What do a.m. and p.m. stand for?


[im-peed-ns] /ɪmˈpid ns/
Electricity. the total opposition to alternating current by an electric circuit, equal to the square root of the sum of the squares of the resistance and reactance of the circuit and usually expressed in ohms. Symbol: Z.
Also called mechanical impedance. Physics. the ratio of the force on a system undergoing simple harmonic motion to the velocity of the particles in the system.
something that impedes; an obstacle or hindrance.
Origin of impedance
1886; impede + -ance; term introduced by O. Heaviside
Related forms
self-impedance, noun Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2015.
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Examples from the web for impedance
  • Even more confusing are changes in thoracic impedance, a measurement of resistance to electric current through the lung.
  • In order for the impedance matching ear to work, certain conditions had to be met.
British Dictionary definitions for impedance


a measure of the opposition to the flow of an alternating current equal to the square root of the sum of the squares of the resistance and the reactance, expressed in ohms Z
a component that offers impedance
Also called acoustic impedance. the ratio of the sound pressure in a medium to the rate of alternating flow of the medium through a specified surface due to the sound wave Za
Also called mechanical impedance. the ratio of the mechanical force, acting in the direction of motion, to the velocity of the resulting vibration Zm
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition
© William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
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Word Origin and History for impedance

1886, from impede + -ance.

Online Etymology Dictionary, © 2010 Douglas Harper
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impedance in Science
A measure of the opposition to the flow of alternating current through a circuit. Impedance is measured in ohms. The resistance of a circuit to direct current (also measured in ohms) is generally not the same as its impedance, due to the effects of capacitance and induction in and among the components of the circuit. See also impedance matching.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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impedance in Culture
impedance [(im-peed-ns)]

A measure of the apparent resistance posed by an electrical circuit to an alternating current (AC).

Note: The term impedance is most often encountered in dealing with antennas and speakers in television, stereo, and radio systems.
The American Heritage® New Dictionary of Cultural Literacy, Third Edition
Copyright © 2005 by Houghton Mifflin Company.
Published by Houghton Mifflin Company. All rights reserved.
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impedance in Technology

electronics, physics
Opposition to flow of alternating current. Impedance consists of resistance plus reactance (capacitive or inductive). Measured in Ohms.

The Free On-line Dictionary of Computing, © Denis Howe 2010
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