Hertz measures phenomena like sound waves (hearing, music) and electromagnet waves (radio, light). When waves pass from medium to medium, such as from a musical instrument to an ear, their wavelength changes, but the frequency remains virtually the same.

## Identifying Herz

Hertz (Hz) measures frequency, or how often an episode cycles within a certain timeframe. Finding the frequency means first choosing the unit of time (second, minute or hour), and then counting the cycles within that timeframe. Hertz frequency equals 1 cycle/sec, so hertz only cycles once per second.

## Range of Frequency

Electrical and audio signals pick up wide ranges of hertz, with prefixes like kilo and mega, giga and tera. A kilohertz equals 1,000 HZ, a gigahertz is equivalent to 1 million Hz, and 1 quadrillion Hz add up to 1 petrahertz. Frequencies less than 1 Hz use decimals--1 kilohertz 10-3 equals .001, and 1 gigahertz 10-9 is equivalent to .000000001.

## Significance

In music, the pitch tone "A" above middle "C" has a frequency of 440 Hz, while the other "A" notes cycle at 55 and 110 Hz on the low end all the way up to 3520 and 7040 Hz on the high end. Infants hear a greater range of frequencies than adults, up to about 20,000 Hz.