In order to better understand which model is used to understand the reflection and refraction of light, we must go back a little in history. Although Galileo and Isaac Newton, based on mechanics, were able to explain both simple and complex motions (as, by example, the movement of the planets), several scientists, at the end of the 19th century, wanted to explain the physical phenomena based on only one theory.
THE kinetic-molecular theory, based on the conservation of momentum, a concept in mechanics, interpreted microscopic phenomena related to the movement of molecules. Therefore, it was thought that facts related to light could be explained by a theoretical model based on mechanics.
Based on these principles, Newton presented the model corpuscular of light. The model proposed by Newton was quite satisfactory, as it was able to satisfactorily explain the luminous phenomena that until then were known only to scientists.
Newton's model considered that light was composed of particles (or corpuscles) that emerged from the light source. His model also considered that the propagation of light was straight due to the fact that the particles that make up light have a very small mass and because they propagate quickly.
The principle of independence of light rays was well explained by the corpuscular model of light. Considering the existence of light corpuscles, two light rays intersect because it is difficult for particles in one beam to collide with particles in the other beam.
The corpuscular model of light also explains the diffuse reflection of light model. when the particles that make up light collide with a surface, they obey the laws of reflection. However, as the surface is irregular, the reflected particles propagate in different directions, justifying why the reflection is diffuse.
On an opaque or dark collecting surface, the light particles are neither reflected nor transmitted, they are absorbed by the collector, heating it. In this case, the light particles, when colliding with the unpolished surface of the collector plate, transfer energy to the molecules of the plate. That's why materials that reflect light well practically do not heat up when they receive a beam of light.
The corpuscular model also explains the refraction of light. According to Newton, the change in the direction of light propagation, or rather, of light corpuscles, was due to the existence of forces. In reflection, the corpuscles were repelled by a repulsive force coming from the reflecting surface. In refraction, these corpuscles were attracted into the other medium. Thus, if the direction of incidence were oblique, the action of the attractive force applied by the medium on the light corpuscles would change its propagation direction.
By Domitiano Marques
Graduated in Physics
Source: Brazil School - https://brasilescola.uol.com.br/fisica/luz-como-particula.htm
