Red Seal Electrician Practice
TransformersQuestion 211 of 1506

A sliding-contact variable transformer and a series variable resistor both lower the voltage to a small load. How do they compare?

  1. Both waste exactly the same power
  2. The resistor is the more efficient one
  3. The transformer wastes far less power
  4. The transformer cannot lower the voltage
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Correct answer: The transformer wastes far less power

A variable transformer controls voltage with little wasted power. A resistor burns the extra voltage as heat.

Source: Lessons in Electric Circuits II: AC (Kuphaldt), 10.5: Winding Configurations

Practice transformers

Questions last reviewed: 18 October 2026