CBSE Class 10 Science 2020 · Paper 31/4/1 · Question 24

Place the second prism, identical to the first, in an inverted position (upside down) with respect to the first prism and close to it, so that the band of colours from the first prism falls on it. The first prism disperses the narrow beam of white light into its colours (violet bent the most, red the least); the inverted prism bends each colour back through the same angle in the opposite direction, so all the colours emerge together, parallel to the incident beam, and recombine into white light on the screen. The labelled ray diagram shows white light, ${\text{P}}_1$, the inverted ${\text{P}}_2$, the rays R and V, the emergent white light and the screen.