Lights flash at frequency f = 0.5 Hz (Hz = hertz), 1.0 Hz and 2.0 Hz, where Failed to parse (Missing texvc executable; please see math/README to configure.): x

Hz means Failed to parse (Missing texvc executable; please see math/README to configure.): x
flashes per second. T is the period and T = Failed to parse (Missing texvc executable; please see math/README to configure.): y
s (s = second) means that Failed to parse (Missing texvc executable; please see math/README to configure.): y

is the number of seconds per flash. T and f are each other's reciprocal: f = 1/T and T = 1/f.

The hertz (symbol Hz) is the SI unit of frequency defined as the number of cycles per second of a periodic phenomenon.^[1] One of its most common uses is the description of the sine wave, particularly those used in radio and audio applications. The word "hertz" is named for Heinrich Rudolf Hertz, who was the first to conclusively prove the existence of electromagnetic waves.

Definition[link]

The hertz is equivalent to cycles per second.^[2] In defining the second, the CIPM declared that "the standard to be employed is the transition between the hyperfine levels F = 4, M =  0 and F = 3, M = 0 of the ground state 2S_1/2 of the cesium 133 atom, unperturbed by external fields, and that the frequency of this transition is assigned the value 9 192 631 770 hertz"^[3] thereby effectively defining the hertz and the second simultaneously.

In English, hertz is used as a plural.^[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 "frequency" (activity) of aperiodic or stochastic events, such as radioactive decay, is expressed in becquerels.

Even though angular velocity, angular frequency and hertz all have the dimensions of 1/s, angular velocity and angular frequency are not expressed in hertz,^[5] 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 are:

Failed to parse (Missing texvc executable; please see math/README to configure.): \omega = 2\pi f \,

and Failed to parse (Missing texvc executable; please see math/README to configure.): f = \frac{\omega}{2\pi} \, 

. This SI unit is named after Heinrich Hertz. As with every International System of Units (SI) unit whose name is derived from the proper name of a person, the first letter of its symbol is upper case (Hz). When an SI unit is spelled out in English, it should always begin with a lower case letter (hertz), except where any word would be capitalized, such as at the beginning of a sentence or in capitalized material such as a title. Note that "degree Celsius" conforms to this rule because the "d" is lowercase. —Based on The International System of Units, section 5.2.

History[link]

The hertz is named after the German physicist Heinrich Hertz who made important scientific contributions to the study of electromagnetism. The name was established by the International Electrotechnical Commission (IEC) in 1930.^[6] 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.

The term "gigahertz", most commonly used in computer processor clock rates and radio frequency (RF) applications, can be pronounced either /ˈɡɪɡəhɜrts/, with a hard /ɡ/ sound, or /ˈdʒɪɡəhɜrts/, with a soft /dʒ/^[7] (see giga-#Pronunciation). The prefix "giga-" is derived directly from the Greek "γιγας" ("giant").

Applications[link]

Sine waves of different frequency.

Details of a heartbeat as an example of a non-sinusoidal periodic phenomenon that can be described in terms of hertz. Two complete cycles are illustrated.

Vibration[link]

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 20 Hz to 20,000 Hz; the average adult human can hear sounds between 20 Hz and 16,000 Hz.^[8] The range of ultrasound, high-intensity infrasound and other physical vibrations such as molecular vibrations extends into the megahertz range and well beyond.

Electromagnetic radiation[link]

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. (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[link]

In computing, most central processing units (CPU) are labeled in terms of their clock rate expressed in megahertz or gigahertz (10⁶ or 10⁹ hertz, respectively). This number refers to the frequency of the CPU's master clock signal ("clock rate"). This signal is simply an electrical voltage which changes from low to high and back again at regular intervals. This signal is a square wave. Hertz has become the primary unit of measurement accepted by the general populace to determine the performance of a CPU, but many experts have criticized this approach, which they claim is an easily manipulable benchmark.^[9] For home-based personal computers, the CPU has ranged from approximately 1 megahertz in the late 1970s (Atari, Commodore, Apple computers) to up to 6 GHz in the present (IBM POWER processors) and up to 8 GHz overclocked (AMD FX processors).^[10]

Various computer buses, such as the front-side bus connecting the CPU and northbridge, also operate at different frequencies in the megahertz range

[edit] SI multiples

Frequencies not expressed in hertz[link]

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 quantum energy, which is proportional to the frequency by the factor of Planck's constant.

