Which term describes the bending of a wave at a boundary between media with different propagation speeds?

• A. Reflection
• B. Diffraction
• C. Refraction
• D. Attenuation

Answer: (C)

Refraction happens when a wave crosses from one medium to another with a different propagation speed. The frequency stays the same, but the speed changes, so the wave’s direction must shift to fit across the boundary. That change in direction is the bending we call refraction. A classic example is light entering water from air: it slows down and bends toward the normal. If the wave enters a slower medium, it bends toward the normal; into a faster medium, it bends away from the normal. Reflection, by contrast, is when part of the wave bounces back into the original medium; diffraction is bending around obstacles or through openings; attenuation is the loss of amplitude as it travels.