Law 1.

The incident ray, the normal and the refracted ray all lie in the same plane.

Law 2.

The ratio sine of the angle of incidence (i)
               sine of the angle of refraction (r)

is constant for light of a given colour (frequency) crossing the boundary of two given media. This ratio is called the refractive index (n).

     n = sin i
           sin r

The refractive index of a transparent substance is measured when light enters the substance from a vacuum, but for all practical purposes we can take it as light entering the substance from air. The greater the value of the refractive index, the greater the bending of the light. Refraction is caused by the fact that light travels at different speeds in different media and it can also be shown that the refractive index is equal to the ratio of the speeds in the two media.

Refractive index of glass = speed of light in air
                                         speed of light in glass

Some common refractive indices:

• water - 1.33
• alcohol - 1.36
• ice - 1.31
• perspex - 1.49
• diamond - 2.42
• paraffin - 1.44
• glass(crown) - 1.52

The refraction of light is explained by the fact that light has a wave nature.