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Hertz

The hertz (symbol: Hz) is the unit of frequency in the International System of Units (SI), equivalent to one event (or cycle) per second.[1][3] The hertz is an SI derived unit whose expression in terms of SI base units is s−1, meaning that one hertz is the reciprocal of one second.[2] It is named after Heinrich Rudolf Hertz (1857–1894), the first person to provide conclusive proof of the existence of electromagnetic waves. Hertz are commonly expressed in multiples: kilohertz (kHz), megahertz (MHz), gigahertz (GHz), terahertz (THz).

hertz
Top to bottom: Lights flashing at frequencies f = 0.5 Hz, 1.0 Hz and 2.0 Hz; that is, 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 ); that is, 2, 1 and 0.5 seconds, respectively.
General information
Unit systemSI
Unit offrequency
SymbolHz
Named afterHeinrich Hertz
In SI base unitss−1

Some of the unit's most common uses are in the description of periodic waveforms and musical tones, particularly those used in radio- and audio-related applications. It is also used to describe the clock speeds at which computers and other electronics are driven. The units are sometimes also used as a representation of the energy of a photon, via the Planck relation E = , where E is the photon's energy, ν is its frequency, and h is the Planck constant.

Definition

The hertz is equivalent to one cycle per second. The International Committee for Weights and Measures defined the second as "the duration of 9192631770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom"[4][5] and then adds: "It follows that the hyperfine splitting in the ground state of the caesium 133 atom is exactly 9192631770 hertz, νhfs Cs = 9192631770 Hz." The dimension of the unit hertz is 1/time (T−1). Expressed in base SI units, the unit is the reciprocal second (1/s).

In English, "hertz" is also used as the plural form.[6] 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 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 radioactivity, in becquerels.[7] Whereas 1 Hz is one cycle (or periodic event) per second, 1 Bq is one radionuclide event per second on average.

Even though frequency, angular velocity, angular frequency and radioactivity all have the dimension T−1, of these only frequency is expressed using the unit hertz.[8] Thus a disc rotating at 60 revolutions per minute (rpm) is said to have an angular velocity of 2π rad/s and a frequency of rotation of 1 Hz. The correspondence between a frequency f with the unit hertz and an angular velocity ω with the unit radians per second is

  and  

The hertz is named after Heinrich Hertz. As with every SI unit named for a person, its symbol starts with an upper case letter (Hz), but when written in full it follows the rules for capitalisation of a common noun; i.e., "hertz" becomes capitalised at the beginning of a sentence and in titles, but is otherwise in lower case.

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.[9] 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.[10][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)).[11]

Applications

 
A sine wave with varying frequency
 
A heartbeat is an example of a non-sinusoidal periodic phenomenon that may be analyzed in terms of frequency. Two cycles are illustrated.

Sound and vibration

Sound is a traveling longitudinal wave, which is an oscillation of pressure. Humans perceive the frequency of a sound as its pitch. Each musical note corresponds to a particular frequency. An infant's ear is able to perceive frequencies ranging from 20 Hz to 20000 Hz; the average adult human can hear sounds between 20 Hz and 16000 Hz.[12] The range of ultrasound, infrasound and other physical vibrations such as molecular and atomic vibrations extends from a few femtohertz[13] into the terahertz range[14] and beyond.[15]

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 central processing units (CPU) are labeled in terms of their clock rate expressed in megahertz (MHz) or gigahertz (GHz). This specification refers to the frequency of the CPU's master clock signal. This signal is nominally a square wave, which is an electrical voltage that switches between low and high logic levels at regular intervals. As the hertz has become the primary unit of measurement accepted by the general populace to determine the performance of a CPU, many experts have criticized this approach, which they claim is an easily manipulable benchmark. Some processors use multiple clock cycles to perform a single operation, while others can perform multiple operations in a single cycle.[16] For personal computers, CPU clock speeds have ranged from approximately 1 MHz in the late 1970s (Atari, Commodore, Apple computers) to up to 6 GHz in IBM Power microprocessors.

