Red Seal Electrician Practice
Power factor and three-phaseQuestion 1264 of 1506

A large induction motor runs with no load. The power factor is very low. Why?

  1. The rotor is shorted, so the current in the stator is all resistive.
  2. The slip is at its maximum value when there is no load.
  3. Almost no resistance reflects from the rotor, so the load is reactive.
  4. The stator field has stopped rotating at no load.
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Correct answer: Almost no resistance reflects from the rotor, so the load is reactive.

With no load the rotor reflects almost no resistance to the stator, so the motor looks like a transformer with an open secondary.

Source: Lessons in Electric Circuits II: AC (Kuphaldt), 13.7: Tesla Polyphase Induction Motors

Practice power factor and three-phase

Questions last reviewed: 18 October 2026