Definition
A coil of insulated wire wound around an iron pole shoe inside a generator or motor that produces the magnetic field when current flows through it. The strength of this magnetic field controls the output voltage of a generator or the torque of a motor.
Plain English
A coil of wire inside a generator or motor that becomes a magnet when electricity passes through it. That magnetism is what lets the device produce electricity or turn a shaft.
Context Anchor
Seen in aircraft electrical system discussions, especially when learning how generators, alternators, motors, and relays work.
Derivation
From 'field' meaning the magnetic field surrounding the coil, and 'coil' meaning the wound loops of wire. The wire is wound into a coil specifically to concentrate and shape the magnetic field it creates.
Why Pilots Care
A failed field coil stops the generator from charging the battery, leading to electrical failure in flight.
Analogy
A field coil is like wrapping wire around a nail to make a simple electromagnet: when current flows, the wrapped wire creates magnetism.
Intuition Check
Do not read field as an open area of land here. In this term, field means a magnetic effect created around the coil.
Example Sentence 1
When the voltage regulator detects low system voltage, it increases current to the field coil, which strengthens the magnetic field and raises the generator's output.
Example Sentence 2
A broken field coil prevented the generator from producing any output.