What distinguishes a synchronous motor from an induction motor?

The distinct characteristic that differentiates a synchronous motor from an induction motor is that synchronous motors operate at a speed that is precisely aligned with the rotating magnetic field produced by the stator. This means that for a synchronous motor, the rotor speed matches the synchronous speed, which is determined by the frequency of the electrical supply and the number of poles in the motor. As a result, synchronous motors maintain constant speed regardless of the load up to their rated limits.

In contrast, induction motors do not achieve synchronous speed under load; they typically operate at a slightly lower speed due to slip between the stator's rotating magnetic field and the rotor. Therefore, option C correctly identifies that synchronous motors turn at exactly the same speed as the rotating magnetic field, highlighting the essential operational principle of synchronous motors. Understanding this fundamental difference is crucial for selecting appropriate motor types for various applications based on speed and performance characteristics.