frequency and period

A vintage oscilloscope showing a sine wave with reversing charges, beside the title How Electronics Work, Part 6, How Alternating Current (AC) Works
How Alternating Current (AC) Works: Mastering Fundamental Electronics Part 06
DIY Electronics
Learn how alternating current works: what alternates, how to read a sine wave, frequency, period, phase, and why a 120V RMS supply peaks near 170V.