The speed of a single-phase AC motor can be controlled by changing which factors?

The correct choice is founded on the fundamental principles of how single-phase AC motors operate. The speed of these motors is primarily determined by the frequency of the electrical supply and the number of poles in the motor design.

When the frequency of the AC supply is altered, it directly impacts the synchronous speed of the motor. Synchronous speed is calculated using the formula:

[ \text{Synchronous Speed (RPM)} = \frac{120 \times \text{Frequency (Hz)}}{\text{Number of Poles}} ]

This indicates that increasing the frequency will increase the speed of the motor, while decreasing the frequency will lower the speed.

The number of poles also plays a crucial role. A motor can be designed with a different number of poles, and this affects how quickly the magnetic field rotates, thereby influencing the motor's speed. Reducing the number of poles raises the speed at which the motor operates, while increasing the number of poles reduces the speed.

Therefore, by manipulating either the frequency of the electrical input or the number of poles within the motor, one can effectively control the speed of a single-phase AC motor. The other factors—such as voltage—do not have the same direct influence on speed and primarily affect torque and efficiency rather