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Asked in RS Academy GUJCET booklet · Refractive index and dielectric constant
Idea: the speed of an electromagnetic wave in a medium is v = 1/(√με), and in vacuum c = 1/(√μ₀ε₀).
The refractive index is the ratio of the two speeds: n = c/v = √(με)/(μ₀ε₀) = √μᵣεᵣ.
The dielectric constant K is another name for the relative permittivity εᵣ.
So n = √μᵣ K.
For most transparent materials μᵣ is very nearly 1, which is why the optical index is usually quoted as just √K.
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