CBSE Class 10 Science 2020 · Paper 31/2/3 · Question 29(a)

(a) At the top face the ray bends towards the normal ($\angle r<\angle i$); at the bottom face it bends away from the normal and emerges with $\angle e=\angle i$, so the emergent ray is parallel to the incident ray but shifted sideways. The perpendicular distance $d$ between the incident ray produced and the emergent ray is the lateral displacement, as shown in the completed diagram. (b) The absolute refractive index of a medium is the ratio of the speed of light in vacuum (or air) to the speed of light in that medium: $n_m=\frac{c}{v}$. (c) Mirror 1 is a concave mirror, since its image is virtual, erect and enlarged; use: shaving mirror or dentist's mirror (also reflectors in torches, searchlights and vehicle headlights, and solar furnaces). Mirror 2 is a convex mirror, since its image is virtual, erect and diminished; use: rear-view mirror in vehicles (also security mirrors).