When a beam of white light is passed through a triangular glass prism, it gets dispersed into its seven colour components. Why do we get these colours ? In the given figure, the colours 3 and 4 represent the extreme components of the spectrum. Identify 3 and 4.

Explanation

(i) Different colours of light travel with different speeds while passing through a prism. Hence, they are bent at different angles with respect to the incident ray. This leads to the dispersion of light.
(ii) X = violet, Y = red.