Which phenomenon refers to the change in direction of waves when they enter a different medium?

The phenomenon of waves changing direction upon entering a different medium is known as refraction. This occurs because waves travel at different speeds in different materials. When a wave crosses the boundary between two media, such as from air into water, its speed changes and this alteration in speed causes the wave to bend.

The degree of bending depends on the indices of refraction of the two materials involved. Snell's Law mathematically describes this bending and provides a way to predict the angle at which the wave will travel in the new medium. Refraction is a fundamental concept in wave physics, relevant in various contexts, including optics and sound.

Understanding refraction is crucial for applications such as the design of lenses, fiber optics, and understanding natural phenomena like the bending of light from the sun as it enters the Earth's atmosphere.