The hertz (symbol: Hz) is the SI unit of frequency. Its base unit is s-1 (also called inverse seconds, or 1/s). In English, hertz is used as both singular and plural.

One hertz simply means "one cycle per second"; 100 Hz means "one hundred cycles per second", and so on. The unit may be applied to any periodic event – for example, a clock might be said to tick at 1 Hz, or a human heart might be said to beat at 1.2 Hz. The frequency of aperiodic events, such as radioactive decay, are expressed in becquerels.

## History

The hertz is named after the German physicist Heinrich Rudolf Hertz, who made important scientific contributions to electromagnetism. The name was established by the IEC in 1930 [1]. It was adopted by the CGPM (Conférence générale des poids et mesures) in 1960, replacing the previous name for the unit, cycles per second (cps), along with its related multiples, primarily kilocycles (kc) and megacycles (Mc). The term cycles per second was largely replaced by hertz by the 1970's.

## SI multiples

Multiple Name Symbol Multiple Name Symbol
100 hertz Hz
101 decahertz daHz 10–1 decihertz dHz
102 hectohertz hHz 10–2 centihertz cHz
103 kilohertz kHz 10–3 millihertz mHz
106 megahertz MHz 10–6 microhertz µHz
109 gigahertz GHz 10–9 nanohertz nHz
1012 terahertz THz 10–12 picohertz pHz
1015 petahertz PHz 10–15 femtohertz fHz
1018 exahertz EHz 10–18 attohertz aHz
1021 zettahertz ZHz 10–21 zeptohertz zHz
1024 yottahertz YHz 10–24 yoctohertz yHz

## Applications

Sound is a travelling wave which is an oscillation of pressure. Humans perceive frequency of sound waves as pitch. Each musical note corresponds to a particular frequency which can be scientifically measured in hertz. Although the human ear is able to perceive frequencies ranging from 16 Hz to 20,000 Hz, the average human can hear sounds between 20 Hz and 16,000 Hz.