The given ray diagram shows the dispersion of a light ray through a triangular prism, with colours labelled X (upper) and Y (lower) after the prism. Identify colours X and Y and explain why Y bends more than X.

Question

Accepted Answer

X (bending least, appearing on the upper part of the spectrum) is red light; Y (bending most, appearing on the lower part) is violet light. Violet light has a shorter wavelength than red light, and travels more slowly through glass. Since the amount of bending (refraction) depends on the change in speed, violet light — with the greater change in speed relative to its speed in air — bends more than red light, which has the smallest change in speed.