedance, a measure of opposition to electric current propagation in a transmission line.
*Impedance matching and Impedance mismatch.
*Vacuum impedance, a universal constant.
*Electromagnetic impedance, a constant related to electromagnetic wave propagation in a medium.
*Mechanical impedance, a measure of opposition to motion of a structure subjected to a force.
*Acoustic impedance, a constant related to the propagation of sound waves in an acoustic medium.
*Linear response function, a general way to represent the input-output characteristics of a system.
*Object-relational impedance mismatch, difficulties encountered when a relational database management system is in an object-oriented programming language.

Wikimedia Foundation. 2010.

### Look at other dictionaries:

• impédance — [ ɛ̃pedɑ̃s ] n. f. • 1892; angl. impedance (1886); du lat. impedire « empêcher » ♦ Électron. Rapport (exprimé en ohms) entre les valeurs efficaces de la tension aux bornes d un circuit et de l intensité du courant sinusoïdal qui le traverse. L… …   Encyclopédie Universelle

• Impedance — Impédance Cette page d’homonymie répertorie les différents sujets et articles partageant un même nom. Le terme Impédance est utilisé dans plusieurs domaines: Celui de l électricité et de l électronique, voir l article Impédance (électricité)… …   Wikipédia en Français

• Impedance — Im*ped ance, n. [Impede + ance.] (Elec.) The apparent resistance in an electric circuit to the flow of an alternating current, analogous to the actual electrical resistance to a direct current, being the ratio of electromotive force to the… …   The Collaborative International Dictionary of English

• impedance — index deterrent, offset Burton s Legal Thesaurus. William C. Burton. 2006 …   Law dictionary

• impedance — (n.) 1886, from IMPEDE (Cf. impede) + ANCE (Cf. ance) …   Etymology dictionary

• impedance — ► NOUN ▪ the effective resistance to an alternating electric current arising from the combined effects of ohmic resistance and reactance …   English terms dictionary

• impedance — [im pēd′ ns] n. [< IMPED(E) + ANCE] 1. the total opposition offered by an electric circuit to the flow of an alternating current of a single frequency: it is a combination of resistance and reactance and is measured in ohms: the reciprocal of… …   English World dictionary

• Impédance — Cette page d’homonymie répertorie les différents sujets et articles partageant un même nom. Le terme Impédance est utilisé dans plusieurs domaines: Celui de l électricité et de l électronique, voir l article Impédance (électricité) Impédance… …   Wikipédia en Français

• impedance — kompleksinės varžos modulis statusas T sritis Standartizacija ir metrologija apibrėžtis Apibrėžtį žr. priede. priedas( ai) Grafinis formatas atitikmenys: angl. impedance; modulus of impedance vok. Betrag der Impedanz, m; impedanz Modul, m rus.… …   Penkiakalbis aiškinamasis metrologijos terminų žodynas

• impédance — kompleksinės varžos modulis statusas T sritis Standartizacija ir metrologija apibrėžtis Apibrėžtį žr. priede. priedas( ai) Grafinis formatas atitikmenys: angl. impedance; modulus of impedance vok. Betrag der Impedanz, m; impedanz Modul, m rus.… …   Penkiakalbis aiškinamasis metrologijos terminų žodynas

### Share the article and excerpts

##### Direct link
Do a right-click on the link above
and select “Copy Link”

We are using cookies for the best presentation of our site. Continuing to use this site, you agree with this.