CBSE Class 10 Science 2019 · Paper 31/4/2 · Question 3(a)

(i) 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. (ii) Second law (Snell's law): For light of a given colour and a given pair of media, the ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant, $\frac{\sin i}{\sin r}=\text{constant}$. This constant is the refractive index of the second medium with respect to the first, $n_{21}$.