What is produced when DC power is applied to the rotor of a synchronous motor?

When DC power is applied to the rotor of a synchronous motor, it generates a magnetic field with distinct north and south poles. This occurs because the DC current flowing through the rotor windings creates an electromagnet. The generated magnetic field is essential for the operation of the synchronous motor, as it interacts with the rotating magnetic field produced by the stator.

As the rotor’s magnetic field rotates, it aligns with the stator's magnetic field, leading the rotor to synchronize with the rotating field. This synchronization is critical for the motor to operate efficiently at constant speed, dictated by the supply frequency. The presence of the distinct north and south poles allows the motor to produce torque, enabling it to perform work.

In contrast, the other options—voltage drop, magnetic resistance, and induced current—do not directly occur simply as a result of applying DC power to the rotor. While they may involve concepts relevant to electrical motors in broader contexts, they do not specifically address the immediate effect of DC current on the rotor of a synchronous motor.