A DC generator works on the principle of Faraday’s law of electromagnetic induction which says whenever a conductor is moved in the magnetic field or flux, an emf is generated in the conductors and the magnitude of the induced emf is directly proportional to the rate of change of flux linkage.
The emf generated in the conductor is of alternating nature and the generator which gives out electrical energy in the form of alternating current is called a synchronous generator or alternator.
The generator, that gives out electrical energy in the form of direct current is called a dc generator. The essential difference between the alternator and dc generator is that is an alternator slip rings are used to collect the supply, while in the dc generator, the commutator is used for this purpose. This commutator converts the alternating current induced in the conductors into direct current for the external circuit.