### Definition of Impedance

1. Noun. A material's opposition to the flow of electric current; measured in ohms.

Exact synonyms: Electric Resistance, Electrical Resistance, Ohmic Resistance, Resistance, Resistivity
Generic synonyms: Electrical Phenomenon
Specialized synonyms: Ohmage
Derivative terms: Resistive

### Definition of Impedance

1. n. 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 current. It is equal to R2 + X2, where R = ohmic resistance, X = reactance. For an inductive circuit, X = 2πfL, where f = frequency and L = self-inductance; for a circuit with capacity X = 1 ÷ 2πfC, where C = capacity.

### Definition of Impedance

1. Noun. (physics) A measure of the opposition to the flow of an alternating current in a circuit; the aggregation of its resistance, inductive and capacitive reactance. Represented by the symbol Z. ¹

2. Noun. (physics usually with “mechanical”) a measure of opposition to motion of something subjected to a force. ¹

3. Noun. (physics usually with “acoustic” or “sound”) the sound pressure divided by the particle velocity and the surface area through which an acoustic wave propagates. ¹

4. Noun. (context: by analogy software engineering usually with “mismatch”) a measure of the opposition caused by differences between two paradigms, especially between object-oriented development and relational databases ¹

¹ Source: wiktionary.com

1. [n -S]

### Medical Definition of Impedance

1. 1. Total opposition to flow. When flow is steady, impedance is simply the resistance, e.g., the driving pressure per unit flow; when flow is changing, impedance also includes the factors that oppose changes in flow. Thus, deviations of impedance, from simple ohmic resistance because of the effects of capacitance and inductance, become more important in alternating current as the frequency of oscillations increases. In fluid analogies (e.g., pulsatile flow of blood, to-and-fro flow of respiratory gas), impedance depends not only on viscous resistance but also upon compressibility, compliance, inertance, and the frequency of imposed oscillations. 2. Resistance of an acoustic system to being set in motion. (05 Mar 2000)

### Lexicographical Neighbors of Impedance

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### Literary usage of Impedance

Below you will find example usage of this term as found in modern and/or classical literature:

1. Transactions of the American Institute of Electrical Engineers by American Institute of Electrical Engineers (1917)
"The mutual impedance, for alternating currents, between a pair of terminals and ... 917 Self impedance. The self impedance between a pair of terminals of a ..."

2. Alternating-current Electricity and Its Applications to Industry by William Henry Timbie, Henry Harold Higbie (1916)
"and 5.0 per cent impedance while the 9.6:1 transformer has 1 per cent resistance ... Effect of Unequal Percentages of impedance in Parallel Transformers. ..."

3. Alternating-current Electricity and Its Applications to Industry: Second Course by William Henry Timbie, Henry Harold Higbie (1916)
"Effect of Unequal Percentages of impedance in Parallel Transformers. ... This means that the total internal drop due to equivalent impedance must be the ..."

4. Report of the Annual Meeting (1899)
"CONSTRUCTION OP AN impedance CHART. 7. ... The Complete impedance Curve. — The actual impedance is due to both effects, ..."

5. Electrical Phenomena in Parallel Conductors by Frederick Eugene Pernot (1918)
"The expression for this impedance is set up in the same manner as for ... The load-end impedance is the ratio between the load voltage and the load current. ..."

6. Electrical Phenomena in Parallel Conductors by Frederick Eugene Pernot (1918)
"General Expression for Generator-end impedance.— The complex ratio between the generator voltage and the generator current, when these two quantities are ..."

7. A Course in Electrical Engineering by Chester Laurens Dawes (1922)
"A non-inductive resistance and an impedance coil are connected in series across 120-volt 60-cycle mains. The voltage across the resistance is found to be 90 ..."

8. Electrical Papers by Oliver Heaviside (1894)
"impedance FORMULAE FOR SHORT LINES. RESISTANCE OF TUBES. In the case of a short line, a very high frequency is needed in general to make it necessary to ..."