CBSE Class 10 Science 2018 · Paper 31(B)/C · Question 20(a)

(a) Laws of refraction of light: (i) The incident ray, the refracted ray and the normal to the interface of the two transparent media at the point of incidence all lie in the same plane. (ii) 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: $\frac{\sin i}{\sin r}=\text{constant}$ (Snell's law of refraction). (b) The absolute refractive index of a medium is the ratio of the speed of light in vacuum to the speed of light in that medium: $n_m=\frac{c}{v}$. (c) For glass, $c=n_g\times v_g=1.5\times 2\times 10^8=3\times 10^8$ m/s. For diamond, $v_d=\frac{c}{n_d}=\frac{3\times 10^8}{2.42}\approx 1.24\times 10^8$ m/s.