Red Seal Electrician Practice
MotorsQuestion 1213 of 1506

What causes ripple torque, also called cogging, in a permanent magnet motor?

  1. Arcing between the brushes and the commutator bars of the armature
  2. Magnetic pull between the rotor magnet poles and the stator pole pieces
  3. Eddy currents in the shaft bearings and end bells
  4. A low supply voltage at the motor terminals
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Correct answer: Magnetic pull between the rotor magnet poles and the stator pole pieces

The permanent rotor magnet is pulled toward the stator iron when it passes near it, even with no coil current.

Source: Lessons in Electric Circuits II: AC (Kuphaldt), 13.2: Synchronous Motors

Practice motors

Questions last reviewed: 18 October 2026