Principles and Working of DC machines

  The rotor contains the commutator and the conductors across which emf is induced. This part is called armature.

  The stator has two poles one labeled N and the other S. The field windings are situated on the poles.
  The rotor consists of an iron core that has slots which house the armature conductors and a commutator and the brushes.
  The figure shows the connections of the coils to the commutator
  A uniform magnetic field is produced in the small air gaps between the poles and the rotor when current is passed through the field windings. This induces an emf across the coil and looks like as shown below.

  When the armature windings are connected to the commutator according to the connections shown earlier , the individual emf gets rectified and all of them add up together.