Red Seal Electrician Practice
MotorsQuestion 220 of 1506

A synchronous motor is loaded until its rotor lags the stator field by 90 electrical degrees. What is true at that angle?

  1. The motor is running at no load
  2. Torque falls to zero and the motor stalls
  3. The motor becomes self-starting at once
  4. Torque peaks, and more lag loses step
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Correct answer: Torque peaks, and more lag loses step

Torque rises with the lag angle and is greatest at 90 electrical degrees. Past that angle the motor falls out of step.

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

Practice motors

Questions last reviewed: 18 October 2026