At what speed does a synchronous motor operate?

A synchronous motor operates at a speed that is synchronized with the frequency of the AC power supply. This means that the speed of the motor is directly related to the frequency of the alternating current (AC) that powers it. The synchronous speed can be calculated using the formula:

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

This relationship ensures that the rotor of the motor rotates at the same speed as the magnetic field generated by the stator, which is essential for the motor to operate effectively and efficiently.

The implication of this is significant because, unlike induction motors, synchronous motors do not vary their speed under load conditions; they will maintain the synchronous speed dictated by the power supply frequency. This characteristic makes synchronous motors particularly useful in applications requiring precise speed control.

In contrast, the other options suggest variations in speed or incorrect relationships to frequency that do not apply to synchronous motors, reinforcing why the identified answer accurately encapsulates the operational principle of these machines.