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

SI multiples of hertz (Hz)
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").[17]

  • U+3390 SQUARE HZ
  • U+3391 SQUARE KHZ
  • U+3392 SQUARE MHZ
  • U+3393 SQUARE GHZ
  • U+3394 SQUARE THZ

See also

Notes and references

  1. ^ "hertz". (1992). American Heritage Dictionary of the English Language (3rd ed.), Boston: Houghton Mifflin.
  2. ^ a b "SI Brochure: The International System of Units (SI) – 9th edition" (PDF). BIPM: 26. Retrieved 7 August 2022.
  3. ^ 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]
  4. ^ "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.
  5. ^ "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.
  6. ^ NIST Guide to SI Units – 9 Rules and Style Conventions for Spelling Unit Names, National Institute of Standards and Technology
  7. ^ "(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." "BIPM – Table 3". BIPM. Retrieved 24 October 2012.
  8. ^ . Archived from the original on 1 October 2009.
  9. ^ . Iec.ch. Archived from the original on 19 May 2013. Retrieved 6 January 2021.
  10. ^ Cartwright, Rufus (March 1967). Beason, Robert G. (ed.). "Will Success Spoil Heinrich Hertz?" (PDF). Electronics Illustrated. Fawcett Publications, Inc. pp. 98–99.
  11. ^ Pellam, J. R.; Galt, J. K. (1946). "Ultrasonic Propagation in Liquids: I. Application of Pulse Technique to Velocity and Absorption Measurements at 15 Megacycles". The Journal of Chemical Physics. 14 (10): 608–614. Bibcode:1946JChPh..14..608P. doi:10.1063/1.1724072. hdl:1721.1/5042.
  12. ^ Ernst Terhardt (20 February 2000). . Mmk.e-technik.tu-muenchen.de. Archived from the original on 26 April 2012. Retrieved 28 April 2012.
  13. ^ "Black Hole Sound Waves – Science Mission Directorate". science.nasa.go.
  14. ^ Atomic vibrations are typically on the order of tens of terahertz
  15. ^ "Black Hole Sound Waves – Science Mission Directorate". science.nasa.go.
  16. ^ Asaravala, Amit (30 March 2004). "Good Riddance, Gigahertz". Wired. Retrieved 28 April 2012.
  17. ^ 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
  • (archived 23 December 2013)
  • (archived 27 June 2013)
  • National Physical Laboratory: Time and frequency Optical atomic clocks
  • Online Tone Generator

