What distinguishes DC generators from motors?

DC generators distinguish themselves from motors primarily in their operation through an external mechanical source. While motors convert electrical energy into mechanical energy, DC generators do the reverse; they convert mechanical energy into electrical energy.

In practice, this means that a DC generator requires an external force, such as a turbine or engine, to turn the armature, which generates electricity. This mechanical input is crucial for the generating process, enabling the generator to produce DC electricity based on the principles of electromagnetic induction.

In contrast, the other options reflect misunderstandings of generator principles or serve to highlight comparisons with motors rather than core functional differences. For example, while it is true that DC generators can have variable outputs depending on speed and load, this characteristic alone does not fundamentally define their operation as compared to motors. Efficiency can also vary depending on design and application, making it an unreliable distinguishing factor. Therefore, the operational dependence on an external mechanical source is what sets DC generators apart from motors.