The left-hand rule of magnetic polarity is a method of either determining the direction of charged particles after they enter a magnetic field or the way a simple motor works. The left-hand rule is also known as Fleming's left-hand rule, after John Fleming, the electronics innovator who created the rule.
In regard to magnetic polarity, the left-hand rule shows the direction of the magnetic force, electrical current and magnetic field when a charged particle comes into contact with a magnetic field. It is performed by contorting the left hand in such a way so that the index finger points in the direction of the magnetic field. The middle finger should, in a 90-degree angle, point towards the electrical current. The thumb then forms a 90-degree angle with the index finger and points in the direction of the force being applied on the particle.
Fleming's left-hand rule can also be used to help diagram a simple motor. As a conductor passes through a magnetic field, the opposite fields repel each other to cause motion. When using the left-hand rule to explain a motor, the hand position stays the same. The index finger points toward the direction of the magnetic field, the middle finger toward the current and the thumb towards the direction the current moves.