Fig. shows a light (blue + red + green) incident on a prism and on a parallel sided glass slab. Complete the diagrams by drawing the refracted and the emergent rays.
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Explanation

The completed ray diagrams are shown in Fig. 6.4.
In a prism, refraction takes place at two inclined surfaces, so the prism causes dispersion and deviation of light into its constituent colours and a spectrum is seen.
In case of a parallel sided glass slab, refraction takes place at two parallel surfaces. On the first surface, the colours are separated due to different deviation for the rays of different colours i.e., dispersion takes place. On the second surface, the ray of each colour is refracted such that the emergent ray is parallel to the incident ray on the first surface. Since there is no further separation of colours due to refraction at the second surface (as it is in case of the prism), so the emergent coloured rays are parallel to each other and they are so close that it is difficult to see the separate colours and the emergent light appears to be almost white (= blue + red + green).