How does Corpuscular Theory and Wave Theory of Light affects the characteristics of light such as reflection from a smooth surface and diffraction.What theory is the best and why?
In terms of reflection off a smooth surface, the corpuscular thory makes more sense. Sir Isaac Newton thought light was composed of tiny particles, called "corpuscles", which traveled in a direct path, each one having a constant velocity. And isn't that what happens when light is reflected off a smooth surface, all those little particles simply "bounce" off the surface as they contact it? Newton's theory explained a lot of things about light, such as the photoelectric effect.
But it didn't explain them all satisfactorily. After about one hundred years, Newton's theory was first rejected in favor of Huygen's wave theory of light, then tenets of both were incorporated to form the particle-wave theory of light. Diffraction was one of the things Newton's theory would not satisfy. Diffraction is the ability of waves to bend around obstructions or openings. Waves, particularly longer waves, bend very easily, which is what diffraction is.