Which color of white light bends the most when refracted by a prism?

• A. Violet
• B. Red
• C. Green
• D. Yellow

Answer: (A)

Dispersion is being tested here: white light is made of many colors, and a prism bends each color by a different amount because the refractive index of the glass varies with wavelength. When light enters the prism from air, it changes direction according to Snell’s law, and the amount of bending depends on how high the color’s index is inside the material. Violet light has the largest refractive index in typical glass, so its path changes the most and it emerges with the greatest angle of deviation. Red light has the smallest index, so it bends the least, with green and yellow in between. So violet ends up bending the most.