Which statement is true regarding the function of a DC generator?

The statement that a DC generator converts mechanical energy into electrical energy is accurate and reflects the fundamental operation of this type of device. A DC generator operates based on electromagnetic induction, where mechanical energy, typically from a rotating shaft driven by a prime mover such as a turbine or engine, is transformed into electrical energy. As the rotor turns within the magnetic field, it induces a direct current in the armature windings, thus fulfilling its primary function.

The other statements do not align with the operation of a DC generator. For instance, a DC generator produces direct current, not alternating current, which disqualifies the first statement. The second statement regarding the need for an inverter is also incorrect, as inverters are used to convert direct current to alternating current, not the other way around. Lastly, while the operational speed can affect performance, DC generators are not limited to operating only at a fixed speed; they can be designed to function across a range of speeds depending on the application.