What happens to the speed of the rotating magnetic field as the number of poles in a stator increases?

When discussing the relationship between the speed of the rotating magnetic field and the number of poles in a stator, it's essential to understand how the synchronous speed is calculated. The synchronous speed of a motor is determined by the formula:

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

This equation shows that synchronous speed is inversely proportional to the number of poles. As the number of poles increases, while the frequency remains constant, the synchronous speed decreases. More poles mean that the same electrical frequency must create more magnetic fields within the motor, which slows down the rotation of the magnetic field.

Consequently, when the number of poles in a stator increases, the speed of the rotating magnetic field decreases, confirming that the correct answer is that the speed decreases. This characteristic is fundamental to the operation of electric machines and exploration of their design and performance characteristics.