Refraction occurs when light travels from one transparent medium to another at a different speed. Experiments have shown that light refraction follows a set of rules.
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Refraction of light ray
The following are the laws of refraction of light. 
  1. The incident ray, the refracted ray and the normal ray to the interface of two transparent media at the point of incidence all lie in the same plane.
  2. The ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant for the light of a given colour and the given pair of media. This law is also known as Snell’s law of refraction. (This is true for angle \(0°< i < 90°\))
If \(i\) is the angle of incidence and \(r\) is the angle of refraction, then

This constant value is called the refractive index of the second medium with respect to the first. The below table gives the refractive index or absolute refractive index of different materials.
Absolute refractive index of different materials
Let us study the detailed information about refractive index in the next section.