Weber (unit)

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Weber
Unit systemSI derived unit
SymbolWb 
Named afterWilhelm Eduard Weber
In SI base units:kgm2s−2A−1

In physics, the weber (/ˈvb-, ˈwɛb.ər/ VAY-, WEH-bər;[1][2] symbol: Wb) is the SI derived unit of magnetic flux. A flux density of one Wb/m2 (one weber per square metre) is one tesla.

The weber is named after the German physicist Wilhelm Eduard Weber (1804–1891).

Definition[edit]

SI multiples of weber (Wb)
Submultiples Multiples
Value SI symbol Name Value SI symbol Name
10−1 Wb dWb deciweber 101 Wb daWb decaweber
10−2 Wb cWb centiweber 102 Wb hWb hectoweber
10−3 Wb mWb milliweber 103 Wb kWb kiloweber
10−6 Wb µWb microweber 106 Wb MWb megaweber
10−9 Wb nWb nanoweber 109 Wb GWb gigaweber
10−12 Wb pWb picoweber 1012 Wb TWb teraweber
10−15 Wb fWb femtoweber 1015 Wb PWb petaweber
10−18 Wb aWb attoweber 1018 Wb EWb exaweber
10−21 Wb zWb zeptoweber 1021 Wb ZWb zettaweber
10−24 Wb yWb yoctoweber 1024 Wb YWb yottaweber
Common multiples are in bold face.

The weber may be defined in terms of Faraday's law, which relates a changing magnetic flux through a loop to the electric field around the loop. A change in flux of one weber per second will induce an electromotive force of one volt (produce an electric potential difference of one volt across two open-circuited terminals).

Officially:

The weber is commonly expressed in a multitude of other units:

where Wb = weber,
Ω = ohm,
C = coulomb,
V = volt,
T = tesla,
J = joule,
m = metre,
s = second,
A = ampere,
H = henry,
Mx = maxwell.

This SI unit is named after Wilhelm Eduard Weber; as with every International System of Units (SI) unit named for a person, the first letter of its symbol is upper case (Wb). However, when an SI unit is spelled out in English, it is treated as a common noun and should always begin with a lower case letter (weber)—except in a situation where any word in that position would be capitalized, such as at the beginning of a sentence or in material using title case.

History[edit]

In 1861, the British Association for the Advancement of Science (known as "The BA"[4]) established a committee under William Thomson (later Lord Kelvin) to study electrical units.[5] In a February 1902 manuscript, with handwritten notes of Oliver Heaviside, Giovanni Giorgi proposed a set of rational units of electromagnetism including the weber, noting that "the product of the volt into the second has been called the weber by the B. A."[6]

The International Electrotechnical Commission began work on terminology in 1909 and established Technical Committee 1 in 1911, its oldest established committee,[7] "to sanction the terms and definitions used in the different electrotechnical fields and to determine the equivalence of the terms used in the different languages."[8]

In 1930, TC1 decided that the magnetic field strength (H) is of a different nature from the magnetic flux density (B),[9] and took up the question of naming the units for these fields and related quantities, among them the integral of magnetic flux density.[citation needed]

In 1935, TC 1 recommended names for several electrical units, including the weber for the practical unit of magnetic flux (and the maxwell for the CGS unit).[9][10]

Also in 1935, TC1 passed responsibility for "electric and magnetic magnitudes and units" to the new TC24; this "led eventually to the universal adoption of the Giorgi system, which unified electromagnetic units with the MKS dimensional system of units, the whole now known simply as the SI system (Système International d’unités)."[12]

In 1938, TC24 "recommended as a connecting link [from mechanical to electrical units] the permeability of free space with the value of µ0 = 4π×107 H/m. This group also recognized that any one of the practical units already in use (ohm, ampere, volt, henry, farad, coulomb, and weber), could equally serve as the fourth fundamental unit.[9] "After consultation, the ampere was adopted as the fourth unit of the Giorgi system in Paris in 1950."[11]

Notes and references[edit]

  1. ^ Wells, John (3 April 2008). Longman Pronunciation Dictionary (3rd ed.). Pearson Longman. ISBN 978-1-4058-8118-0.
  2. ^ "weber (main entry is American English, Collins World English (further down) is British)". Dictionary.com.
  3. ^ "CIPM, 1946: Resolution 2 / Definitions of Electrical Units". International Committee for Weights and Measures (CIPM) Resolutions. International Bureau of Weights and Measures (BIPM). 1946. Retrieved 2008-04-29.
  4. ^ "The BA (British Association for the Advancement of Science)". Cite web requires |website= (help)
  5. ^ Frary, Mark. "In the beginning...The world of electricity: 1820-1904". International Electrotechnical Commission. Retrieved 2018-04-19. Cite web requires |website= (help)
  6. ^ Giorgi, Giovanni (February 1902). "Rational Units of Electromagnetism" (Manuscript with handwritten notes by Oliver Heaviside). p. 9. Retrieved 2014-02-21. Cite web requires |website= (help)
  7. ^ "Strategic Policy Statement, IEC Technical Committee on Terminology" (PDF). International Electrotechnical Commission. Archived from the original (PDF) on 2006-09-04. Retrieved 2008-04-29. Cite uses deprecated parameter |dead-url= (help); Cite web requires |website= (help)
  8. ^ "IEC Technical Committee 1". International Electrotechnical Commission. Retrieved 2018-04-19. Cite web requires |website= (help)
  9. ^ a b c d "The role of the IEC / Work on quantities and units". History of the SI. International Electrotechnical Commission. Archived from the original on 25 Sep 2013. Retrieved 2018-04-19. Cite uses deprecated parameter |dead-url= (help)
  10. ^ "Summary: Electrical Units". IEC History. International Electrotechnical Commission. Retrieved 2018-04-19.
    This page incorrectly states that the units were established in 1930, since that year, TC 1 decided "that the question of names to be allocated to magnetic units should not be considered until general agreement had been reached on their definitions" [1]
  11. ^ a b Ruppert, Louis (1956). Brief History of the International Electrotechnical Commission (PDF). International Electrotechnical Commission. p. 5. Retrieved 2018-04-19.
  12. ^ Raeburn, Anthony. "Overview: IEC technical committee creation: the first half-century (1906-1949)". International Electrotechnical Commission. Retrieved 2018-04-19. Cite web requires |website= (help)