Because the armature windings are formed in loops or coils, current flows outward in one direction and returns in the opposite direction. This means the magnetic lines of force are oriented in opposite directions in each of the two segments of the loop. When placed in the stationary magnetic field of the field coils, one part of the armature coil is pushed in one direction while the other part is pushed in the opposite direction. This causes the coil, and the shaft to which it is mounted, to rotate. Each end of the armature windings is connected to one segment of the commutator. Two carbon brushes are connected to one terminal of the power supply. The brushes contact the commutator segments, conducting current to and from the armature coils.
As the armature coil turns through a half revolution, the contact of the brushes on the commutator causes the current flow to reverse in the coil. The commutator segment attached to each coil end will have traveled past one brush and is now in contact with the other. In this way, current flow is maintained constantly in one direction while allowing the segment of the rotating armature coils to reverse polarity as they rotate. This ensures that the armature will turn in one direction.