What term best describes the reflection that occurs when the interface is large and smooth?

• A. Specular reflection
• B. Nonspecular reflection
• C. Scattering
• D. Refraction

Answer: (A)

Specular reflection occurs when the interface is large and smooth relative to the wavelength, so incident light reflects in a single, well-defined direction with the angle of reflection equal to the angle of incidence. The surface acts like a mirror, producing a clear image because the reflected rays are coherent and not scattered. If the surface were rough on that scale, reflection would become nonspecular (diffuse), scattering light in many directions and ruining the image. Scattering and refraction describe different phenomena—diffuse light spread or bending of light as it passes into another medium, respectively—so they don’t fit the description of a mirror-like reflection.