Question

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? [NCERT Exemplar Problems]

Answer 1

Answer:

When the prism is placed with angle A in the upward direction, the third colour from top is yellow(refer image A). But we have been given the third color from top is that is blue( colour of the sky).

Thus, base BC must be on the top that is the prism must be inverted.