The correct answer is: A. stator supply is relieved of responsibility of producing magnetic field.
A synchronous motor is a type of AC motor that has a rotating magnetic field produced by a DC current in the rotor. The stator windings are connected to an AC power source, and the rotor windings are connected to a DC power source. The stator windings produce a rotating magnetic field, which induces a current in the rotor windings. The current in the rotor windings creates a magnetic field that interacts with the stator magnetic field, causing the rotor to rotate.
The power factor of a motor is the ratio of the real power (the power that is used to do work) to the apparent power (the product of the voltage and current). The power factor of a synchronous motor is typically higher than the power factor of an induction motor. This is because the stator windings of a synchronous motor do not have to produce the magnetic field. The magnetic field is produced by the rotor windings, which are connected to a DC power source. This means that the stator windings of a synchronous motor only have to carry the current that is required to produce the torque to turn the rotor. The stator windings of an induction motor, on the other hand, have to carry both the current that is required to produce the torque to turn the rotor and the current that is required to produce the magnetic field. This means that the stator windings of an induction motor have to carry more current than the stator windings of a synchronous motor. The higher current in the stator windings of an induction motor causes the power factor of an induction motor to be lower than the power factor of a synchronous motor.
Options B, C, and D are incorrect because they do not explain why the power factor of a synchronous motor is better than that of an induction motor.