When current flows through a conductor, magnetic field is produced around it. The direction of this field (B) depends upon the direction of flow of electric current (I). Similarly when an electrical conductor is placed in a magnetic field, a force acts upon it.
The direction of this force always perpendicular to both direction of current and direction of magnetic field and the direction of the flow of current are both perpendicular to the direction of the magnetic field. If the current flowing through the conductor is increased then the force also increases. This force acting on a current conducting wire was discovered by the great scientist Michael Faraday. This principle is used in electric motors.
The direction of force acting on a current carrying conductor placed in a magnetic field can be found according to the Flemings left hand rule.
According to Fleming left hand rule, the direction of force applied to a current carrying wire is perpendicular to both the direction of the current as well as the magnetic field.
It means that, stretch the thumb, the first finger and the middle finger in such a manner that they are perpendicular to each other i.e. the angle between the pairs of fingers is 90°. Then. if the first finger shows the direction of the magnetic field and the middle one the direction of current flow, then the thumb shows the direction of force F acting on the current carrying conductor.
This rule was originated by John Ambrose Fleming in the late 19th century as a simple way of workout the direction in an electric motor or the direction of electric current in an electric generator.