Reflection of light. The law of light reflection. Full reflection of light

Some laws of physics are difficult to imagine without the use of visual aids. This does not apply to the light familiar to all, falling on various objects. So on the boundary separating the two media, there is a change in the direction of the light rays in the event that this boundary is much longer than the wavelength. At the same time, light reflection occurs when a part of its energy is returned to the first medium. If a part of the rays penetrates into another medium, then their refraction occurs. In physics, the flux of light energy falling on the boundary of two different media is called falling, 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.

The 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 light energy flux is called the angle of incidence. There is another important indicator. This is the angle of reflection. It arises between the reflected ray and the perpendicular line, restored to the point of its fall. Light can propagate rectilinearly only in a homogeneous medium. Different media absorb and reflect the radiation of light differently. The reflection coefficient is a quantity characterizing the reflectivity of a substance. It shows how much energy produced by light radiation on the surface of the medium is the one that will be carried away from it by reflected radiation. This coefficient depends on a variety of factors, one of the most important are 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 the rays hit a thin film of silver and liquid mercury deposited on the glass. Full reflection of light in practice occurs quite often.

Laws

The laws of reflection and refraction of light were formulated by Euclid in the third century. BC. E. All of them have been established experimentally and are easily confirmed by the purely geometric principle of Huygens. According to it, 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 beam, as well as the perpendicular line to the media interface, reconstructed at the point of incidence of the light beam, are located in the same plane. A plane wave is incident on the reflecting surface, whose wave surfaces are strips.

Another law says that the angle of light reflection is equal to the angle of incidence. This is because they have mutually perpendicular sides. Proceeding from the principles of equality of triangles, it follows that the angle of incidence is equal to the angle of reflection. One can easily prove that they lie in the same plane with a perpendicular line, restored to the interface of the media at the point of incidence of the ray. 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 beam will be reflected along the path of the incident beam.

Properties of reflecting bodies

The overwhelming majority of objects only reflect the light radiation incident on them. They are not a source of light. Well-lit bodies are perfectly visible from all directions, as 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 surfaces. To determine the path of the ray reflected from the body at the point of its fall, a plane is made to touch the surface. Then, with respect to it, the angles of incidence of rays and reflection are plotted.

Diffuse reflection

Only due to the existence of scattered (diffuse) reflection of light energy, we distinguish objects that can not emit light. Any body will be completely invisible to us if the scattering of rays is zero.

Diffuse reflection of light energy does not cause unpleasant sensations in the eyes of a person. This is due to the fact that not all light is returned to the original environment. So from the snow reflects about 85% of the radiation, from white paper - 75%, well, from the velor of black color - only 0.5%. When light is reflected from various rough surfaces, the rays are randomly directed towards each other. Depending on the degree to which the surface is reflected by light rays, they are called opaque or specular. But still these concepts are relative. The same surfaces can be specular and opaque at different wavelengths of incident light. The surface, which evenly disperses the rays 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

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 belong to this category. All optically smooth objects can be referred to mirror (reflecting) surfaces if the dimensions of inhomogeneities and irregularities on them are less than 1 μm (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

In technology, mirrors with a curved reflecting surface (spherical mirrors) are often used. Such objects are bodies in the form of a spherical segment. The parallelism of the rays in the case of the reflection of light from such surfaces is strongly violated. There are two types of such mirrors:

• concave - reflect light from the inner surface of a segment of a sphere, they are called collectors, because parallel rays of light after reflection from them collect 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.

Variants of reflection of light rays

The beam, which falls almost parallel to the surface, only touches it a little, and then reflects at a very blunt angle. Then he continues his journey along a very low trajectory, maximally located to the surface. The beam, which falls almost vertically, is reflected at an acute angle. In this case, the direction of the already reflected ray will be close to the path of the incident ray, which fully corresponds to the physical laws.

Light refraction

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 refers to the change in the direction of optical radiation. It occurs when it passes from one environment to another. Refraction of light has two regularities:

• a ray passing through the boundary between media is located in a plane that passes through a perpendicular to the surface and a falling beam;

• angle of incidence and refraction are related.

Refraction is always accompanied by a 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 laws of light refraction are based on the arrangement of many optical instruments.