Definition
The negative electrode in an electron tube whose surface is coated with a mixture of metal oxides — typically barium and strontium oxides — that release electrons readily when heated. The coating allows the cathode to emit a strong stream of electrons at a relatively low operating temperature.
Plain English
A part inside an electron tube that gives off electrons when it gets hot. A special coating on its surface lets it do this without needing to be as hot as a plain metal cathode would.
Context Anchor
Seen in aircraft electrical and radio maintenance discussions, especially when studying older vacuum-tube equipment.
Derivation
Cathode comes from the Greek 'kathodos,' meaning 'a way down' — referring to the path electrons travel from this electrode. 'Coated' simply describes the oxide layer added to its surface to improve electron emission.
Why Pilots Care
Most modern aircraft use solid-state electronics, but older aircraft equipment may still refer to vacuum-tube parts. Knowing this term helps a pilot or mechanic understand maintenance descriptions for older radios or electronic systems.
Intuition Check
Do not think of the coating as just a protective paint. In a coated cathode, the coating is part of how the cathode works: it helps electrons leave the surface more easily.
Example Sentence 1
The radio's coated cathode warmed up for a few seconds before the set produced sound.
Example Sentence 2
Older aircraft communication equipment used vacuum tubes whose coated cathodes required careful warm-up before full operation.