# Laws of Refraction

First Law

When refraction takes place, the incident ray, the refracted ray and the normal to the refracting surface at the point of incidence lie in the same plane.

In Figure 9.18, AO, OB and NONÂ´ are in the same plane.

Second Law (Snellâ€™s Law)

When refraction takes place, the ratio of the sine of angle of incidence to the sine of angle of refraction is a constant for a given pair of media and for light of a given wavelength.

This constant is called refractive index denoted by Î¼. Therefore,