Question

A beam of light, consisting of red, green and blue colours, is incident on a right-angled prism, as shown. the refractive indices of the material of the prism for the above red, green and blue wavelengths are 1.39 1.44 and 1.47 respectively. The prism will :

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A

separate part of the red colour from the green and blue colours

B

separate part of the blue colour from the red and green colours

C

separate all the three colours from one another

D

not separate even partially any colour from the other tow colours

Medium

Solution

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Correct option is A)

The angle of incidence of all the rays is at the hypotenuse. For a critical angle of , the refractive index must be 


For red light, . hence, its critical angles are <. therefore, red light will pass through the surface into air.

For green and blue lights, . Hence, their critical angles are . They will be reflected internally and emerge from the surface at the bottom.

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