Red Seal Electrician Practice
MotorsQuestion 1267 of 1506

Why is the efficiency of a lightly loaded induction motor poor?

  1. Most of the current only keeps up the magnetizing flux.
  2. The slip is too high when the load on the shaft is light.
  3. The rotor frequency rises when the load is light.
  4. The supply voltage rises when the load is light.
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Correct answer: Most of the current only keeps up the magnetizing flux.

The magnetizing current is nearly fixed, so at light load it is most of the total.

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

Practice motors

Questions last reviewed: 18 October 2026