Hertz
hertz | |
---|---|
SI | |
Unit of | frequency |
Symbol | Hz |
Named after | Heinrich Hertz |
In SI base units | s−1 |
The hertz (symbol: Hz) is the unit of
Some of the unit's most common uses are in the description of
Definition
The hertz is equivalent to one
In English, "hertz" is also used as the plural form.[5] 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 event per second" (where the event being counted may be a complete cycle); 100 Hz means "one hundred events 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
Even though frequency,
- and
The hertz is named after
History
The hertz is named after the German physicist Heinrich Hertz (1857–1894), who made important scientific contributions to the study of electromagnetism. The name was established by the International Electrotechnical Commission (IEC) in 1935.[8] It was adopted by the General Conference on Weights and Measures (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 per second" (kc/s) and "megacycles per second" (Mc/s), and occasionally "kilomegacycles per second" (kMc/s). The term "cycles per second" was largely replaced by "hertz" by the 1970s.[9][failed verification]
In some usage, the "per second" was omitted, so that "megacycles" (Mc) was used as an abbreviation of "megacycles per second" (that is, megahertz (MHz)).[10]
Applications
Sound and vibration
Electromagnetic radiation
Electromagnetic radiation is often described by its frequency—the number of oscillations of the perpendicular electric and magnetic fields per second—expressed in hertz.
Radio frequency radiation is usually measured in kilohertz (kHz), megahertz (MHz), or gigahertz (GHz). Light is electromagnetic radiation that is even higher in frequency, and has frequencies in the range of tens (infrared) to thousands (ultraviolet) of terahertz. Electromagnetic radiation with frequencies in the low terahertz range (intermediate between those of the highest normally usable radio frequencies and long-wave infrared light) is often called terahertz radiation. Even higher frequencies exist, such as that of gamma rays, which can be measured in exahertz (EHz). (For historical reasons, the frequencies of light and higher frequency electromagnetic radiation are more commonly specified in terms of their wavelengths or photon energies: for a more detailed treatment of this and the above frequency ranges, see Electromagnetic spectrum.)
Computers
In computers, most
Various computer buses, such as the front-side bus connecting the CPU and northbridge, also operate at various frequencies in the megahertz range.
SI multiples
Submultiples | Multiples | ||||
---|---|---|---|---|---|
Value | SI symbol | Name | Value | SI symbol | Name |
10−1 Hz | dHz | decihertz | 101 Hz | daHz | decahertz |
10−2 Hz | cHz | centihertz | 102 Hz | hHz | hectohertz |
10−3 Hz | mHz | millihertz | 103 Hz | kHz | kilohertz |
10−6 Hz | μHz | microhertz | 106 Hz | MHz | megahertz |
10−9 Hz | nHz | nanohertz | 109 Hz | GHz | gigahertz |
10−12 Hz | pHz | picohertz | 1012 Hz | THz | terahertz |
10−15 Hz | fHz | femtohertz | 1015 Hz | PHz | petahertz |
10−18 Hz | aHz | attohertz | 1018 Hz | EHz | exahertz |
10−21 Hz | zHz | zeptohertz | 1021 Hz | ZHz | zettahertz |
10−24 Hz | yHz | yoctohertz | 1024 Hz | YHz | yottahertz |
10−27 Hz | rHz | rontohertz | 1027 Hz | RHz | ronnahertz |
10−30 Hz | qHz | quectohertz | 1030 Hz | QHz | quettahertz |
Common prefixed units are in bold face. |
Higher frequencies than the International System of Units provides prefixes for are believed to occur naturally in the frequencies of the quantum-mechanical vibrations of massive particles, although these are not directly observable and must be inferred through other phenomena. By convention, these are typically not expressed in hertz, but in terms of the equivalent energy, which is proportional to the frequency by the factor of the Planck constant.
Unicode
The CJK Compatibility block in Unicode contains characters for common SI units for frequency. These are intended for compatibility with East Asian character encodings, and not for use in new documents (which would be expected to use Latin letters, e.g. "MHz").[15]
- U+3390 ㎐ SQUARE HZ (Hz)
- U+3391 ㎑ SQUARE KHZ (kHz)
- U+3392 ㎒ SQUARE MHZ (MHz)
- U+3393 ㎓ SQUARE GHZ (GHz)
- U+3394 ㎔ SQUARE THZ (THz)
See also
- Alternating current
- Bandwidth (signal processing)
- Electronic tuner
- FLOPS
- Frequency changer
- Normalized frequency (signal processing)
- Orders of magnitude (frequency)
- Orders of magnitude (rotational speed)
- Periodic function
- Radian per second
- Rate
- Sampling rate
Notes
- ^ Although hertz is equivalent to cycle per second (cps), the SI explicitly states that "cycle" and "cps" are not units in the SI, likely due to ambiguity in the terms.[2]
- ^ "(d) The hertz is used only for periodic phenomena, and the becquerel (Bq) is used only for stochastic processes in activity referred to a radionuclide."[6]
- Atomic vibrationsare typically on the order of tens of terahertz
References
- ^ "hertz". (1992). American Heritage Dictionary of the English Language (3rd ed.), Boston: Houghton Mifflin.
- ^ a b "SI Brochure: The International System of Units (SI) – 9th edition" (PDF). BIPM: 26. Retrieved 7 August 2022.
- ^ "SI Brochure: The International System of Units (SI) § 2.3.1 Base units" (PDF) (in British English and French) (9th ed.). BIPM. 2019. p. 130. Retrieved 2 February 2021.
- ^ "SI Brochure: The International System of Units (SI) § Appendix 1. Decisions of the CGPM and the CIPM" (PDF) (in British English and French) (9th ed.). BIPM. 2019. p. 169. Retrieved 2 February 2021.
- ^ NIST Guide to SI Units – 9 Rules and Style Conventions for Spelling Unit Names, National Institute of Standards and Technology
- BIPM. Retrieved 24 October 2012.
- ^ "SI brochure, Section 2.2.2, paragraph 6". Archived from the original on 1 October 2009.
- ^ "IEC History". Iec.ch. Archived from the original on 19 May 2013. Retrieved 6 January 2021.
- ^ Cartwright, Rufus (March 1967). Beason, Robert G. (ed.). "Will Success Spoil Heinrich Hertz?" (PDF). Electronics Illustrated. Fawcett Publications, Inc. pp. 98–99.
- hdl:1721.1/5042.
- ^ Ernst Terhardt (20 February 2000). "Dominant spectral region". Mmk.e-technik.tu-muenchen.de. Archived from the original on 26 April 2012. Retrieved 28 April 2012.
- ^ "Black Hole Sound Waves – Science Mission Directorate". science.nasa.go.
- ^ "Black Hole Sound Waves – Science Mission Directorate". science.nasa.go.
- ^ Asaravala, Amit (30 March 2004). "Good Riddance, Gigahertz". Wired. Retrieved 28 April 2012.
- ^ Unicode Consortium (2019). "The Unicode Standard 12.0 – CJK Compatibility ❰ Range: 3300—33FF ❱" (PDF). Unicode.org. Retrieved 24 May 2019.
External links
- SI Brochure: Unit of time (second)
- National Research Council of Canada: Cesium fountain clock
- National Research Council of Canada: Optical frequency standard based on a single trapped ion (archived 23 December 2013)
- National Research Council of Canada: Optical frequency comb (archived 27 June 2013)
- National Physical Laboratory: Time and frequency Optical atomic clocks