Question

Comment on the statement: ‘When any ray of white light is incident on a glass prism, it simply disperses it into its seven constituent colours.

Answer 1

Before making any comment, the following simple experiment should be performed.

Arrangement is shown in the diagram. P₁ and P₂ are two glass prisms exactly similar and placed at some distance from each of the such that their refracting surfaces are parallel to each other and the base of the prism P₂ is upwards and vertex downwards. S is a narrow slit through which a ray of white light is incident on the refracting face of the prism P₁. It is dispersed by it into its seven constituent colours.
When this dispersed light falls on the refracting surface of the prism P₂, having its base upwards so that the rays have deviated in a direction different from the first, we see on the screen only a white spot of light. It is evident that the second prism P₂ recombines these colours to form white light acting as a ‘recombination prism’ while the first prism acts as a ‘dispersing prism’.