What term describes the change of speed when waves pass through different media?

The correct term that describes the change of speed when waves pass through different media is refraction. Refraction occurs when a wave, such as light or sound, travels from one medium into another that has a different density or properties. As the wave enters the new medium, its speed changes, which causes the wave to change direction. This bending of the wave is what we observe as refraction.

For instance, when light moves from air into water, it slows down and bends at the interface, resulting in the phenomenon we commonly observe with objects seeming to be in a different position when viewed through water. This concept is fundamental in various applications, including optics, which involve lenses and prisms.

The other terms represent different phenomena. Diffraction pertains to the bending of waves around obstacles and the spreading out of waves as they pass through openings. Reflection involves the bouncing back of waves when they hit a barrier or boundary, while dispersion refers to the process where waves of different frequencies (like colors of light) spread apart as they travel through a medium, often seen in a prism. However, none of these accurately describe the change of speed specifically due to a medium transition, which is why refraction is the correct answer.