What phenomenon causes a rainbow when light passes through a prism?

• A. Refraction
• B. Absorption
• C. Diffraction
• D. Dispersion

Answer: (D)

Dispersion is at work here—the separation of white light into its colors due to wavelength-dependent bending in a medium. When light enters a prism, different wavelengths travel at different speeds, so each color experiences a different refractive index. Shorter wavelengths (toward blue/violet) bend more; longer wavelengths (toward red) bend less. As the light exits the prism, these varying bending angles spread the colors apart, producing a rainbow-like spectrum. Refraction alone would bend light but not separate colors; absorption would remove some wavelengths; diffraction involves interference from edges or slits. The key idea is that the prism causes colors to refract by different amounts, i.e., dispersion.