Snell's Law - Engineering LibreTexts

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Speed of Light and Index of Refraction

Refraction occurs because the speed of the light changes when it passes into a new medium. The speed of light in a medium is given by the following equation:

\[c=nv\]

where n is the refractive index of the material and c is the speed of light in a vacuum. The refractive index can also be determined from the permittivity and permeability of the material. Therefore it is possible to know the optical properties of the material from the electrical properties of the material. Using these properties, the index of refraction is given by the following equation:

\[n=\dfrac{c}{v}=\sqrt{\dfrac{\varepsilon \mu }{\varepsilon_{0} \mu_{0}}}=\sqrt{\varepsilon_{r} \mu_{r}}\]

where εr and μr are the permativity and permeability of the material respectively. Table 1 lists the index of refraction for some common materials.

Table 1: Index of Refraction for Selected Materials
Vacuum 1.000
Air 1.000293
Water 1.333
Ice 1.309
Plexiglass 1.49
Soda-Lime Glass 1.46
Diamond 2.42

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