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An optical medium is material through which electromagnetic waves propagate. It is a form of transmission medium. The permittivity and permeability of the medium define how electromagnetic waves propagate in it. The medium has an ''intrinsic impedance'', given by :: where and are the electric field and magnetic field, respectively. In a region with no electrical conductivity, the expression simplifies to: :: For example, in free space the intrinsic impedance is called the characteristic impedance of vacuum, denoted ''Z''0, and :: Waves propagate through a medium with velocity , where is the frequency and is the wavelength of the electromagnetic waves. This equation also may be put in the form : where is the angular frequency of the wave and is the wavenumber of the wave. In electrical engineering, the symbol , called the ''phase constant'', is often used instead of . The propagation velocity of electromagnetic waves in free space, an idealized standard reference state (like absolute zero for temperature), is conventionally denoted by ''c''0:〔With ISO 31-5, NIST and the BIPM have adopted the notation ''c''0.〕 : :where is the electric constant and is the magnetic constant. For a general introduction, see Serway〔 〕 For a discussion of man-made media, see Joannopoulus.〔 〕 ==Notes and references== 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「Optical medium」の詳細全文を読む スポンサード リンク
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