Hertz
Hertz may refer to:
- Hertz, the SI unit of frequency (cycles per second)
- 2600 hertz, the frequency that AT&T formerly put as a steady signal on any long-distance telephone line that was not currently in use
- Hertz (crater), a lunar crater that lies on the far side of the Moon
- Hertz horn, a self-contained explosive device placed in water to destroy ships or submarines
- Hertz contact stress, a description of the stress within mating parts
- Hertz Foundation, an American non-profit organization that awards fellowships to Ph.D. students
- Hertz Corporation, a rent-a-car / equipmental rental company
- Hertz doctrine, a set of foreign policy guidelines first unveiled by President George W. Bush in 2002
- Franck-Hertz experiment
- Hertz Bay Hill Classic
- Heinrich-Hertz-Turm, a radio telecommunication tower and a famous landmark of Hamburg
- Heinrich Hertz Submillimeter Telescope
- Hertzian cone, a cone of force that propagates through a brittle, amorphous or cryptocrystalline solid material from a point of impact
- Fort Hertz, a remote British Military outpost in North Eastern Burma
Hertz is the surname of:
- Heinrich Rudolf Hertz (1857-1894), physicist, German radio pioneer
- Alfred Hertz (1872-1942), conductor
- Arne Hertz, a famous Swedish co-driver in motor rallying
- Eleonora Hertz Poznanski, see also Izrael Poznański
- Gustav Hertz (1887-1975), German Nobel laureate physicist (Jewish Christian)
- Carl Hellmuth Hertz, medical researcher, son of Gustav Hertz
- Henrik Hertz (born Heymann Hertz), Danish playwright, poet
- John Hertz (fan) - Hugo Awardnominee
- John D. Hertz, founder of Yellow Cab, Hertz car rental, racehorse breeder
- Dr. Rabbi Joseph H. Hertz, Hungary-born chief Rabbi of British Empire
- Rabbi Naftali Hertz Ben Ya’acov Elchanon
- Noreena Hertz, English economist
- Robert Hertz (1881-1915), French sociologist
- Wilhelm Ritter von Hertz (1835-1902), writer, Germanist
Fictional characters
- Suzanne Hertz, a character from Code Lyoko.
See also
- Herz
Source: adapted by the editor from Wikipedia, the free encyclopedia; from the article "Hertz (disambiguation)". Image Credit.
Extended Definition: Hertz
Hertz
The hertz (symbol: Hz) is the International System of Units (SI) base unit of frequency. The definition of the hertz is based upon that for the second, namely: 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.[1]
Its base unit is cycle/s or s-1 (also called inverse seconds, reciprocal seconds). In English, hertz is used as both singular and plural. As any 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 frequencies of aperiodic events, such as radioactive decay, are expressed in becquerels.
To avoid confusion, periodically varying angles are typically not expressed in hertz, but rather in an appropriate angular unit such as radians per second. A disc rotating at 60 revolutions per minute (RPM) can thus be said to be rotating at ≈6.283 rad/s or 1 Hz, where the latter reflects the number of complete revolutions per second. The conversion between a frequency f measured in Hertz and an angular frequency ω measured in radians/s are:
- ω = 2πf and
.
| This SI unit is named after Heinrich Hertz. As with all SI units whose names are derived from the proper name of a person, the first letter of its symbol is uppercase (Hz). When an SI unit is spelled out in English, it should always begin with a lowercase letter (hertz), except for at the beginning of a sentence or in capitalized material such as a title. Note that "degree Celsius" conforms to this rule because of the "d".
— Based on The International System of Units, section 5.2. |
History
The hertz is named after the German physicist Heinrich Hertz, who made important scientific contributions to electromagnetism. The name was established by the International Electrotechnical Commission (IEC) in 1930.[2] 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). The term cycles per second was largely replaced by hertz by the 1970s.
The term "gigahertz", most commonly used in computer processor speed and radio frequency (RF) applications, can be pronounced either /ˈgigaˌhɝts/, with a hard /g/ sound or /ˈʒɪgaˌhɝts/ or /ˈdʒɪgaˌhɝts/, with a soft /ʒ/ sound at the beginning of the word. The prefix "giga-" is derived directly from the Greek "γιγας" and hence the preferred pronunciation is /ˈgɪga/. Some electrical engineers use /ˈdʒɪga/, by analogy with "gigantic".
Applications
Vibration
Sound is a traveling 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 measured in hertz. An infant's 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.[3] The range of ultrasound, infrasound and other physical vibrations such as molecular vibrations extends into the megahertz range and well beyond.
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, megahertz, or gigahertz; this is why radio dials are commonly labeled with kHz, MHz, and 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. (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.)
Computing
In computing, most central processing units (CPU) are labeled in terms of their clock speed expressed in megahertz or gigahertz (109 hertz). The number of megahertz refers to the frequency of the CPU's master clock signal ("clock speed"). This signal is simply an electrical voltage which changes from low to high and back again at regular intervals. Hertz has become the primary unit of measurement used by the general populace to determine the speed of a CPU, but many experts have criticized this approach, which they claim is an easily manipulable benchmark.[4] For home-based personal computers, the CPU has ranged from approximately 1 megahertz in the late 1970s (Atari, Commodore, Apple computers) to nearly 4 GHz in the present. This can be increased even further by increasing the frequency of the CPU in the BIOS or other software.
Various computer buses, such as memory buses connecting the CPU and system random access memory (RAM), also transfer data using clock signals operating at different frequencies in the megahertz ranges (for modern products).
Order of Magnitude
| Frequency (Hz) | Name | Unit | Frequency (Hz) | Name | Unit | |
|---|---|---|---|---|---|---|
| 100 | Hertz | Hz | ||||
| 101 | Dekahertz | daHz | 10–1 | Decihertz | dHz | |
| 102 | Hektohertz | 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 | Yoktohertz | yHz |
Frequencies not expressed in hertz
Even higher frequencies are believed to occur naturally, in the frequencies of the quantum-mechanical wave functions of high-energy (or, equivalently, massive) particles, although these are not directly observable, and must be inferred from their interactions with other phenomena. For practical reasons, these are typically not expressed in hertz, but in terms of the equivalent energy.
| This SI unit is named after Heinrich Rudolf Hertz. As with all SI units whose names are derived from the proper name of a person, the first letter of its symbol is uppercase (Hz). When an SI unit is spelled out in English, it should always begin with a lowercase letter (hertz), except for at the beginning of a sentence or in capitalized material such as a title. Note that "degree Celsius" conforms to this rule because of the "d".
— Based on The International System of Units, section 5.2. |
References
See also
- Frequency changer
- Orders of magnitude (frequency)
- Signal bandwidth
- Radian per second
External links
- BIPM Cesium ion fCs definition
- National Research Council of Canada: Generation of the Hz
- National Research Council of Canada: Cesium fountain clock
- National Physical Laboratory: Trapped ion optical frequency standards
- National Research Council of Canada: Optical frequency standard based on a single trapped ion
- National Research Council of Canada: Optical frequency comb
Source: adapted by the editor from Wikipedia, the free encyclopedia; from the article "Hertz". Image Credit.
