Which optical phenomenon describes light bending as it passes from one medium to another?

Refraction is the optical phenomenon that describes the bending of light as it passes from one medium to another. This bending occurs because light travels at different speeds in different materials. For instance, when light transitions from air into water, it slows down due to the higher density of water compared to air, causing it to change direction.

The degree of bending is determined by the angle at which the light strikes the interface between the two media and the indices of refraction of the materials involved. This phenomenon is fundamental in optics and is crucial for the functioning of lenses, where it is utilized to focus light for vision correction and other applications.

Other options reflect different optical behaviors. Reflection involves the bouncing of light off a surface rather than changing mediums, diffraction concerns the spreading of light waves around obstacles, and dispersion refers to the separation of light into its constituent colors due to varying speeds in a medium. Refraction is uniquely characterized by the bending of light due to changes in speed as it crosses into a different material.