Fleming’s left-hand rule enables you to use your hand to work out the direction of motion of a current-carrying wire in a magnetic field. Hold your hand as in the picture, with the first finger pointing in the direction of the magnetic field and your second finger in the direction of the electric current. Your thumb will now point in the direction of motion of the wire.
Fleming’s left-hand rule for electric motors is one of a pair of visual mnemonics, the other being Fleming’s right-hand rule (for generators). They were originated by John Ambrose Fleming, in the late 19th century, as a simple way of working out the direction of motion in an electric motor, or the direction of electric current in an electric generator.
Whenever a current carrying conductor comes under a magnetic field, there will be force acting on the conductor. The direction of this force can be found using Fleming’s Left Hand Rule (also known as ‘Fleming’s left-hand rule for motors’).
Similarly if a conductor is forcefully brought under a magnetic field, there will be an induced current in that conductor. The direction of this force can be found using Fleming’s Right Hand Rule.
In both Fleming’s left and right hand rules, there is a relation between the magnetic field, the current and force. This relation is directionally determined by Fleming’s Left Hand rule and Fleming’s Right Hand rule respectively.
These rules do not determine the magnitude but instead show the direction of any of the three parameters (magnetic field, current, force) when the direction of the other two parameters is known. Fleming’s Left-Hand rule is mainly applicable to electric motors and Fleming’s Right-Hand rule is mainly applicable to electric generators.