Red Seal Electrician Practice
AC theoryQuestion 1157 of 1506

When you work out AC power from current and resistance, which value of current must you use?

  1. Only the real part of the current
  2. The polar magnitude of the current
  3. Only the imaginary part of the current
  4. The phase angle of the current
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Correct answer: The polar magnitude of the current

Power calculations are scalar. Complex values must be reduced to magnitudes first.

Source: Lessons in Electric Circuits II: AC (Kuphaldt), 11.2: True, Reactive, and Apparent Power

Practice ac theory

Questions last reviewed: 18 October 2026