What term describes the bending of the sound beam when it crosses an interface with different propagation speeds at a non-perpendicular angle?

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

Answer: (A)

Refraction is the bending of a sound beam when it passes into a medium with a different propagation speed at an angle to the interface. The wave must adjust its direction so that the component of its phase along the boundary remains continuous, which changes the transmitted beam’s angle according to the speeds in the two media. Because the speed changes, the wavelength also changes while frequency stays the same. If the incidence were perpendicular to the interface, there would be no bending—just a speed (and wavelength) change. Attenuation and absorption involve loss of amplitude, not direction, and reflection involves energy bouncing back rather than refracting through.