Volt
Encyclopedia : V : VO : VOL : Volt
The volt (symbol: V) is the SI derived unit of electric potential difference or electromotive force Rudolf F. Graf, "Volt", Dictionary of Electronics; Radio Shack, 1974-75. Fort Worth, Texas. ISBN B000AMFOZY . It is named in honor of the Italian physicist Alessandro Volta (1745–1827), who invented the voltaic pile, the first chemical battery.
Definition
The 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 = \mbox \cdot \mbox^ = \mbox \cdot \mbox^ = \mbox^2 \cdot \mbox \cdot \mbox^ \cdot \mbox^].
- K = 0.4835979 GHz/µV.
Common voltages
Nominal voltages of familiar sources:
- Nerve cell action potential: 40 millivolts
- Single-cell, rechargeable alkaline battery: 1.2 volts
- Single-cell, non-rechargeable battery (e.g. AAA, AA, C and D cells): 1.5 volts
- Lithium polymer rechargeable battery: 3.7 volts
- Transistor-Transistor Logic Level: 5 volts
- Automobile electrical system: 12 volts
- Household mains electricity: 240 volts Australia, 120 volts North America, 230 volts Europe List of countries with mains power plugs, voltages and frequencies
- Rapid transit third rail: 600 to 700 volts List of current systems for electric rail traction
- High voltage electric power transmission lines: 110 kilovolts and up (1150 kV is the record as of 2005)
- Lightning: Varies greatly, often around 100 megavolts.
History of the volt
In 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. 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.
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| This SI unit is named after Alessandro Volta. As for all SI units whose names are derived from the proper name of a person, the first letter of its symbol is uppercase (V). But when an SI unit is spelled out, it should always be written in lowercase (volt), unless it begins a sentence or is the name "degree Celsius". — Based on [The International System of Units], section 5.2.
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Notes
See also
- SI for unit prefixes
- SI electromagnetism units
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