Which statement is true about synchronous speed?

Which statement is true about synchronous speed?

• A. It is determined by frequency and pole count
• B. It is determined by supply voltage
• C. It is independent of frequency
• D. It equals rotor speed at no load

Answer: (A)

The speed in question is the rotating magnetic field’s speed—how fast the field turns inside the stator. That speed is set by how often the AC supply cycles (frequency) and how many poles the winding forms. The relationship is captured by n_s = 120 f / P, so higher frequency or fewer poles speeds up the field, while more poles slow it down. Voltage doesn’t determine this speed; it mainly affects torque and current. In a typical induction motor, the rotor lags behind the rotating field by a small amount (slip) to develop torque, so the rotor speed isn’t exactly the field speed, especially under load.

The speed in question is the rotating magnetic field’s speed—how fast the field turns inside the stator. That speed is set by how often the AC supply cycles (frequency) and how many poles the winding forms. The relationship is captured by n_s = 120 f / P, so higher frequency or fewer poles speeds up the field, while more poles slow it down. Voltage doesn’t determine this speed; it mainly affects torque and current. In a typical induction motor, the rotor lags behind the rotating field by a small amount (slip) to develop torque, so the rotor speed isn’t exactly the field speed, especially under load.