Definition
A memory aid used to determine the direction of force on a current-carrying conductor placed in a magnetic field. Using the left hand, the thumb, index finger, and middle finger are held at right angles to each other. The index finger points in the direction of the magnetic field (north to south), the middle finger points in the direction of current flow (from negative to positive, the electron-flow convention), and the thumb then points in the direction the conductor will be pushed. This predicted force is what causes the rotor of an electric motor to turn.
Plain English
A simple hand trick that tells you which way an electric motor will spin. Hold out your left hand with thumb, first finger, and second finger all at right angles. Point your first finger along the magnetic field and your second finger along the current, and your thumb shows which way the wire gets pushed.
Context Anchor
Seen when studying aircraft electrical systems, starter motors, and basic motor operation in maintenance or ground school material.
Derivation
Called the left-hand rule because it is performed with the left hand, distinguishing it from the right-hand rule used for generators. The left hand is used here because it matches the electron-flow convention (negative to positive) that was standard in early electrical engineering texts.
Why Pilots Care
Pilots do not apply this rule in the cockpit, but it underpins how every electric motor on the aircraft works -- starters, fuel pumps, trim motors, gyros. Understanding it makes electrical system behavior and troubleshooting easier to follow.
Grounding Statement
Picture a wire sitting between magnet poles; when electric current flows through the wire, the magnetic field pushes the wire, and that push is what makes a motor turn.
Intuition Check
This is not a rule about turning left or flying a left-hand traffic pattern. It is a memory aid for predicting the direction of push inside an electric motor.
Example Sentence 1
The instructor used the left-hand rule for electric motors to show why reversing the current makes the starter motor spin the opposite direction.
Example Sentence 2
During system checks, the technician applied the left-hand rule for electric motors to verify actuator movement matched the wiring diagram.