An electrical motor consists of a rectangular coil ABCD of insulated copper wire. The coil is placed between the two poles of a magnetic field such that the arm AB and CD are perpendicular to the direction of the magnetic field. The ends of the coil are connected to the two halves P and Q of a split ring. The inner sides of these halves are insulated and attached to an axle. P and Q touch two stationary conducting brushes X and Y respectively.
Current in the coil ABCD enters from the source battery through conducting brush X and flows back to the battery through brush Y. Current in the arm AB flows from A to B an in the arm CD flows from C to D. On applying Fleming’s Left Hand rule the force acting on the arm AB pushes it downwards while the force acting on arm CD pushes upwards. Thus the coil and the axle O rotate anti-clockwise. After half rotation, Q makes contact with the brush X and P with brush Y. Therefore the current in the coil gets reversed and flows along DCBA. The split rings act as a commutator. The reversing of the current is repeated at each half rotation, giving rise to a continuous rotation of the coil and to the axle.