Definition
A capacitor whose dielectric is a high vacuum sealed inside a glass or ceramic envelope between the plates. The vacuum allows very high voltages to exist between the plates without arcing, so vacuum capacitors are used in high-power, high-frequency circuits such as aircraft and ground-station radio transmitters and antenna tuning networks.
Plain English
A capacitor that uses empty space (a vacuum) instead of a solid material between its plates. The vacuum lets it handle very high voltages without sparking across, which makes it useful in powerful radio transmitter circuits.
Context Anchor
Seen in aircraft electrical, radio, and avionics maintenance material, especially when describing older or high-power radio equipment.
Derivation
Vacuum comes from the Latin vacuus, meaning 'empty.' Capacitor comes from capacitas, meaning 'capacity to hold.' Together: a charge-holding device whose insulating space is empty of air or any other material.
Why Pilots Care
Most pilots will never touch one directly, but understanding the term helps when reading avionics maintenance documentation or transmitter specifications, where vacuum capacitors appear in the high-voltage stages.
Analogy
Think of it like a sealed container that helps hold an electrical charge safely. The empty space inside helps keep the charge separated until the circuit uses it.
Intuition Check
“Vacuum” here does not mean the aircraft vacuum system that may drive instruments. Here it means an airless space sealed inside an electrical component.
Example Sentence 1
The transmitter's final amplifier stage uses a vacuum capacitor because the voltages there are too high for an ordinary air-dielectric type.
Example Sentence 2
During inspection the technician replaced the vacuum capacitor in the avionics bay.