What does frequency measure, and in what unit is it expressed?

Frequency measures how many cycles of a wave occur per second, and it is expressed in hertz (Hz). One hertz equals one cycle per second; a kilohertz (kHz) is a thousand cycles per second, and a megahertz (MHz) is a million. Frequency is important for AC power (60 Hz in North America) and for radio, where different stations broadcast at different frequencies. Higher frequency means more cycles per second and shorter wavelengths. Distinguishing frequency (Hz) from voltage (volts), resistance (ohms), and charge (coulombs) is common on the Electronics subtest.