State the working principle of dynamo?

Working: 1. when armature rotates with its axis perpendicular to magnetic field , the magnetic flux linking to the coil changes and an emf is induced in the coil. Therefore an induced current flows in the coil and in the external circuit connected to the coil through brushes and the slip rings. 2, The plane of coil rotates such that the arm AD goes down the plane of paper, and the arm BC becomes above the plane of paper. 3. Using Fleming's Right hand rule, we find that the current flows in the direction of CBAD and in the outer circle from Brush B2 To B1. 4. After half a rotation, the arm Bc goes down and the arm AD goes above.Using Fleming's Right hand rule, the current flows in the direction DABC and in outer circuit from brush B1 to B2. 5. Thus during half a rotation of coil, current flows in one direction and next half of rotation , current flows in the opposite direction. This process repeats and AC current flows in the external circuit.