While DC generators work on the same general principle of electromagnetic induction, their
construction is not as simple as their AC counterparts. With a DC generator, the coil of wire is
mounted in the shaft where the magnet is on the AC alternator, and electrical connections are
made to this spinning coil via stationary carbon rushes" contacting copper strips on the rotating
shaft. All this is necessary to switch the coil's changing output polarity to the external circuit so
the external circuit sees a constant polarity: