# 真空磁导率

µ0 = ×10−7 V·s/(A·m)
1.2566370614...×10−6 H·m−1N·A−2T·m/A 或 Wb/(A·m)

$\mathbf{B} = \mu_0 \ \mathbf{H}.$

## 由電流單位安培定義真空磁导率

$|\boldsymbol{F}_m|={\mu_0\over2\pi}{|\boldsymbol{I}|^2\over|\boldsymbol{r}|}.$

$\mu_0 = 4 \pi \times 10^{-7} (\rm{N / A ^2} ) \approx 1.2566370614 \cdots \times 10 ^{-6} (\rm{N / A ^2} )$[7][8]

## 單位系統及曾定義過的μ0數值

$F_{\mathrm{m}} \propto \frac {I^2} {r}. \;$

$F_{\mathrm{m}} = k_{\mathrm{m}} \frac {I^2} {r}. \;$

## 在電磁學中的重要性

$\boldsymbol{H}={\boldsymbol{B}\over\mu_0}-\boldsymbol{M},$

$c_0={1\over\sqrt{\mu_0\varepsilon_0}}.$

## 參考資料

1. ^ Magnetic constant. Fundamental Physical Constants. Committee on Data for Science and Technology. 2006 [2010-02-04] —通过National Institute of Standards and Technology.
2. ^ Rosen, Joe. Permeability (Physics). Encyclopedia of Physics. Facts on File science library. New York: Facts On File. 2004 [2010-02-04]. ISBN 9780816049745.（需註冊）
3. ^ Magnetic constant. Fundamental Physical Constants. Committee on Data for Science and Technology. 2006 [2010-02-04] —通过National Institute of Standards and Technology.
4. ^ Rosen, Joe. Permeability (Physics). Encyclopedia of Physics. Facts on File science library. New York: Facts On File. 2004 [2010-02-04]. ISBN 9780816049745.（需註冊）
5. ^ This choice defines the SI unit of current, the ampere: Unit of electric current (ampere). Historical context of the SI. NIST. [2007-08-11].
6. ^ See for example Tipler, Paul A. Physics for Scientists and Engineers, Third Edition, Extended Version. New York, NY: Worth Publishers. 1992: 826. ISBN 0-87901-434-2.Equation 25-14
7. ^ Magnetic constant. 2006 CODATA recommended values. NIST. [2007-08-08].
8. ^ 8.0 8.1 CODATA Recommended Values of the Fundamental Physical Constants: 2006. Committee on Data for Science and Technology (CODATA): See Table 1. NIST.
9. ^ SUNAMCO. Recommended values of the fundamental physical constants (PDF). Symbols, Units, Nomenclature and Fundamental Constants in Physics. 1987: 54.; (the IUPAP "Red book").
10. ^ J R Lalanne, F Carmona & L Servant. Optical spectroscopies of electronic absorption. World Scientific series in contemporary chemical physics, vol. 17. Singapore;London: World Scientific. 1999: 10. ISBN 981-02-3861-4.
11. ^ For an introduction to the subject of choices for independent units, see John David Jackson. Classical electrodynamics Third. New York: Wiley. 1998: 154. ISBN 0-471-30932-X.
12. ^ The decision to explicitly include the factor of 2π in km stems from the "rationalization" of the equations used to describe physical electromagnetic phenomena.
13. ^ Unit of electric current (ampere). Historical context of the SI. NIST. [2007-08-11].
14. ^ The magnetic permeability of a realizable vacuum (such as outer space, or ultra-high vacuum), which is measurable at least in principle, is distinct from the defined parameter μ0.[來源請求]
15. ^ MIST speed of light in vacuum
16. ^ The exact numerical value is found at: Electric constant, ε0. NIST reference on constants, units, and uncertainty: Fundamental physical constants. NIST. [2012-01-22]. This formula determining the exact value of ε0 is found in Table 1, p. 637 of PJ Mohr, BN Taylor, DB Newell. Table 1: Some exact quantities relevant to the 2006 adjustment in CODATA recommended values of the fundamental physical constants: 2006. Rev Mod Phys. April–June 2008, 80 (2): 633–729. arXiv:0801.0028. Bibcode:2008RvMP...80..633M. doi:10.1103/RevModPhys.80.633.