Some laws of physics are hard to imagine without the use of visual aids. This does not apply to the usual light falling on various objects. So, at the boundary separating two media, there is a change in the direction of light rays if this boundary is much greater than the wavelength. In this case, the reflection of light occurs when part of its energy returns to the first medium. If part of the rays penetrates into another medium, then they are refracted. In physics, the flow of light energy that hits the boundary of two different media is called incident, and the one that returns from it to the first medium is called reflected. It is the mutual arrangement of these rays that determines the laws of reflection and refraction of light.
Terms
The angle between the incident beam and the perpendicular line to the interface between two media, restored to the point of incidence of the light energy flux, is called the angle of incidence. There is another important indicator. This is the angle of reflection. It occurs between the reflected beam and the perpendicular line restored to the point of its incidence. light canpropagate in a straight line only in a homogeneous medium. Different media absorb and reflect light radiation in different ways. The reflection coefficient is a value that characterizes the reflectivity of a substance. It shows how much energy brought by light radiation to the surface of the medium will be that which is carried away from it by reflected radiation. This coefficient depends on a number of factors, one of the most important being the angle of incidence and the composition of the radiation. Total reflection of light occurs when it falls on objects or substances with a reflective surface. So, for example, this happens when rays hit a thin film of silver and liquid mercury deposited on glass. Total reflection of light is quite common in practice.
Laws
The laws of reflection and refraction of light were formulated by Euclid in the 3rd century BC. BC e. All of them have been established experimentally and are easily confirmed by the purely geometric principle of Huygens. According to him, any point of the medium, to which the perturbation reaches, is a source of secondary waves.
The first law of light reflection: the incident and reflecting beams, as well as the perpendicular line to the interface between the media, restored at the point of incidence of the light beam, are located in the same plane. A plane wave falls on a reflective surface, the wave surfaces of which are stripes.
Another law says that the angle of reflection of light is equal to the angle of incidence. This is because they are mutually perpendicularsides. Based on the principles of equality of triangles, it follows that the angle of incidence is equal to the angle of reflection. It can be easily proved that they lie in the same plane with the perpendicular line restored to the interface between the media at the point of incidence of the beam. These most important laws are also valid for the reverse course of light. Due to the reversibility of energy, a beam propagating along the path of the reflected will be reflected along the path of the incident.
Properties of reflective bodies
The vast majority of objects only reflect the light radiation falling on them. However, they are not a source of light. Well-lit bodies are perfectly visible from all sides, since the radiation from their surface is reflected and scattered in different directions. This phenomenon is called diffuse (scattered) reflection. It occurs when light hits any rough surface. To determine the path of the beam reflected from the body at the point of its incidence, a plane is drawn that touches the surface. Then, in relation to it, the angles of incidence of rays and reflection are built.
Diffuse Reflection
Only due to the existence of diffuse (diffuse) reflection of light energy, we distinguish between objects that are not capable of emitting light. Any body will be absolutely invisible to us if the scattering of rays is zero.
Diffuse reflection of light energy does not cause discomfort in the eyes of a person. This is due to the fact that not all light returns to its original environment. So from the snowabout 85% of the radiation is reflected, from white paper - 75%, but from black velor - only 0.5%. When light is reflected from various rough surfaces, the rays are directed randomly with respect to each other. Depending on the extent to which surfaces reflect light rays, they are called matte or mirror. However, these terms are relative. The same surfaces can be specular and matte at different wavelengths of incident light. A surface that scatters rays evenly in different directions is considered absolutely matte. Although there are practically no such objects in nature, unglazed porcelain, snow, drawing paper are very close to them.
Mirror reflection
Specular reflection of light rays differs from other types in that when beams of energy fall on a smooth surface at a certain angle, they are reflected in one direction. This phenomenon is familiar to anyone who has ever used a mirror under the rays of light. In this case, it is a reflective surface. Other bodies also belong to this category. All optically smooth objects can be classified as mirror (reflective) surfaces if the sizes of inhomogeneities and irregularities on them are less than 1 micron (do not exceed the wavelength of light). For all such surfaces, the laws of light reflection are valid.
Reflection of light from different mirror surfaces
Mirrors with a curved reflective surface (spherical mirrors) are often used in technology. Such objects are bodiesshaped like a spherical segment. The parallelism of the rays in the case of reflection of light from such surfaces is strongly violated. There are two types of such mirrors:
• concave - reflect light from the inner surface of the segment of the sphere, they are called collecting, since parallel rays of light after reflection from them are collected at one point;
• convex - reflect light from the outer surface, while parallel rays are scattered to the sides, which is why convex mirrors are called scattering.
Options for reflecting light rays
A ray incident almost parallel to the surface touches it only a little, and then is reflected at a very obtuse angle. It then continues on a very low trajectory, as close as possible to the surface. A beam falling almost vertically is reflected at an acute angle. In this case, the direction of the already reflected beam will be close to the path of the incident beam, which is fully consistent with physical laws.
Refraction of light
Reflection is closely related to other phenomena of geometric optics, such as refraction and total internal reflection. Often, light passes through the boundary between two media. Refraction of light is a change in the direction of optical radiation. It occurs when it passes from one medium to another. The refraction of light has two patterns:
• the beam passing through the boundary between the media is located in a plane that passes through the perpendicular to the surface and the incident beam;
•angle of incidence and refraction are related.
Refraction is always accompanied by reflection of light. The sum of the energies of the reflected and refracted beams of rays is equal to the energy of the incident beam. Their relative intensity depends on the polarization of the light in the incident beam and the angle of incidence. The structure of many optical devices is based on the laws of light refraction.
