impedance
im-PEE-dunss
/ɪmˈpiːdəns/
The total effective opposition offered by an electric circuit to alternating current (AC), combining resistance and reactance.
Includes phase shifts between current and voltage; measured in ohms.
The story behind the word. Coined by Oliver Heaviside in 1886 from 'impede' (Latin 'impedire', to shackle the feet). In electrical circuits, AC current is 'shackled' by combined inductive and capacitive forces.
Word relationships
- total opposition: A general phrase; impedance is the precise mathematical combination of resistance and reactance.
- admittance: Admittance measures how easily alternating current flows, defined as the mathematical inverse of impedance.
Commonly confused with
- resistance: Resistance is static opposition to any current; impedance is frequency-dependent opposition to alternating current.
Word family
- impede (verb): To obstruct or slow down progress or flow.
Collocations
- characteristic impedance
- impedance matching
- high impedance
- input impedance
Example sentences
- "Matching amplifier output impedance to speaker impedance ensures maximum power transfer and clear sound." Audio system setup guide
- "High transmission line impedance causes significant power losses during long-distance AC distribution." Power grid specification
Memory hook
IMPEDANCE IMPEDES alternating current feet. Total AC circuit opposition combining resistance + reactance.
When not to use
Do not use in simple direct current (DC) circuits where only resistance exists.
Fun facts
- Headphones with high impedance (over 250 ohms) require dedicated headphone amplifiers to sound loud and dynamic.
Related words
Explore more words
resistance, inductance, impede, Oscillation, acoustic, Countermeasure
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