UNIT 1.8 — AC BASICS

AC fundamentals: sine waves, RMS, frequency

CERT 1 · DC/AC Theory & Safety · ~10 min

Community content — not verified by a licensed electrician. Lessons and questions here are written for study practice and pinned to NEC 2023. Code editions and local amendments vary by jurisdiction. Always confirm against your adopted code book and your licensing board's published exam outline before test day.

Alternating current reverses direction periodically, tracing a sine wave. In North America the frequency is 60 Hz — sixty complete cycles per second (50 Hz across most of Europe). One cycle spans 360 electrical degrees.

The '120 V' at a receptacle is the RMS (root-mean-square) value: the effective value that delivers the same heating power as 120 V DC. The wave actually peaks higher: V_peak = V_RMS × 1.414, so a 120 V circuit peaks near 170 V, and a 240 V circuit near 340 V.

AC won the grid because transformers — which only work on alternating current — let voltage be stepped up for low-loss transmission and back down for safe use. That ties directly to the I²R lesson: high voltage, low current, small losses.

Exam focus: RMS↔peak conversions (×1.414 and ×0.707), frequency definitions, and 'why AC' concept questions.

Frequency (NA)
60 Hz
Peak
V_RMS × 1.414
RMS
V_peak × 0.707
Knowledge check

Quiz — 3 questions

1. The peak voltage of a 120 V RMS circuit is approximately:

2. 60 Hz means:

3. AC dominates power distribution primarily because:

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