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In physics, the fine-structure constant, also known as Sommerfeld's constant, commonly denoted ''α'' (the Greek letter ''alpha''), is a fundamental physical constant characterizing the strength of the electromagnetic interaction between elementary charged particles. It is related to the elementary charge (the electromagnetic coupling constant) ''e'', which characterizes the strength of the coupling of an elementary charged particle with the electromagnetic field, by the formula . Being a dimensionless quantity, it has the same numerical value in all systems of units. Arnold Sommerfeld introduced the fine-structure constant in 1916. ==Definition== Some equivalent definitions of ''α'' in terms of other fundamental physical constants are: : where: * ''e'' is the elementary charge; * ''ħ'' = ''h''/2π is the reduced Planck constant; * ''c'' is the speed of light in vacuum; * ''ε''0 is the electric constant or permittivity of free space; * ''µ''0 is the magnetic constant or permeability of free space; * ''k''e is the Coulomb constant; * ''R''K is the von Klitzing constant. The definition reflects the relationship between ''α'' and the electromagnetic coupling constant ''e'', which equals . 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Fine-structure constant」の詳細全文を読む スポンサード リンク
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