A boundary roughness tends to cause which phenomenon?

• A. Refraction
• B. Absorption
• C. Denial
• D. Scattering

Answer: (D)

Boundary roughness causes scattering because irregularities on a surface disrupt the orderly reflection of a wave. When the features of the boundary are comparable to or larger than the wavelength, the incident wave is reflected in many different directions rather than in a single, mirror-like path. That redistribution of energy is what we call scattering, producing diffuse echoes and speckle in imaging. If the boundary were perfectly smooth (roughness very small compared to the wavelength), the reflection would be mostly specular, with a clearer, single direction. Refraction would occur from a smooth boundary due to a change in wave speed across media, not because of surface texture. Absorption involves energy loss to the medium (heating, etc.), not the directional spread caused by roughness. Denial isn’t a wave phenomenon.