Some laws of physics are difficult to imagine without the use of visual aids. This does not apply to the light that is familiar to everyone, falling on various objects. So at the border separating the two media, there is a change in the direction of light rays in the event that this border is much longer 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 enters the boundary of two different media is called incident, and the one that returns from it to the first medium is 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 the two media, restored to the point of incidence of the flux of light energy, 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 can propagate rectilinearly exclusively in a homogeneous environment. Different media absorb and reflect light in different ways. 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 variety of factors, one of the most important is the angle of incidence and the composition of the radiation. Full reflection of light occurs when it falls on objects or substances with a reflective surface. For example, this happens when rays hit a thin film of silver and liquid mercury deposited on glass. Full reflection of light in practice is quite common.
The laws
The laws of reflection and refraction of light were formulated by Euclid in the 3rd century. BC e. All of them were established experimentally and are easily confirmed by the purely geometric Huygens principle. According to it, any point of the medium to which the disturbance reaches is a source of secondary waves.
The first law of reflection of light: the incident and reflective beam, as well as the perpendicular line to the interface, restored at the point of incidence of the light beam, are located in the same plane. A plane wave is incident on the reflective surface, the wave surfaces of which are strips.
Another law states that the angle of reflection of light is equal to the angle of incidence. This is because they have mutually perpendicular sides. 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 at the point of incidence of the beam. These most important laws are also valid for the reverse passage 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 incident on them. However, they are not a source of light. Well-lit bodies are clearly visible from all sides, since radiation from their surface is reflected and scattered in different directions. This phenomenon is called diffuse (diffuse) reflection. It occurs when light hits any rough surfaces. To determine the path of the beam reflected from the body at the point of incidence, a plane is drawn touching the surface. Then, in relation to it, 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 objects that are not able to emit 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, about 85% of radiation is reflected from snow, from 75% from white paper, and only 0.5% from black velor. When light is reflected from various rough surfaces, the rays are randomly directed towards each other. Depending on the degree to which surfaces reflect light rays, they are called matte or mirror. But still, these concepts are relative. The same surfaces can be mirrored and matte at different wavelengths of the incident light. A surface that evenly scatters the rays in different directions is considered completely matte. Although there are practically no such objects in nature, unglazed porcelain, snow, and drawing paper are very close to them.
Mirror reflection
Mirror reflection of light rays differs from other types in that when energy beams fall on a smooth surface at a certain angle, they are reflected in one direction. This phenomenon is familiar to everyone who once used a mirror under the rays of light. In this case, it is a reflective surface. Other bodies also belong to this category. Mirror (reflective) surfaces can include all optically smooth objects if the dimensions of the inhomogeneities and irregularities on them are less than 1 μm (do not exceed the value of the wavelength of light). For all such surfaces, the laws of light reflection are valid.
Reflection of light from different mirror surfaces
In technology, mirrors with a curved reflective surface (spherical mirrors) are often used. Such objects are bodies in the shape of a spherical segment. The parallelism of the rays in the case of reflection of light from such surfaces is greatly disrupted. There are two types of mirrors:
• concave - reflect light from the inner surface of a segment of a sphere, they are called collecting, because 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 mirrors.
Light reflection options
A ray incident almost parallel to the surface only touches it a little, and then it is reflected at a very obtuse angle. Then he continues the path along a very low path, maximally located 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 called a change in the direction of optical radiation. It occurs when it passes from one medium to another. Refraction of light has two laws:
• 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 ray. Their relative intensity depends on the polarization of light in the incident beam and the angle of incidence. The device of many optical devices is based on the laws of light refraction.