CBSE Class 10 Science 2020 · Paper 31/3/3 · Question 22

(a) 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, $\frac{\sin i}{\sin r}=\text{constant}$. This constant is the refractive index of the second medium with respect to the first. (b) Labelled ray diagram (see the figure): the incident ray strikes the top face at O at angle of incidence $i$ and bends towards the normal NN′, with angle of refraction $r<i$; the refracted ray OO′ meets the bottom face at O′ and bends away from the normal MM′, leaving as the emergent ray at angle of emergence $e=i$. So the emergent ray is parallel to the incident ray, and the perpendicular distance $d$ between the incident ray produced and the emergent ray is the lateral displacement.