Fleming's left-hand rule
Fleming's left-hand rule is used to find the direction of the force on a conductor in a magnetic field when a current is sent through it.
Fleming's left-hand rule
Hold the thumb, first finger and middle finger of the left hand at right angles to one another. Point the middle finger in the direction of the current and the first finger in the direction of the magnetic field; the thumb then points in the direction of the force on the conductor.
Figure to be added
| Finger | Points along | A way to remember |
|---|---|---|
| First finger | the Field | First — Field |
| Middle finger | the Current | seCond finger — Current |
| Thumb | the force, so the Motion | thuMb — Motion |
Why a left hand
Three directions at right angles — field, current, force — can be arranged in two mirror-image ways, and only one of them matches nature. The left hand happens to give the right one. Check it on activity 13.3: field from N to S across the gap, current along BC, and the thumb points the way the wire rolled. Reverse the current (turn the hand so the middle finger points the other way) and the thumb reverses, just as the wire did. Later in the chapter a right-hand rule will appear for a different job, finding an induced current, so keep the two hands apart: left for motors, right for generators.
Current means conventional current
The middle finger points along the conventional current, from + to −, not along the flow of electrons.
Left hand for the force
First finger — field, middle finger — current, thumb — force (motion).