impedance

impedance — noun

1. the combined force that slows or blocks the flow of electricity in a circuit tha

1.nounC2
Definition

the combined force that slows or blocks the flow of electricity in a circuit that carries changing current (alternating current). It includes the effects of resistance, capacitance, and inductance, and is measured in a unit called the ohm.

Example

Élise measured the impedance of the new speakers to see if they matched the amplifier.

measure + impedance + of [component]

The cable had a high impedance, so the signal grew weak before reaching Daichi's recorder.

high impedance causes signal loss

Common collocations
  • high impedance
  • low impedance
  • input impedance
  • output impedance
  • characteristic impedance
  • total impedance
  • measure impedance
  • calculate impedance
  • match impedance
Synonyms
  • resistance

    Related but distinct — resistance applies to DC circuits and is only one part of impedance; impedance includes both resistance and reactance for AC circuits.

  • reactance

    The component of impedance that comes from capacitance and inductance, not from pure resistance.

Antonyms
  • conductance

    The measure of how easily electricity flows through a circuit — the opposite of impedance.

Grammar Patterns

the impedance of [device/circuit]

[adjective] impedance

impedance + verb

Usage Note

Impedance is the AC (alternating current) equivalent of resistance in DC (direct current) circuits. The symbol is Z, and the unit is the ohm (Ω). Commonly used in speaker specifications, audio equipment, and circuit design. Input impedance and output impedance are two frequently encountered types.

Common Mistakes

The impedance of this DC battery is five ohms.
The resistance of this DC battery is five ohms.
Impedance is a term for alternating current (AC); for direct current (DC), the correct term is resistance.
This wire has zero impedance.
This wire has very low impedance.
All real circuits have some impedance; zero impedance only exists in theoretical ideal models.

Word family

  • impede
    verbC1
  • impediment
    nounC1
  • impeded
    adjectiveC1

Synonym discussion

Sense: noun/1

In electrical contexts, impedance, resistance, and reactance are closely related but distinct. Resistance (symbol R) is the opposition to the flow of direct current (DC) and is a real number measured in ohms. Reactance (symbol X) is the opposition caused by capacitors and inductors in an alternating current (AC) circuit, and it varies with frequency. Impedance (symbol Z) combines both resistance and reactance into a single value that describes the total opposition to AC flow. Think of resistance as the friction in a pipe, reactance as the springy walls that push back when the flow changes direction, and impedance as the combined effect of both. For example, a speaker rated at 8 ohms impedance may have 6 ohms of resistance and 2 ohms of reactance at certain frequencies.

resistance ↗reactanceimpedance ↗

Common collocations

Nouns

Phrases

  • input impedance
  • output impedance
  • high impedance
  • low impedance
  • characteristic impedance

Prepositions

Etymology

LatinFrenchEnglish

Impedance comes from the Latin verb 'impedire,' meaning 'to shackle' or 'to hinder.' This verb was formed from 'in-' (in, on) and 'pes/pedis' (foot) — literally 'to put a shackle on the foot,' which slows a person down. The English verb 'impede' (to slow or block) appeared in the early 1600s, and by the late 1800s, engineers working with the newly understood physics of electricity borrowed the concept to describe anything that 'hinders' the flow of electric current. The suffix '-ance' turns the verb into a noun meaning 'the state or quality of' impeding.