Working principle of Self-starter: It is based on the principle of Fleming’s Left Hand Rule, which states that when the thumb, fore finger and middle finger of the left hand are position at right angle to each other as shown in the figure then, fore finger indicates the direction of the magnetic field, the middle finger represents the direction of the current in the conductor and the thumb indicates the direction of the force on the conductor.
When a current carrying conductor is placed in a magnetic field, a mechanical force is experienced by the conductor. The magnitude of this force (F) is directly proportional to the magnetic field strength (B) and the current (I) flowing in the conductor.