NEIEP Mechanics Practice Exam

What process allows an elementary DC generator to convert AC into DC?

1. Induction

2. Rectification

3. Commutation

4. Transformation

The correct answer is: Commutation

In the context of an elementary DC generator, the correct process that allows the conversion of alternating current (AC) into direct current (DC) is commutation. Commutation involves the switching of the current direction in the windings of the generator. As the armature rotates within the magnetic field, the coils of wire experience changing magnetic flux, inducing an alternating current. To convert this AC into DC, the commutator—typically a split-ring device—ensures that the current flowing to the external circuit is in one direction. This is achieved by making contact with different segments of the armature winding, effectively correcting the output current to be unidirectional. It’s worth noting that while rectification could refer to processes that convert AC to DC, in the context of a DC generator specifically, the term more aptly describes processes involving external components like diodes, which are not intrinsic to the operation of the generator itself. Induction refers to the generation of current through magnetic fields and is part of the fundamental operation of generators but does not directly describe the conversion process of AC to DC. Transformation usually refers to the manipulation of voltage levels in AC systems via transformers and does not apply to the DC generation process directly.