Red Seal Electrician Practice
AC theoryQuestion 430 of 1506

On a 60 Hz supply, how often does the polarity of each line reverse?

  1. Every 1/60 of a second
  2. Every 60 seconds
  3. Every 1/30 of a second
  4. Every 1/120 of a second
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Correct answer: Every 1/120 of a second

Polarity reverses twice per cycle, so every 1/120 s at 60 Hz.

Source: Electrical Fundamentals Competency (Industry Training Authority of BC), 7.4: Three-wire Power Supply System

Practice ac theory

Questions last reviewed: 18 October 2026