millivolt n : a unit of potential equal to one thousandth of a volt [syn: mV]
The volt (symbol: V) is the SI derived unit of electric potential difference or electromotive force. It is named in honor of the Lombard physicist Alessandro Volta (1745–1827), who invented the voltaic pile, the first modern chemical battery.
DefinitionThe volt is defined as the potential difference across a conductor when a current of one ampere dissipates one watt of power. Hence, it is the base SI representation m2 · kg · s-3 · A-1, which can be equally represented as one joule of energy per coulomb of charge, J/C.
- \mbox = \dfrac = \dfrac = \dfrac = \dfrac = \dfrac
Josephson junction definitionSince 1990 the volt is maintained internationally for practical measurement using the Josephson effect, where a conventional value is used for the Josephson constant, fixed by the 18th General Conference on Weights and Measures as
- K = 0.4835979 GHz/µV.
Hydraulic analogyIn the hydraulic analogy sometimes used to explain electric circuits by comparing them to water-filled pipes, voltage is likened to water pressure – it determines how fast the electrons will travel through the circuit. Current (in amperes), in the same analogy, is a measure of the volume of water that flows past a given point per unit time (volumetric flow rate). The flow rate is determined by the width of the pipe (analogous to electrical resistance) and the pressure difference between the front end of the pipe and the exit (potential difference or voltage). The analogy extends to power dissipation: the power given up by the water flow is equal to flow rate times pressure, just as the power dissipated in a resistor is equal to current times the voltage drop across the resistor (amperes x volts = watts).
The relationship between voltage and current (in ohmic devices) is defined by Ohm's Law.
Nominal voltages of familiar sources:
- Nerve cell action potential: around 75 mV
- Single-cell, rechargeable NiMH or NiCd battery: 1.2 V
- Mercury battery: 1.355 V
- Single-cell, non-rechargeable alkaline battery (e.g. AAA, AA, C and D cells): 1.5 V
- Lithium polymer rechargeable battery: 3.75 V
- Transistor-transistor logic/CMOS (TTL) power supply: 5 V
- PP3 battery: 9 V
- Automobile electrical system: "12 V", about 11.8 V discharged, 12.8 V charged, and 13.8-14.4 V while charging (vehicle running).
- Household mains electricity: 240 V RMS in Australia, 230 V RMS in Europe, Asia and Africa, 120 V RMS in North America, 100 V RMS in Japan (see List of countries with mains power plugs, voltages and frequencies)
- Rapid transit third rail: 600 to 750 V (see List of current systems for electric rail traction)
- High speed train overhead power lines: 25 kV RMS at 50 Hz, but see the list of current systems for electric rail traction for exceptions.
- High voltage electric power transmission lines: 110 kV RMS and up (1150 kV RMS was the record as of 2005)
- Lightning: Varies greatly, often around 100 MV.
Note: Where 'RMS' (root mean square) is stated above, the peak voltage is \sqrt times greater than the RMS voltage for a sinusoidal signal centered around zero voltage.
History of the voltIn 1800, as the result of a professional disagreement over the galvanic response advocated by Luigi Galvani, Alessandro Volta developed the so-called Voltaic pile, a forerunner of the battery, which produced a steady electric current. Volta had determined that the most effective pair of dissimilar metals to produce electricity was zinc and silver. In the 1880s, the International Electrical Congress, now the International Electrotechnical Commission (IEC), approved the volt for electromotive force. At that time, the volt was defined as the potential difference across a conductor when a current of one ampere dissipates one watt of power.
Prior to the development of the Josephson junction voltage standard, the volt was maintained in national laboratories using specially constructed batteries called standard cells. The United States used a design called the Weston cell from 1905 to 1972.
millivolt in Tosk Albanian: Volt
millivolt in Arabic: فولت
millivolt in Asturian: Voltiu
millivolt in Bengali: ভোল্ট
millivolt in Min Nan: Bó͘-lú-to͘h
millivolt in Bosnian: Volt
millivolt in Breton: Volt
millivolt in Bulgarian: Волт
millivolt in Catalan: Volt
millivolt in Czech: Volt
millivolt in Danish: Volt
millivolt in German: Volt
millivolt in Estonian: Volt
millivolt in Modern Greek (1453-): Βολτ
millivolt in Spanish: Voltio
millivolt in Esperanto: Volto
millivolt in Basque: Volt
millivolt in French: Volt
millivolt in Friulian: Volt
millivolt in Gan Chinese: 伏
millivolt in Galician: Volt
millivolt in Korean: 볼트
millivolt in Croatian: Volt
millivolt in Indonesian: Volt
millivolt in Icelandic: Volt
millivolt in Italian: Volt
millivolt in Hebrew: וולט
millivolt in Kurdish: Volt
millivolt in Latin: Voltium
millivolt in Latvian: Volts
millivolt in Lithuanian: Voltas
millivolt in Hungarian: Volt
millivolt in Macedonian: Волт
millivolt in Malay (macrolanguage): Volt
millivolt in Dutch: Volt (eenheid)
millivolt in Japanese: ボルト (単位)
millivolt in Norwegian: Volt
millivolt in Norwegian Nynorsk: Volt
millivolt in Polish: Wolt
millivolt in Portuguese: Volt
millivolt in Kölsch: Volt (Mohß)
millivolt in Romanian: Volt
millivolt in Russian: Вольт
millivolt in Scots: Volt
millivolt in Simple English: Volt
millivolt in Slovak: Volt
millivolt in Slovenian: Volt
millivolt in Serbian: Волт
millivolt in Serbo-Croatian: Volt
millivolt in Finnish: Voltti
millivolt in Swedish: Volt
millivolt in Tamil: வோல்ட்டு
millivolt in Thai: โวลต์
millivolt in Vietnamese: Vôn
millivolt in Turkish: Volt
millivolt in Ukrainian: Вольт
millivolt in Contenese: 伏
millivolt in Chinese: 伏特