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Medium (optics)

Free space is the most simple and elementary electromagnetic medium. A medium is the stuff that waves propagate through. The properties, permittivity and permeability, define how electromagnetic waves travel through a medium. Also, the medium has an intrinsic impedance:

\eta = \sqrt{\mu \over \varepsilon}

where μ is the permeability of the medium and \varepsilon is the permittivity of the medium.

Waves propagate through a medium with velocity of cw. Simply the propagation velocity of a wave in a given medium is just the wavelength multiplied by its frequency, or its the angular frequency divided by the wavenumber(physics) or phase constant(electrical engineering).

~ c_w = \nu \lambda ~
c_w = {\omega \over k} = {\omega \over \beta}

The propagation velocity of electromagnetic waves in free space (medium) is

c_w = {1 \over \sqrt{\varepsilon_0 \mu_0}}
where, ~ \varepsilon_0 ~ is the vacuum permittivity of free space
~ \mu_0 ~ is the vacuum permeability of free space.


See also: Electromagnetic spectrum, Electromagnetic radiation, Optics.

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