Question

You are given prisms made of crown glass and flint glass with a wide variety of angles. Suggest a combination of prisms which will (a) deviate a pencil of white light without much dispersion, (b) disperse (and displace) a pencil of white light without much deviation.

Answer 1

a)

The value of the angular dispersion produced by the two different prisms should be zero so that, there is no dispersion is takes place.

Here, if we place the two prisms beside each other and consider their bases are on the opposite side of the incident white light, with their faces touching each other. When this dispersed light is incident on the first prism, it will recombine and white light will emerge from the combination of the two prisms.

b)

Take the system of the two prisms as suggested in the answer (a). Adjust (increases) the angle of the flint-glass-prism so that the deviations due to the combination of the prisms become equal. This combination will disperse the pencil of light without much deviation.