21.1.1—The terms period, frequency and peak value as applied to an alternating

An alternating voltage or current varies periodically, with period T, frequency f=1/T, angular frequency ω=2πf and peak magnitude I₀ or V₀.

Read peak from the centre line to an extreme, not peak-to-peak, and distinguish the waveform’s cycle time from its angular frequency.

A 50 Hz mains waveform has T=20 ms and ω=100π rad s⁻¹.

The mean of a symmetric AC waveform can be zero while its heating effect is not zero.