A photographer sets up two reflectors to bounce light from a camera-flash onto a subject. Reflector 1 is a sheet of highly polished aluminum whose surface irregularities are on the order of 0.01μm. Reflector 2 is a crumpled sheet of household aluminum foil that has been opened out again; its surface has hills and valleys with typical lateral dimensions of 0.5mm and height variations of 0.1mm. The flash emits white light with wavelengths clustered around 550nm. Students notice that the polished sheet directs a well-defined bright patch onto the subject, whereas the foil produces a broad, soft illumination filling much of the room.
(a) For each reflector, identify whether the ray model alone is sufficient to predict the observed illumination pattern. Justify your choices in terms of relevant physical length scales.
(b) Using appropriate physical reasoning, explain why the polished sheet produces specular reflection while the crumpled foil leads to diffuse reflection, even though both are made of the same material.
(c) Predict qualitatively how replacing the camera-flash with a green laser pointer (wavelength 532nm, beam diameter 2mm) would change the appearance of the reflection from the crumpled foil. State which model (ray or wave) you would rely on for this prediction and defend your choice.