CBSE Class 10 Science 2017 · Paper 31/1/C · Question 10

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 a given pair of media. Mathematically: $\frac{\sin i}{\sin r}=\text{constant}=n_{21}$, the refractive index of the second medium with respect to the first. Absolute refractive index: $n_m=\frac{c}{v}$, where $c$ is the speed of light in vacuum ($3\times 10^8$ m/s) and $v$ is the speed of light in the medium.