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The hertz (symbol Hz) is the SI unit of frequency. It is named in honour of the German physicist Heinrich Rudolf Hertz who made some important contributions to science in the field of electromagnetism.

One hertz simply means "one (event) per second"; 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. The reciprocal of frequency is time (period); a frequency of 1 Hz is equivalent to a period of 1 second, a frequency of 1 MHz to a period of 1 microsecond. In older writings, e.g., pre-WWII articles about radio transmissions and its electronics, the older but similar unit cycles per second (cps) is seen, along with related multiples kilocycles, megacycles, and so forth.

1 SI Multiples

2 Examples

• 50 Hz or 60 Hz, electromagnetic — standard AC mainsMains power plug & socket The term mains usually refers to the domestic AC electrical power supply (as in "I've connected the appliance to the mains"). The term is not usually used in the US and Canada. See also List of countries with mains power plugs, v powerLund, Sweden Electric power often known as power or electricity involves the production and delivery of electrical energy in sufficient quantities to operate domestic appliances, office equipment, industrial machinery and provide sufficient energy for bot
• 20 Hz to ~16 kHz, acousticAcoustics is a branch of physics and is study of sound, mechanical waves in gases, liquids, and solids. A scientist who works in the field of acoustics is an acoustician . The application of acoustics in technology is called acoustical engineering. There — normal range of adult human hearing (most children and some animals perceive sounds outside this range)
• 261.626 Hz, acoustic — the musical note middle CIn music, the term middle C refers to the pitch-class "C" located between the staves of the grand staff. When calculated in equal temperament with a reference of A above middle C as 440 Hz, the frequency of the middle C note is approximately 261. 625565 H
• 440 Hz, acoustic — concert pitchIn music, pitch refers to the perception of the frequency of a note. For example, the A above middle C is nowadays set at (often written as "A 440 Hz", and known as concert pitch , although this has not always been the case (see #Historical pitch standard (A above middle C), used for tuning musical instruments
• 740 kHz, transitions — the clock speed of the world's first commercial microprocessorIntel 80486DX2 and an Intel 80386 A microprocessor (abbreviated as P or uP is an electronic computer central processing unit (CPU) made from miniaturized transistors and other circuit elements on a single semiconductor integrated circuit (IC) (aka microch, the Intel 4004The Intel 4004 a 4-bit CPU, was the world's first single- chip microprocessor, as well as the first commercial one. At about the same time, some other integrated circuit CPU designs, such as the military F14 CADC of 1970, were implemented as chipsets, i. ( 1971)
• 1 MHz to 8 MHz, transitions — clock speeds of early home/ personal computers (mid- 1970s to mid- 1980s)
• 30 MHz to 300 MHz, electromagnetic — VHF terrestrial TV broadcasts
• 88 MHz to 108 MHz, electromagnetic — FM radio broadcasts
• 1420 MHz, the spectral frequency of hydrogen, the most common element in the universe.
• 3.4 GHz, transitions — clock speed of the Pentium 4 "Prescott" microprocessor ( 2004)
• 428 THz to 750 THz, electromagnetic — visible light, from red to violet
• 30 PHz, electromagnetic — x-rays