Weber (unit): Difference between revisions
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The '''weber''' (symbol Wb) is the [[SI]] unit of [[magnetic flux]]. It is named for the German physicist [[Wilhelm Eduard Weber]]. | The '''weber''' (symbol Wb) is the [[SI]] unit of [[magnetic flux]]. It is named for the German physicist [[Wilhelm Eduard Weber]]. | ||
The ninth CGPM (''Conférence Générale des Poids et Mesures'', General Conference on Weights and Measures) ratified in 1948 a definition based on [[Faraday's law (electromagnetism)|Faraday's law]] for magnetic induction. This law connects electromotive force <math> | The ninth CGPM (''Conférence Générale des Poids et Mesures'', General Conference on Weights and Measures) ratified in 1948 a definition based on [[Faraday's law (electromagnetism)|Faraday's law]] for magnetic induction. This law connects electromotive force <math> \mathcal{E}</math>, (in volt), to the rate of change of magnetic flux <math>\Phi\,</math> (in Wb/s). | ||
:<math> | :<math> | ||
\mathcal{E} = -\frac{d\Phi}{dt} | \mathcal{E} = -\frac{d\Phi}{dt} | ||
</math> | </math> | ||
If Φ is linear in time—then Φ changes with a uniform rate in time—and if Φ = 0 at ''t'' = 0, then | If the magnetic flux Φ is linear in time—then Φ changes with a uniform rate in time—and if Φ = 0 at ''t'' = 0, then | ||
:<math> | :<math> | ||
\Phi(t) = - t\, \mathcal{E} | \Phi(t) = - t\, \mathcal{E} | ||
</math> | </math> | ||
This equation forms the basis of the formal definition, wich reads: | This equation forms the basis of the formal definition, wich reads: | ||
''One weber is the magnetic flux which, 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.'' (Resolution 2, International Committee for Weights and Measures. 1946)<ref> | ''One weber is the magnetic flux which, 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.'' (Resolution 2, International Committee for Weights and Measures. 1946).<ref> | ||
[http://www.bipm.org/utils/common/pdf/si_brochure_8_en.pdf BIPM brochure about SI]. PDF page 52; paper page 144.</ref> | [http://www.bipm.org/utils/common/pdf/si_brochure_8_en.pdf BIPM brochure about SI]. PDF page 52; paper page 144.</ref> | ||
Wb = V⋅s = N⋅m⋅A<sup>−1</sup> = kg⋅A<sup>−1</sup>⋅s<sup>−2</sup>⋅m<sup>2</sup> = T⋅m<sup>2</sup>, where A stands for [[ampere]], T for [[tesla]], V for [[volt]], and N for [[newton]]. | :Wb = V⋅s = N⋅m⋅A<sup>−1</sup> = kg⋅A<sup>−1</sup>⋅s<sup>−2</sup>⋅m<sup>2</sup> = T⋅m<sup>2</sup>, | ||
where A stands for [[ampere]], T for [[tesla]], V for [[volt]], and N for [[newton]]. | |||
==Reference== | ==Reference== | ||
Revision as of 11:25, 7 July 2009
The weber (symbol Wb) is the SI unit of magnetic flux. It is named for the German physicist Wilhelm Eduard Weber.
The ninth CGPM (Conférence Générale des Poids et Mesures, General Conference on Weights and Measures) ratified in 1948 a definition based on Faraday's law for magnetic induction. This law connects electromotive force , (in volt), to the rate of change of magnetic flux (in Wb/s).
If the magnetic flux Φ is linear in time—then Φ changes with a uniform rate in time—and if Φ = 0 at t = 0, then
This equation forms the basis of the formal definition, wich reads: One weber is the magnetic flux which, 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. (Resolution 2, International Committee for Weights and Measures. 1946).[1]
- Wb = V⋅s = N⋅m⋅A−1 = kg⋅A−1⋅s−2⋅m2 = T⋅m2,
where A stands for ampere, T for tesla, V for volt, and N for newton.
Reference
- ↑ BIPM brochure about SI. PDF page 52; paper page 144.