Electric constant: Difference between revisions
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Revision as of 20:44, 19 February 2010
The electric constant (also: vacuum permittivity), designated ε0, is a physical constant appearing in equations relating electrical charge to mechanical quantities, for example in Coulomb's law. In scalar form, Coulomb's law can be given as:
- ,
where F is the magnitude of the force between two point charges q and Q, separated by a distance r.
Its value is given by
- ,
where c is the speed of light in vacuum and μ0 is the magnetic constant. In the SI system of units, c is defined and μ0 is a consequence of the definition of the ampere: μ0 = 4π × 10−7 N/A2. Consequently, ε0 is exact and expressed up to ten digits by:
Terminology
Historically, the physical constant ε0 has had different names. One of these was dielectric constant of vacuum.[2] Although still in use,[3] "dielectric constant" is now deemed obsolete.[4][5] In the 1987 IUPAP Red book this constant was called permittivity of vacuum.[6] Currently the nomenclature is electric constant.[1][7] The vacuum permittivity ε = εr ε0 is equal to the electric constant ε0.
Footnotes
- ↑ 1.0 1.1 CODATA. Electric constant. 2006 CODATA recommended values. NIST. Retrieved on 2007-08-08.
- ↑ King, Ronold W. P. (1963). Fundamental Electromagnetic Theory. New York: Dover, p. 139.
- ↑ for example in this random patent
- ↑ IEEE Standards Board (1997). IEEE Standard Definitions of Terms for Radio Wave Propagation p. 6.
- ↑ Braslavsky, S.E. (2007), "Glossary of terms used in photochemistry (IUPAC recommendations 2006)", Pure and Applied Chemistry 79: p. 324.
- ↑ SUNAMCO Commission (1987), Recommended values of the fundamental physical constants, Symbols, Units, Nomenclature and Fundamental Constants in Physics, at p.54; (the IUPAP "Red book").
- ↑ National Physical Laboratory, UK (1998). Fundamental Physical Constants p. 2.