Definition
The opposition that a capacitor presents to the flow of alternating current (AC), measured in ohms. Capacitive reactance decreases as the frequency of the AC or the capacitance of the capacitor increases.
Plain English
How much a capacitor resists the flow of alternating electricity. The faster the current alternates, or the bigger the capacitor, the less it resists.
Context Anchor
Seen in aircraft electrical and electronic troubleshooting, especially when working with AC circuits, capacitors, filters, radios, and signal circuits.
Derivation
From 'capacitor' (a component that stores electrical charge) and 'reactance' (from Latin 'reagere' — to act back). The capacitor 'reacts back' against changes in current, which is why it opposes AC flow.
Why Pilots Care
Aircraft AC systems and avionics depend on predictable behavior of capacitors. Understanding capacitive reactance helps a technician troubleshoot AC circuits, filters, and power supplies where capacitors are used to block, pass, or smooth signals.
Analogy
Think of a flexible rubber wall in a water line. Slow changes do not pass through it well, but quick pulses can make it flex back and forth, letting the motion carry through more easily.
Intuition Check
Capacitive reactance is not the same as ordinary resistance. Resistance opposes current in a steady way; capacitive reactance depends on how fast the current is changing and on the size of the capacitor.
Example Sentence 1
At higher frequencies, the capacitive reactance of the filter capacitor drops, allowing more of the AC signal to pass through.
Example Sentence 2
Higher frequency reduced the capacitive reactance, allowing more current through the filter.