A narrow beam of white light is shown to pass through a triangular glass prism. After passing through the prism, it produces a specturm XY on a screen.
(a) State the colour seen at `X and Y`.
(b) Why do different colours of white light bend through different angles with respect to the incident beam of light ?
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Explanation

(a) Colour seen at `X` is violet, and colour seen at `Y` is red.
(b) Different colours bend through different angles because speed of different colour through glass is different and hence refraction index of glass for different colours is different.