D.C. Motor

• When the circuit is closed, current flows in the direction ABCDA
• Using Fleming's left-hand rule, AB will experience a downward force, and CD will experience a upward force. This pair of forces makes the coil rotate anticlockwise untilit reaches a vertical position.
• At this point, current is cut off, but momentum of coil will carry it beyond the vertical position where the split-ring Y will touch P and split-ring X will touch Q.
• The direction of the current coil reverses each time the coil passes the vertical position.
• Purpose of split-ring commutator XY is to reverse the direction of the current in the coil every half a revolution to ensure that the coil will always turn in the same direction.