NEIEP Mechanics Practice Exam

In a generator, the electromagnetic field is primarily created by coils wound around the pole piece. These coils are part of the rotor or stator, depending on the design of the generator. When electrical current flows through these coils, it generates a magnetic field due to the principle of electromagnetism. The interaction between this magnetic field and the mechanical movement of the generator's components is what induces voltage, allowing for the generation of electricity.

While permanent magnets can also be used to create electromagnetic fields, as indicated in one of the other options, they do not involve the dynamic generation of an electromagnetic field that can be controlled by varying the input current. An external AC power supply would not be creating the electromagnetic field within the generator; rather, it would be used to power an electric motor or other devices. Lastly, the magnetic core inside the stator enhances the magnetic field's strength but does not directly create it. Therefore, the coils wound around the pole piece are the correct answer as they are fundamental in establishing the electromagnetic field essential for the generator's operation.