Definition
The total opposition that an alternating-current (AC) circuit offers to the flow of current. Impedance is measured in ohms and is the combined effect of resistance (from resistors) and reactance (from inductors and capacitors). Unlike simple resistance in a DC circuit, impedance changes with the frequency of the AC signal.
Plain English
How much an AC circuit pushes back against the flow of electricity. It is like resistance, but it also includes the extra opposition that coils and capacitors add when the current is constantly changing direction.
Context Anchor
Seen in aircraft electrical systems, avionics, antennas, microphones, headsets, and radio wiring discussions.
Derivation
From the Latin 'impedire,' meaning 'to hinder' or 'to entangle' (literally 'to shackle the feet'). The word captures the idea of something that gets in the way of flow — in this case, the flow of alternating current.
Why Pilots Care
Correct impedance matching is required for efficient radio transmission and reception; mismatch reduces signal strength and can damage equipment.
Analogy
Think of trying to push water through a hose that partly resists the flow. Impedance is like the total “pushback” the electrical signal feels as it moves through the circuit.
Intuition Check
Impedance is not just ordinary resistance. Resistance is part of it, but impedance also includes effects that matter when the electrical signal is changing back and forth.
Example Sentence 1
The technician checked that the antenna's impedance matched the transceiver's output to ensure full transmission strength.
Example Sentence 2
High impedance in the wiring caused weak signals on the navigation radios during the flight.