Volt

From Free net encyclopedia

Image:NISTvoltChip.jpg The volt (symbol: V) is the SI derived unit of electric potential difference or voltage. It is named in honor of the Italian physicist Alessandro Volta (1745–1827), who invented the voltaic pile, the first chemical battery.

1 Definition
2 Common voltages
3 History of the volt
4 Notes
5 See also

[edit]

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.

1 V = 1 W/A = 1 J/C = 1 m²·kg·s^–3·A^–1

Since 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_{J-90} = 0.4835979 GHz/µV.

[edit]

Common voltages

Image:BateriaR14.jpg 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 Template:Ref
Rapid transit third rail: 600 to 700 volts Template:Ref
High voltage electric power transmission lines: 110 kilovolts and up (1150 kV is the record as of 2005)
Lightning: 100 megavolts

[edit]

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.

Template:SI unit lowercase

[edit]

Notes

[edit]

Volt

From Free net encyclopedia

Contents

Definition

Common voltages

History of the volt

Notes

See also

Views

Personal tools

Search

Partner sites