Definition
An electrical circuit made up only of components that consume, store, or release electrical energy without adding any energy of their own. Passive components include resistors, capacitors, inductors, and transformers. A passive circuit contains no active devices such as transistors, vacuum tubes, or other amplifying elements.
Plain English
A circuit built from parts that just use or hold electrical energy, but never boost it. Nothing in the circuit makes the signal stronger.
Context Anchor
Seen in aircraft electrical system descriptions, wiring diagrams, and troubleshooting discussions.
Derivation
Passive comes from the Latin passivus, meaning 'capable of being acted upon.' The components in a passive circuit are acted upon by the electrical energy passing through them rather than acting on it to amplify it.
Why Pilots Care
Knowing whether a circuit is passive or active helps when troubleshooting avionics or interpreting maintenance manuals. Passive circuits don't need their own power supply, which affects how they fail and how they are tested.
Intuition Check
Passive does not mean the circuit is unimportant or unused. Here it means the circuit does not supply its own electrical power.
Example Sentence 1
The antenna's matching network is a passive electrical circuit, so it requires no separate power source to function.
Example Sentence 2
Avionics technicians prefer passive electrical circuits in basic instrument panels because they require no additional power draw.