The rotor of a permanent magnet motor turns at the same speed as the stator's magnetic field.

• A. False
• B. Not enough information
• C. True
• D. Always

Answer: (C)

In a permanent-magnet motor, the stator creates a rotating magnetic field. The rotor, which has permanent magnets, is pulled in step with that field and tends to rotate at the same angular speed as the field. In steady operation there is no slip between rotor and field, so the rotor speed equals the synchronous speed set by the supply frequency and the motor’s pole count (synchronous speed = 120 f / P). If conditions push the machine toward losing synchronism, that would be a special case, but under normal operation a permanent-magnet motor runs with the rotor turning at the same speed as the stator’s magnetic field.