Definition
A voltage induced in the windings of an electric motor or coil that opposes the applied voltage driving the current. As a motor's armature spins through the magnetic field of its own field windings, that motion generates a voltage in the armature windings. This induced voltage acts in the opposite direction to the source voltage, reducing the net current flowing through the motor as it speeds up.
Plain English
When an electric motor runs, it pushes back against the electricity feeding it. The faster the motor spins, the harder it pushes back, and the less current it draws.
Context Anchor
Seen in aircraft electrical-system discussions, especially with starter motors, generators, alternators, and coils.
Derivation
"Counter" means against or opposing. "Electromotive force" is the older term for voltage -- literally the force that moves electrons. So counter-electromotive force is simply the voltage that pushes back against the voltage driving the circuit.
Why Pilots Care
It quickly reduces the heavy current draw of a starter motor once the engine begins turning, protecting the battery and starter from overload.
Analogy
A spinning electric motor can act a little like a small generator inside itself. As it turns, it creates its own voltage pushing back against the power feeding it.
Grounding Statement
When a motor is not yet turning, there is little counter-electromotive force, so current can be high; as the motor speeds up, the opposing voltage increases and current drops.
Intuition Check
This is not a mechanical force on the airplane. Here, “force” means electrical voltage, and “counter” means that voltage is opposing the original electrical action.
Example Sentence 1
When the flap motor first starts moving, current draw is high because counter-electromotive force has not yet built up to oppose the battery voltage.
Example Sentence 2
Technicians verify that counter-electromotive force develops normally to confirm proper starter and generator function.