In ultrasound physics, which phenomenon describes bending of waves as they pass between media with different propagation speeds?

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

Answer: (A)

Bending of waves when they cross boundaries where the speed of sound changes is refraction. In ultrasound, sound travels at different speeds in different tissues (for example, faster in muscle, slower in fat, much faster in bone). When the beam hits an interface at an angle, the transmitted part changes direction according to Snell’s law, causing the path to bend. This is distinct from reflection (energy bouncing back to the transducer), diffraction (bending around edges or through apertures), and attenuation (loss of signal strength from absorption and scattering).