The correct answer is D. All of the above.
A DC generator is a device that converts mechanical energy into electrical energy by using the principle of electromagnetic induction. The generator has a rotating armature that is surrounded by a stator. The armature is made up of a number of coils of wire that are wound around a core. The stator is made up of a number of permanent magnets. When the armature rotates, it cuts through the magnetic field of the stator, which induces an electric current in the coils of the armature. The current is then collected by brushes and slip rings and is sent to an external load.
The efficiency of a DC generator is the ratio of the electrical power output to the mechanical power input. The efficiency of a DC generator is affected by a number of factors, including the load, the speed, and the voltage. The efficiency of a DC generator is usually highest at full load, rated speed, and rated voltage.
Here is a brief explanation of each option:
- Full load: The efficiency of a DC generator is usually highest at full load. This is because the generator is designed to operate at its maximum efficiency at full load.
- Rated r.p.m.: The efficiency of a DC generator is also affected by the speed. The efficiency of a DC generator is usually highest at its rated speed.
- Rated voltage: The efficiency of a DC generator is also affected by the voltage. The efficiency of a DC generator is usually highest at its rated voltage.