Which phenomenon involves the change in direction of a wave as it passes from one medium to another?

Refraction is the phenomenon that describes the change in direction of a wave as it passes from one medium to another. This change occurs because waves travel at different speeds in different materials. When a wave moves from a medium with one density to another with a different density (such as from air to water), its speed changes, causing it to bend and alter its directional path. This bending of the wave is most commonly observed with light waves, although sound waves can also exhibit refraction.

The process of refraction follows Snell's Law, which quantitatively relates the angle of incidence and refraction to the indices of refraction of the two media involved. This principle is fundamental in fields such as optics, where it is crucial for understanding how lenses work and how light behaves in various substances.