_____ of the sound beam occurs whenever there is both oblique incidence and a difference in media propagation speeds.

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

Answer: (D)

Refraction is the bending of the sound beam as it passes into another medium at an oblique angle when the speeds of sound differ between the two media. Because the wave travels at different speeds, the transmitted wavefronts must realign, so the transmitted ray changes direction according to Snell’s law. The frequency stays the same, but the wavelength adjusts in the new medium, causing the beam to bend rather than continue straight or bounce back. This differs from reflection, which involves energy returning toward the source, and from diffraction or scattering, which involve bending around obstacles or redirection caused by inhomogeneities.