# impedance

[im-peed-ns] /ɪmˈpid ns/
noun
1.
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.
2.
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.
3.
something that impedes; an obstacle or hindrance.
Origin of impedance
1886
1886; impede + -ance; term introduced by O. Heaviside
Related forms
self-impedance, noun
Dictionary.com Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2015.
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Examples from the Web for impedance
Historical Examples
• These conditions are satisfied by using in the impedance coil many turns of large wire and an ample iron core.

Kempster Miller
• What is the impedance if the voltage of the line is 115 volts?

Willis Eugene Tower
• The impedance coils are wound on insulating rods, which hold them near, but not touching, the ground carbon.

Kempster Miller
• The usual diagrammatic symbol for an impedance coil is shown in Fig. 106.

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• Each Morse circuit will be seen to include, serially, two 50-ohm impedance coils, and to have shunts through condensers to ground.

Kempster Miller
• These four impedance coils are wound on separate cores and do not have any inductive relation whatsoever with each other.

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• The battery supply to the operator's transmitter is through an impedance coil 9.

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• In order to further increase the impedance, the cores are made long and heavy.

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• In applying Ohm's law to an alternating current circuit, impedance must be substituted for resistance.

Willis Eugene Tower
• The impedance these windings offer to the high frequency of lightning oscillations is great.

Kempster Miller
British Dictionary definitions for impedance

## impedance

/ɪmˈpiːdəns/
noun
1.
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
2.
a component that offers impedance
3.
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
4.
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
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
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Word Origin and History for impedance
n.

1886, from impede + -ance.

Online Etymology Dictionary, © 2010 Douglas Harper
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impedance in Science
 impedance   (ĭm-pēd'ns)    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
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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
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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.
(2003-12-02)

The Free On-line Dictionary of Computing, © Denis Howe 2010 http://foldoc.org
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