Question

A prism ABC (with BC as base) is placed in different orientations. A narrow beam of white light is incident on the prism as shown in figure. In which of the following cases, after dispersion, the third colour from the top corresponds to the colour of the sky?

A. (a) B. (c) C. (c) D. (d)

Answer 1

The colour of sky is blue. The colour having the maximum wavelength is deviated the least. The deviation is towards the base of the prism. The white light consist of seven colours red, orange, yellow, green, blue, indigo, violet .violet is deviated the most and red the least. Blue is the third colour starting from violet. So we see that image B has based on the top hence having colours in such an order that blue is the third. Hence option B is correct.