# Hertz

Hertz
Unit systemSI derived unit
Unit ofFrequency
SymbolHz
Named afterHeinrich Hertz
In SI base unitss−1
Top to bottom: Lights flashing at frequencies f = 0.5 Hz, 1.0 Hz and 2.0 Hz, i.e. at 0.5, 1.0 and 2.0 flashes per second, respectively. The time between each flash – the period T – is given by ​1f (the reciprocal of f ), i.e. 2, 1 and 0.5 seconds, respectively.

The hertz (symbol: Hz) is the derived unit of frequency in the International System of Units (SI) and is defined as one cycle per second.[1] It is named for Heinrich Rudolf Hertz, the first person to provide conclusive proof of the existence of electromagnetic waves. Hertz are commonly expressed in multiples: kilohertz (103 Hz, kHz), megahertz (106 Hz, MHz), gigahertz (109 Hz, GHz), terahertz (1012 Hz, THz), petahertz (1015 Hz, PHz), and exahertz (1018 Hz, EHz).

Some of the unit's most common uses are in the description of sine waves and musical tones, particularly those used in radio- and audio-related applications. It is also used to describe the speeds at which computers and other electronics are driven.

## Definition

The hertz is defined as one cycle per second. The International Committee for Weights and Measures defined the second as "the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom"[2][3] and then adds: "It follows that the hyperfine splitting in the ground state of the caesium 133 atom is exactly 9 192 631 770 hertz, ν(hfs Cs) = 9 192 631 770 Hz." The dimension of the unit hertz is 1/time (1/T). Expressed in base SI units it is 1/second (1/s).

In English, "hertz" is also used as the plural form.[4] As an SI unit, Hz can be prefixed; commonly used multiples are kHz (kilohertz, 103 Hz), MHz (megahertz, 106 Hz), GHz (gigahertz, 109 Hz) and THz (terahertz, 1012 Hz). One hertz simply means "one cycle per second" (typically that which is being counted is a complete cycle); 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 occurrence rate of aperiodic or stochastic events is expressed in reciprocal second or inverse second (1/s or s−1) in general or, in the specific case of radioactive decay, in becquerels.[5] Whereas 1 Hz is 1 cycle per second, 1 Bq is 1 aperiodic radionuclide event per second.

Even though angular velocity, angular frequency and the unit hertz all have the dimension 1/s, angular velocity and angular frequency are not expressed in hertz,[6] but rather in an appropriate angular unit such as radians per second. Thus a disc rotating at 60 revolutions per minute (rpm) is said to be rotating at either 2π rad/s or 1 Hz, where the former measures the angular velocity and the latter reflects the number of complete revolutions per second. The conversion between a frequency f measured in hertz and an angular velocity ω measured in radians per second is

${\displaystyle \omega =2\pi f\,}$ and ${\displaystyle f={\frac {\omega }{2\pi }}\,}$.

This SI unit is named after Heinrich Hertz. As with every International System of Units (SI) unit named for a person, the first letter of its symbol is upper case (Hz). However, when an SI unit is spelled out in English, it is treated as a common noun and should always begin with a lower case letter (hertz)—except in a situation where any word in that position would be capitalized, such as at the beginning of a sentence or in material using title case.

Other Languages
Afrikaans: Hertz
العربية: هرتز
asturianu: Herciu
azərbaycanca: Hers
বাংলা: হার্জ
Bân-lâm-gú: Hertz
беларуская (тарашкевіца)‎: Гэрц (адзінка вымярэньня)
български: Херц
བོད་ཡིག: ཧེར་ཚི།
bosanski: Herc
brezhoneg: Hertz
català: Hertz
čeština: Hertz
Cymraeg: Hertz
dansk: Hertz
eesti: Herts
Ελληνικά: Χερτζ
español: Hercio
Esperanto: Herco
euskara: Hertz
فارسی: هرتز
français: Hertz
Gaeilge: Heirts
galego: Hertz

한국어: 헤르츠
हिन्दी: हर्ट्ज़
hrvatski: Herc
Bahasa Indonesia: Hertz
interlingua: Hertz
íslenska: Herts
italiano: Hertz
עברית: הרץ
Basa Jawa: Hertz
қазақша: Герц
Kiswahili: Hezi
Кыргызча: Герц
Latina: Hertz
latviešu: Hercs
Lëtzebuergesch: Hertz (Eenheet)
lietuvių: Hercas
magyar: Hertz
македонски: Херц
मराठी: हर्ट्‌झ
Bahasa Melayu: Hertz
монгол: Герц (нэгж)
Nederlands: Hertz (eenheid)

Nordfriisk: Hertz
norsk: Hertz
norsk nynorsk: Hertz
occitan: Hertz
олык марий: Герц (шотлымаш)
پنجابی: ہرٹز
Piemontèis: Hertz
polski: Herc
português: Hertz
română: Hertz
русиньскый: Гертз
Scots: Hertz
shqip: Herci
sicilianu: Hertz
Simple English: Hertz
slovenčina: Hertz (jednotka)
slovenščina: Herc
српски / srpski: Херц
srpskohrvatski / српскохрватски: Herc
Basa Sunda: Hertz
suomi: Hertsi
svenska: Hertz
தமிழ்: ஏர்ட்சு
తెలుగు: హెర్ట్జ్
тоҷикӣ: Ҳертс
Türkçe: Hertz
українська: Герц
اردو: ہرٹز
Tiếng Việt: Hertz
Winaray: Hertz