See also[link]

References[link]

External links[link]

• BIPM Cesium ion f_Cs 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
• One Hertz in Radians per Second (Google). Note, as of 06 May 2009 there is an error of 2Failed to parse (Missing texvc executable; please see math/README to configure.): \pi

.

v t e SI units Base units Ampere · Candela · Kelvin · Kilogram · Metre · Mole · Second Derived units Becquerel · Coulomb · Degree Celsius · Farad · Gray · Henry · Hertz · Joule · Katal · Lumen · Lux · Newton · Ohm · Pascal · Radian · Siemens · Sievert · Steradian · Tesla · Volt · Watt · Weber Accepted for use with SI Dalton (Atomic mass unit) · Astronomical unit · Day · Decibel · Degree Celsius · Degree of arc · Electronvolt · Hectare · Hour · Litre · Minute · Minute of arc · Neper · Second of arc · Tonne Atomic units · Natural units See also SI prefixes · Systems of measurement · Conversion of units · New SI definitions · History of the metric system Book:International System of Units  · Category:SI base units

This biographical article needs additional citations for verification. Please help by adding reliable sources. Contentious material about living persons that is unsourced or poorly sourced must be removed immediately, especially if potentially libelous or harmful. (July 2011)

Leo Andanar Lastimosa (born on September 26, 1964) is a radio and television newscaster in Cebu, Philippines. He currently co-anchors TV Patrol Central Visayas with Atty. Haide Acuña. He is also the host of Arangkada over radio station DYAB and a columnist in Cebu's newspaper The Freeman, He is a main regional reporter in Iba-Balita and Iba-Balita Ngayon on Studio 23. as well as a Mass Communications professor in St. Theresa's College. He started his broadcast career in 1984 with DYLA-AM as a campus reporter while studying in USJ-R, Cebu City.

In June 2011, besides newscasting and writing for The Freeman, Leo ventured into music, writing the lyrics for what would be Cebu musical icon Emilio Villareal's last composition and now the theme song of Jose R. Gullas Halad Museum, titled Awit Ni Dodong [4].

Present Positions[link]

• Anchorman, Arangkada (DYAB AM)
• Anchorman, TV Patrol Central Visayas (Channel 3)
• Manager, DYAB AM
• Columnist, The Freeman Cebu
• Faculty, Saint Theresa's College, Cebu City (STC)
• Exec. Chairman, KBP Cebu
• Main Regional Reporter, Iba-Balita (Studio 23)
• Main Regional Reporter, Iba-Balita Ngayon (Studio 23)

Former Positions[link]

• Anchor, Banat Visayas, Sulong Mindanao!, ABS-CBN Regional Network Group (RNG), 1996
• News Director, DYLA, VIMCONTU Broadcasting System, 1985–1991
• News Director, DYRF, Catholic Media Network (CMN), 1991–1995

Awards[link]

• Best TV Newscaster, The 14th Golden Dove Awards of the Kapisanan ng mga Brodkaster ng Pilipinas (KBP)
• Garbo Sa Sugbo, by the Cebu Provincial Government in the field of broadcast journalism and television
• Outstanding Talisaynon, by the Talisay City Government in the field of media.
• Hall of Fame, Radio News Category, Cebu Archdiocesan Mass Media Awards (CAMMA)
• Hall of Fame, Radio Commentary Category, Cebu Archdiocesan Mass Media Awards (CAMMA)
• Finalist, Column Writing Category, Cebu Archdiocesan Mass Media Awards (CAMMA)
• Special Citation, Kasayurang Kinuykoyan, National Press Club (NPC), 1991
• Best Public Affairs Program (Arangkada), KBP Golden Dove Awards, 1998
• Best Public Affairs Program Host, KBP Golden Dove Awards, 2002
• Best Commentary Program (Kuwentas Klaras), KBP Golden Dove Awards, 2002
• Best TV News Program, Catholic Mass Media Awards (CMMA-Manila), 2005
• Best TV Newscaster, KBP Golden Dove Awards, 2005
• Outstanding Talisaynon Award, 2006
• Garbo Sa Sugbo Awardee, August 2006

Cases[link]

• Civil case for damages filed by Cebu Gov. Gwendolyn Garcia in 2007 in Barili Regional Trial Court. RTC Judge Leopoldo Cañete dismissed it in April 2008. ^[1]
• Criminal case for libel filed by Cebu Governor Gwendolyn Garcia in 2007 in the Cebu City Prosecutor's Office. Cebu City RTC Judge Geraldine Faith Econg dismissed the case after Gov. Garcia withdrew the same. ^[2]
• Criminal case for libel filed by Cebu Governor Gwendolyn Garcia in 2007 in the Cebu City Prosecutor's office. The case will be handled by Cebu City RTC Judge Rafael Yrastorza. ^[3]

References[link]

External links[link]

• Profile on Google Docs
• Profile on Scribd

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