A handheld flashlight shines white light onto a brick wall whose surface texture can…
PHYSICS · Multi-part · CBSE · Physics · Light — Reflection and Refraction · Light — Reflection and Refraction
Problem
A handheld flashlight shines white light onto a brick wall whose surface texture can be considered randomly rough on the scale of visible wavelengths. An observer slowly walks leftward and rightward in a plane parallel to the wall while keeping a fixed distance of 2m from the illuminated spot.
Respond to the following prompts about what the observer sees and why.
(a) Describe qualitatively how the apparent brightness of the illuminated spot changes (if at all) as the observer moves through a horizontal angular range of ±45∘ measured from the direction of the incident beam.
(b) Using physical reasoning, explain why the brightness pattern you described in part (a) is produced by the wall even though the law of reflection states that a single angle of reflection should exist for each incident ray.
(c) Suppose the same wall were polished to a mirror-like finish without altering its chemical composition. Predict how the observer’s brightness experience would differ from that in part (a) and provide a brief explanation based on surface normals.