hertz, this, article, about, unit, measure, rental, company, corporation, other, uses, disambiguation, megahertz, redirect, here, other, uses, disambiguation, megahertz, disambiguation, hertz, symbol, unit, frequency, international, system, units, equivalent, . This article is about the unit measure For the car rental company see The Hertz Corporation For other uses see Hertz disambiguation Hz and Megahertz redirect here For other uses see Hz disambiguation and Megahertz disambiguation The hertz symbol Hz is the unit of frequency in the International System of Units SI equivalent to one event or cycle per second 1 3 The hertz is an SI derived unit whose expression in terms of SI base units is s 1 meaning that one hertz is the reciprocal of one second 2 It is named after Heinrich Rudolf Hertz 1857 1894 the first person to provide conclusive proof of the existence of electromagnetic waves Hertz are commonly expressed in multiples kilohertz kHz megahertz MHz gigahertz GHz terahertz THz hertzTop to bottom Lights flashing at frequencies f 0 5 Hz 1 0 Hz and 2 0 Hz that is at 0 5 1 0 and 2 0 flashes per second respectively The time between each flash the period T is given by 1 f the reciprocal of f that is 2 1 and 0 5 seconds respectively General informationUnit systemSIUnit offrequencySymbolHzNamed afterHeinrich HertzIn SI base unitss 1Some of the unit s most common uses are in the description of periodic waveforms and musical tones particularly those used in radio and audio related applications It is also used to describe the clock speeds at which computers and other electronics are driven The units are sometimes also used as a representation of the energy of a photon via the Planck relation E hn where E is the photon s energy n is its frequency and h is the Planck constant Contents 1 Definition 2 History 3 Applications 3 1 Sound and vibration 3 2 Electromagnetic radiation 3 3 Computers 4 SI multiples 5 Unicode 6 See also 7 Notes and references 8 External linksDefinition EditThe hertz is equivalent to one cycle per second The International Committee for Weights and Measures defined the second as the duration of 9192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom 4 5 and then adds It follows that the hyperfine splitting in the ground state of the caesium 133 atom is exactly 9192 631 770 hertz nhfs Cs 9192 631 770 Hz The dimension of the unit hertz is 1 time T 1 Expressed in base SI units the unit is the reciprocal second 1 s In English hertz is also used as the plural form 6 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 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 radioactivity in becquerels 7 Whereas 1 Hz is one cycle or periodic event per second 1 Bq is one radionuclide event per second on average Even though frequency angular velocity angular frequency and radioactivity all have the dimension T 1 of these only frequency is expressed using the unit hertz 8 Thus a disc rotating at 60 revolutions per minute rpm is said to have an angular velocity of 2p rad s and a frequency of rotation of 1 Hz The correspondence between a frequency f with the unit hertz and an angular velocity w with the unit radians per second is w 2 p f displaystyle omega 2 pi f and f w 2 p displaystyle f frac omega 2 pi The hertz is named after Heinrich Hertz As with every SI unit named for a person its symbol starts with an upper case letter Hz but when written in full it follows the rules for capitalisation of a common noun i e hertz becomes capitalised at the beginning of a sentence and in titles but is otherwise in lower case History EditFurther information Cycle per second 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 9 It was adopted by the General Conference on Weights and Measures CGPM Conference generale 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 10 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 11 Applications Edit A sine wave with varying frequency A heartbeat is an example of a non sinusoidal periodic phenomenon that may be analyzed in terms of frequency Two cycles are illustrated Sound and vibration Edit Sound is a traveling longitudinal wave which is an oscillation of pressure Humans perceive the frequency of a sound as its pitch Each musical note corresponds to a particular frequency An infant s ear is able to perceive frequencies ranging from 20 Hz to 20000 Hz the average adult human can hear sounds between 20 Hz and 16000 Hz 12 The range of ultrasound infrasound and other physical vibrations such as molecular and atomic vibrations extends from a few femtohertz 13 into the terahertz range 14 and beyond 15 Electromagnetic radiation Edit 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 Edit Further information on why the frequency including for gigahertz GHz etc is a flawed speed indicator for computers Megahertz myth In computers most central processing units CPU are labeled in terms of their clock rate expressed in megahertz MHz or gigahertz GHz This specification refers to the frequency of the CPU s master clock signal This signal is nominally a square wave which is an electrical voltage that switches between low and high logic levels at regular intervals As the hertz has become the primary unit of measurement accepted by the general populace to determine the performance of a CPU many experts have criticized this approach which they claim is an easily manipulable benchmark Some processors use multiple clock cycles to perform a single operation while others can perform multiple operations in a single cycle 16 For personal computers CPU clock speeds have ranged from approximately 1 MHz in the late 1970s Atari Commodore Apple computers to up to 6 GHz in IBM Power microprocessors 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 EditSee also Orders of magnitude frequency SI multiples of hertz Hz Submultiples MultiplesValue SI symbol Name Value SI symbol Name10 1 Hz dHz decihertz 101 Hz daHz decahertz10 2 Hz cHz centihertz 102 Hz hHz hectohertz10 3 Hz mHz millihertz 103 Hz kHz kilohertz10 6 Hz µHz microhertz 106 Hz MHz megahertz10 9 Hz nHz nanohertz 109 Hz GHz gigahertz10 12 Hz pHz picohertz 1012 Hz THz terahertz10 15 Hz fHz femtohertz 1015 Hz PHz petahertz10 18 Hz aHz attohertz 1018 Hz EHz exahertz10 21 Hz zHz zeptohertz 1021 Hz ZHz zettahertz10 24 Hz yHz yoctohertz 1024 Hz YHz yottahertz10 27 Hz rHz rontohertz 1027 Hz RHz ronnahertz10 30 Hz qHz quectohertz 1030 Hz QHz quettahertzCommon 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 EditThe 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 17 U 3390 SQUARE HZ U 3391 SQUARE KHZ U 3392 SQUARE MHZ U 3393 SQUARE GHZ U 3394 SQUARE THZSee also EditAlternating current Bandwidth signal processing Electronic tuner FLOPS Frequency changer Normalized frequency signal processing Orders of magnitude frequency Periodic function Radian per second Rate Sampling rateNotes and references Edit 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 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 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 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 BIPM Table 3 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 Pellam J R Galt J K 1946 Ultrasonic Propagation in Liquids I Application of Pulse Technique to Velocity and Absorption Measurements at 15 Megacycles The Journal of Chemical Physics 14 10 608 614 Bibcode 1946JChPh 14 608P doi 10 1063 1 1724072 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 Atomic vibrations are typically on the order of tens of terahertz 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 EditSI 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 Online Tone Generator Retrieved from https en wikipedia org w index php title Hertz amp oldid 1137985290, wikipedia, wiki, book, books, library,

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