A light ray strikes a perfectly polished metal plate at an angle of $35^{c}irc$ to the normal. Determine the angle of reflection and explain why the reflected ray does not change direction if the plate is roughened, and what effect roughness would have on the reflected light.

Step-by-step solution

1. By the law of reflection, the angle of incidence equals the angle of reflection: both are $35^{c}irc$ relative to the normal.
2. When the plate is perfectly polished, all reflected rays are parallel, giving a sharp image (specular reflection).
3. If the plate is roughened, the microscopic facets are oriented randomly, so incident rays are reflected in many directions.
4. This random distribution of reflected angles causes diffuse reflection, making the surface appear matte and eliminating a sharp image.

Concept tested: Law of reflection and surface roughness

Published 10 October 2026 · How this solution was prepared and checked