Volt
The volt is the SI derived unit of electric potential difference or electromotive force . It is named in honor of the
Italian physicist Alessandro Volta , who invented the
voltaic pile, the first chemical battery.
Encyclopedia
The
volt is the SI derived unit of electric potential difference or electromotive force . It is named in honor of the
Italian physicist Alessandro Volta , 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.
.
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 = 0.4835979 GHz/µV.
Common voltages
Nominal voltages of familiar sources:
Note: Where 'RMS' is stated above, the peak voltage is times higher than the RMS voltage.
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 , 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.
Notes
See also
- SI for unit prefixes
- SI electromagnetism units
