In which single-phase motor, the rotor has no teeth or winding ?

Split phase motor
Reluctance motor
Hysteresis motor
Universal motor

The correct answer is: B. Reluctance motor

A reluctance motor is a type of single-phase AC motor that has no rotor windings. Instead, the rotor is made of a ferromagnetic material that is magnetized by the stator field. The rotor turns because of the difference in magnetic reluctance between the stator and rotor poles.

A split-phase motor is a type of single-phase AC motor that has two windings on the stator. The main winding is connected directly to the power supply, and the auxiliary winding is connected to the power supply through a capacitor. The capacitor creates a phase shift between the currents in the two windings, which causes the motor to start.

A hysteresis motor is a type of single-phase AC motor that has a rotor made of a ferromagnetic material with high hysteresis loss. The rotor is magnetized by the stator field, and the rotor turns because of the hysteresis loss in the rotor material.

A universal motor is a type of single-phase AC motor that can be operated on either AC or DC power. The rotor of a universal motor is made of a copper winding that is short-circuited. The rotor turns because of the interaction between the stator field and the rotor current.

In conclusion, the correct answer is: B. Reluctance motor. A reluctance motor is a type of single-phase AC motor that has no rotor windings. Instead, the rotor is made of a ferromagnetic material that is magnetized by the stator field. The rotor turns because of the difference in magnetic reluctance between the stator and rotor poles.