CBSE Class 10 Science 2019 · Paper 31/1/1 · Question 13

A rainbow is a natural spectrum of sunlight that appears in the sky after a rain shower, as an arc of seven colours. It is caused by the dispersion of sunlight by tiny water droplets in the atmosphere, which act like small prisms, and it is always formed in the direction opposite to the Sun. Labelled diagram (see the figure): a ray of sunlight (white light) falls on a raindrop; (1) it is refracted and dispersed as it enters the drop; (2) it is reflected internally at the back of the drop; (3) it is refracted and dispersed again as it comes out, so the colours emerge separated, red and violet at different angles, toward an observer who has the Sun behind.