Definition
The opposition to the flow of alternating current (AC) caused by inductance or capacitance in a circuit. Reactance is measured in ohms and varies with the frequency of the applied current. Inductive reactance increases with frequency; capacitive reactance decreases with frequency.
Plain English
A kind of resistance that only shows up in AC circuits. Coils and capacitors push back against changing current, and that pushback is called reactance. Like resistance, it is measured in ohms, but its value changes depending on how fast the current is alternating.
Context Anchor
Seen in aircraft electrical system, radio, antenna, alternator, and instrument circuit discussions.
Derivation
From the Latin re- meaning 'back' and agere meaning 'to act' — literally 'acting back.' This fits the concept: coils and capacitors react against changes in current rather than simply resisting it.
Why Pilots Care
Incorrect reactance in antenna or power circuits can weaken signals or damage sensitive equipment.
Analogy
Resistance is like a narrow pipe that slows water and wastes energy as friction. Reactance is more like a spring in the pipe: it pushes back when the flow changes, then gives energy back when the flow changes again.
Grounding Statement
Reactance only matters when electricity is changing; steady direct current does not create the same kind of pushback.
Intuition Check
Reactance is not just another word for resistance. Resistance uses up electrical energy as heat; reactance stores and returns energy as the current changes.
Example Sentence 1
The technician measured the reactance of the inductor to confirm the AC circuit was operating within specification.
Example Sentence 2
Higher frequency increased the inductive reactance in the wiring, requiring a different capacitor to balance the circuit.