PHYSICS · Single correct · CBSE · Physics · Light — Reflection and Refraction · Light — Reflection and Refraction
Problem
Two matte boards, X and Y, have identical chemical composition but different microscopic roughness. Board X has peak-to-valley variations of 0.1 mm, whereas board Y has variations of 0.5 mm. A laser beam strikes each board at normal incidence. A photodetector is positioned 30° above the surface normal, 2.0 m from the point of incidence. Which statement best compares the power detected when each board is illuminated?
(a) The detector receives more power from board X; its smoother surface produces a narrow specular lobe that still encompasses the detector at 30∘.
(b) The detector receives the same power from both boards because both surfaces are sufficiently rough to behave as diffuse (Lambertian) reflectors.
(c) The detector receives no power from either board because truly diffuse scattering sends no light into a single, well–defined direction.
(d) The detector receives more power from board Y; its larger roughness means each facet reflects more light, increasing the total reflected power.