Weber (unit)

Definition

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:{{cquote|Weber (unit of magnetic flux) — The weber is the magnetic flux that, linking a circuit of one turn, would produce in it an electromotive force of 1 volt if it were reduced to zero at a uniform rate in 1 second.{{cite web |archive-url = https://web.archive.org/web/20201125164459/http://www.bipm.org/en/CIPM/db/1946/2/ |access-date = 2008-04-29 |archive-date = 2020-11-25 |url-status = dead That is: \mathrm{Wb} = \mathrm{V}{\cdot}\mathrm{s}.

One weber is also the total magnetic flux across a surface of one square meter perpendicular to a magnetic flux density of one tesla; that is, \mathrm{Wb} = \mathrm{T}{\cdot}\mathrm{m}^2.

Expressed only in SI base units, 1 weber is: \mathrm{Wb} = \dfrac{\mathrm{kg}{\cdot}\mathrm{m}^2}{\mathrm{s}^2{\cdot}\mathrm{A}}.

The weber is used in the definition of the henry as 1 weber per ampere, and consequently can be expressed as the product of those units: \mathrm{Wb} = \mathrm{H}{\cdot}\mathrm{A}.

The weber is commonly expressed in a multitude of other units: \mathrm{Wb} =\Omega {\cdot} \text{C} =\dfrac{\mathrm{J}}{\mathrm{A}} =\dfrac{\mathrm{N}{\cdot}\mathrm{m}}{\mathrm{A}},

where Ω is ohm, C is coulomb, J is joule, and N is newton.

History

In 1861, the British Association for the Advancement of Science (known as "The BA" |access-date = 2018-04-19 |archive-date = 2018-04-18 |archive-url = https://web.archive.org/web/20180418105621/http://www.iec.ch/about/history/beginning/ |url-status = dead |access-date = 2014-02-21 |archive-date = 2019-10-29 |archive-url = https://web.archive.org/web/20191029134329/https://www.iec.ch/about/history/documents/documents_giovanni.htm |url-status = dead

The International Electrotechnical Commission began work on terminology in 1909 and established Technical Committee 1 in 1911, its oldest established committee, |archive-url = https://web.archive.org/web/20060904211154/http://www.iec.ch:80/cgi-bin/getsps.pl/1.pdf?file=1.pdf |url-status = dead |archive-date = 2006-09-04 |access-date = 2008-04-29 |access-date = 2018-04-19

|archive-url = https://web.archive.org/web/20070611071833/http://www.iec.ch/zone/si/si_role.htm |archive-date = 11 June 2007 |url-status=dead |access-date = 2018-04-19

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

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).{{cite web |access-date = 2018-04-19 |archive-date = 2018-04-20 |archive-url = https://web.archive.org/web/20180420010525/http://www.iec.ch/about/history/overview/history_summary.htm |url-status = dead :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" http://www.iec.ch/zone/si/si_role.htm

|access-date = 2018-04-19 |archive-date = 2016-12-24 |archive-url = https://web.archive.org/web/20161224053025/http://www.iec.ch/about/history/documents/pdf/IEC%20History%201906-1956.pdf |url-status = dead

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 ()."{{cite web |access-date = 2018-04-19

In 1938, TC24 "recommended as a connecting link [from mechanical to electrical units] the permeability of free space with the value of 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. "After consultation, the ampere was adopted as the fourth unit of the Giorgi system in Paris in 1950."

Multiples

Like other SI units, the weber can be modified by adding a prefix that multiplies it by a power of 10.

Conversions

• One maxwell (Mx), the CGS unit of magnetic flux, equals 10−8 Wb

References

1. Wells, John. (3 April 2008). "Longman Pronunciation Dictionary". Pearson Longman.
2. "weber (main entry is American English, Collins World English (further down) is British)".