# 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)

2019年新國際單位製中，真空磁導率不是確定值。它的CODATA 2019推荐值是

${\displaystyle \mu _{0}\approx 1.25663706212(19)\times 10^{-6}\,{\textrm {H}}\cdot {\textrm {m}}^{-1}}$

${\displaystyle \mathbf {B} =\mu _{0}\ \mathbf {H} .}$

## 由電流單位安培定義真空磁导率

${\displaystyle |{\boldsymbol {F}}_{m}|={\mu _{0} \over 2\pi }{|{\boldsymbol {I}}|^{2} \over |{\boldsymbol {r}}|}.}$

${\displaystyle \mu _{0}=4\pi \times 10^{-7}({\rm {{N/A^{2}})\approx 1.2566370614\cdots \times 10^{-6}({\rm {{N/A^{2}})}}}}}$[1]

## 單位系統及曾定義過的μ0數值

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

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

## 在電磁學中的重要性

${\displaystyle {\boldsymbol {H}}={{\boldsymbol {B}} \over \mu _{0}}-{\boldsymbol {M}},}$

${\displaystyle c_{0}={1 \over {\sqrt {\mu _{0}\varepsilon _{0}}}}.}$

## 參考資料

1. Magnetic constant. Fundamental Physical Constants. Committee on Data for Science and Technology. 2006 [2010-02-04]. （原始内容存档于2007-08-20） –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. （原始内容存档于2020-11-27）.
3. ^ This choice defines the SI unit of current, the ampere: Unit of electric current (ampere). Historical context of the SI. NIST. [2007-08-11]. （原始内容存档于2017-04-25）.
4. ^ 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
5. ^ SUNAMCO. Recommended values of the fundamental physical constants. Symbols, Units, Nomenclature and Fundamental Constants in Physics (PDF) http://metrology.files.wordpress.com/2010/12/6_recommended_fundamental_constants_iupap_sunamco_red_book_1987.pdf. 1987: 54 [2015-03-05]. （原始内容存档 (PDF)于2020-05-08）. 缺少或|title=为空 (帮助); (the IUPAP "Red book").
6. ^ 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.
7. ^ For an introduction to the subject of choices for independent units, see John David Jackson. Classical electrodynamics Third. New York: Wiley. 1998: 154 [2015-03-07]. ISBN 0-471-30932-X. （原始内容存档于2009-08-04）.
8. ^ The decision to explicitly include the factor of 2π in km stems from the "rationalization" of the equations used to describe physical electromagnetic phenomena.
9. ^ Unit of electric current (ampere). Historical context of the SI. NIST. [2007-08-11]. （原始内容存档于2017-04-25）.
10. ^ 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]
11. ^ MIST speed of light in vacuum. [2015-03-07]. （原始内容存档于2017-06-25）.
12. ^ The exact numerical value is found at: Electric constant, ε0. NIST reference on constants, units, and uncertainty: Fundamental physical constants. NIST. [2012-01-22]. （原始内容存档于2007-04-23）. 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 (PDF). Rev Mod Phys. April–June 2008, 80 (2): 633–729 [2015-03-07]. Bibcode:2008RvMP...80..633M. . doi:10.1103/RevModPhys.80.633. （原始内容 (PDF)存档于2011-08-05）.