What phenomenon describes the bending of a wave due to a change in its speed?

Refraction is the phenomenon that describes the bending of a wave when it crosses into a medium where its speed changes. This behavior occurs because waves travel at different speeds in different materials. For example, light travels faster in air than in water. When light enters water from air, it slows down, causing it to bend at the interface between the two mediums. This bending effect can be observed in everyday situations, such as when a straw appears to be bent when placed in a glass of water.

In summary, refraction occurs because the wave's speed changes as it moves between different mediums, leading to a change in direction. This principle is central to the understanding of optics and is crucial in applications such as lens design, fiber optics, and various scientific fields.