Which of the following affects the electromotive force developed by a DC generator?

The electromotive force (EMF) generated by a DC generator is fundamentally influenced by the strength of the stationary magnetic field. In a DC generator, the process of generating electricity relies on the interaction between the magnetic field and the conductors moving within that field. A stronger magnetic field results in more lines of magnetic force being cut by the conductors, which enhances the induced EMF according to Faraday's law of electromagnetic induction. Essentially, the greater the magnetic field strength, the higher the induced voltage will be as the conductors cut through the field lines.

While factors such as the acceleration of conductors, their diameter, and the type of conductors can also play roles in the generation process, they do not directly impact the fundamental relationship between magnetic field strength and voltage generation in the same primary way as the stationary magnetic field strength does. Therefore, the strength of the stationary field is a critical determinant of the generated electromotive force in a DC generator.