Definition
A length of wire wound into loops, used to either generate a magnetic field when current flows through it, or to produce an electrical voltage when exposed to a changing magnetic field. In aircraft instruments, coils are core components used to sense magnetism, drive needles, or transfer signals.
Plain English
A piece of wire wrapped around in circles. When electricity moves through it, it acts like a small magnet. When a magnetic field moves around it, it produces electricity. That two-way relationship is what makes coils useful in instruments.
Context Anchor
Seen in the flux gate compass system, where coils in the remote compass sensor help turn Earth’s magnetic field into heading information for the cockpit display.
Derivation
From the Old French 'coillir,' meaning 'to gather' or 'to collect.' A coil is wire 'gathered' into loops. The shape matters: winding wire into loops concentrates and strengthens the magnetic effect, which is why coils — not straight wires — are used.
Why Pilots Care
Coils are the working element in many instruments and electrical components a pilot relies on, including the flux gate compass and magnetos. Knowing what a coil does makes it easier to understand how these systems sense or generate the signals that drive cockpit indications.
Analogy
Think of wrapping a garden hose into a neat circle instead of laying it straight. The shape matters. With wire, winding it into loops makes its magnetic effect much stronger than a straight piece of wire.
Intuition Check
Do not think of an electrical coil as just a spring-shaped piece of metal. In aviation instruments, it is usually wound wire used to create or sense magnetic effects.
Example Sentence 1
In the flux gate compass, small electrical coils sense the direction of the Earth's magnetic field and pass that information to the heading indicator.
Example Sentence 2
As the aircraft turns, the changing magnetic flux through each electrical coil produces signals that the system converts into an accurate heading indication.