CBSE Class 10 Science 2018 · Paper 31/1 · Question 11(a)

First law: the incident ray, the refracted ray and the normal to the interface of the two media at the point of incidence all lie in the same plane. Second law (Snell's law): the ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant for light of a given colour and for the given pair of media, $\frac{\sin i}{\sin r}=\text{constant}$. Absolute refractive index of a medium: the refractive index of the medium with respect to vacuum. It is the ratio of the speed of light in vacuum to the speed of light in the medium: $n_m=\frac{\text{speed of light in vacuum}}{\text{speed of light in the medium}}=\frac{c}{v}$.