The refractive index of a material depends on the wavelength of light passing through it. When white light enters a material like glass or water, each wavelength interacts differently with the atoms of the material. Shorter wavelengths, such as violet and blue, typically experience a higher refractive index than longer wavelengths, like red. This means shorter wavelengths slow down more than longer ones.
As light slows down, it bends or refracts. Because shorter wavelengths are slowed more, they bend more sharply than longer wavelengths. This unequal bending of different colors causes the light to spread out, a phenomenon known as dispersion. The material’s internal structure and the frequency of the incoming wave determine how much the refractive index changes with wavelength.
When light passes through a prism or lens, this bending effect separates the white light into its individual colors. Each color takes a slightly different path due to the variation in speed caused by the wavelength-dependent refractive index. This behavior is crucial in optical systems and explains why dispersion occurs in materials.