Velocity v, of electromagnetic radiation

It is perhaps worthwhile to mention that the velocity (v) of electromagnetic radiation decreases as it passes through a condensed medium (e.g., a liquid or solution). The ratio of its speed in a vacuum (c) to its velocity in the medium is called the index of refraction (n) of the medium ... 

The permittivity Spm and magnetic permeability p of a medium together determine the velocity v of electromagnetic radiation through that medium ... 

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See also in sourсe #XX -- [ ]

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