Generator and alternator are two devices, which converts
mechanical energy into electrical energy. Both have the same
principle of electromagnetic induction, the only difference is
that their construction. Generator persists stationary magnetic
field and rotating conductor which rolls on the armature with
slip rings and brushes riding against each other, hence it
converts the induced emf into dc current for external load
whereas an alternator has a stationary armature and rotating
magnetic field for high voltages but for low voltage output
rotating armature and stationary magnetic field is used.