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
1886; impede + -ance; term introduced by O. Heaviside
Related forms
self-impedance, noun
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

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
Word Origin and History for impedance
n.

1886, from impede + -ance.

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.
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.
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)