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.
gigavolt in Tosk Albanian: Volt
gigavolt in Arabic: فولت
gigavolt in Asturian: Voltiu
gigavolt in Bengali: ভোল্ট
gigavolt in Min Nan: Bó͘-lú-to͘h
gigavolt in Bosnian: Volt
gigavolt in Breton: Volt
gigavolt in Bulgarian: Волт
gigavolt in Catalan: Volt
gigavolt in Czech: Volt
gigavolt in Danish: Volt
gigavolt in German: Volt
gigavolt in Estonian: Volt
gigavolt in Modern Greek (1453-): Βολτ
gigavolt in Spanish: Voltio
gigavolt in Esperanto: Volto
gigavolt in Basque: Volt
gigavolt in French: Volt
gigavolt in Friulian: Volt
gigavolt in Gan Chinese: 伏
gigavolt in Galician: Volt
gigavolt in Korean: 볼트
gigavolt in Croatian: Volt
gigavolt in Indonesian: Volt
gigavolt in Icelandic: Volt
gigavolt in Italian: Volt
gigavolt in Hebrew: וולט
gigavolt in Kurdish: Volt
gigavolt in Latin: Voltium
gigavolt in Latvian: Volts
gigavolt in Lithuanian: Voltas
gigavolt in Hungarian: Volt
gigavolt in Macedonian: Волт
gigavolt in Malay (macrolanguage): Volt
gigavolt in Dutch: Volt (eenheid)
gigavolt in Japanese: ボルト (単位)
gigavolt in Norwegian: Volt
gigavolt in Norwegian Nynorsk: Volt
gigavolt in Polish: Wolt
gigavolt in Portuguese: Volt
gigavolt in Kölsch: Volt (Mohß)
gigavolt in Romanian: Volt
gigavolt in Russian: Вольт
gigavolt in Scots: Volt
gigavolt in Simple English: Volt
gigavolt in Slovak: Volt
gigavolt in Slovenian: Volt
gigavolt in Serbian: Волт
gigavolt in Serbo-Croatian: Volt
gigavolt in Finnish: Voltti
gigavolt in Swedish: Volt
gigavolt in Tamil: வோல்ட்டு
gigavolt in Thai: โวลต์
gigavolt in Vietnamese: Vôn
gigavolt in Turkish: Volt
gigavolt in Ukrainian: Вольт
gigavolt in Contenese: 伏
gigavolt in Chinese: 伏特