What is the term for the bending of a wave when it enters a medium where its speed is different?

The term for the bending of a wave when it enters a medium where its speed is different is known as refraction. This phenomenon occurs because waves travel at different speeds in different media. When a wave, such as light or sound, moves from one medium to another (for example, from air into water), its speed changes, leading to a change in direction. This bending effect is governed by Snell's law, which relates the angles of incidence and refraction to the speeds of the wave in the respective media.

Refraction is a fundamental concept in optics and wave behavior, illustrating how waves interact with various substances. Understanding refraction is crucial in applications such as lens design, optical instruments, and even understanding natural phenomena like rainbows.

In contrast, reflection involves waves bouncing off a surface, diffraction pertains to the spreading of waves around obstacles, and transmission refers to the passage of waves through a medium without bending. Each of these terms describes different behaviors of waves, but refraction specifically captures the bending due to a change in wave speed, making it the correct choice.