Snell’s Law explains the behavior of light in a prism by describing how light bends when it enters and exits the prism’s surfaces due to changes in refractive index.
- Entry into the prism:
When light enters the prism from air, it moves from a less dense medium (air) to a denser medium (glass or plastic). According to Snell’s Law, the light bends toward the normal at the surface because it slows down. - Dispersion inside the prism:
White light is made of multiple wavelengths (colors). Since the refractive index of the prism varies with wavelength, each color bends by a different amount. Violet bends more than red, causing the light to spread into a spectrum. - Exit from the prism:
As the light leaves the prism and moves back into air (a lower refractive index), it bends away from the normal. The different colors continue to separate even more as they exit. - Resulting spectrum:
The combination of bending on both entry and exit—governed by Snell’s Law—and the wavelength-dependent refraction causes the light to emerge from the prism as a spread of colors, forming a visible rainbow-like spectrum.
Thus, Snell’s Law explains how light changes direction and separates into colors when passing through a prism.