Physics
Physics
Problem
A glass slide has surface irregularities of average height 30 nm. Determine whether incident red light of wavelength 630 nm will predominantly undergo specular or diffuse reflection from the slide. Briefly justify your answer with a numerical comparison.Intuitive explanation
The key is comparing surface roughness to wavelength using the Rayleigh criterion for smooth vs. rough surfaces. When surface irregularities are much smaller than the incident wavelength, the surface appears optically smooth and reflects light specularly (like a mirror). When roughness approaches or exceeds the wavelength, diffuse scattering dominates. Calculate the ratio of irregularity height to wavelength to see which regime applies here.
Intuitive explanation
The key is comparing surface roughness to wavelength using the Rayleigh criterion for smooth vs. rough surfaces. When surface irregularities are much smaller than the incident wavelength, the surface appears optically smooth and reflects light specularly (like a mirror). When roughness approaches or exceeds the wavelength, diffuse scattering dominates. Calculate the ratio of irregularity height to wavelength to see which regime applies here.