What is the angle of incidence and reflection. Law of Light Reflection

Electromagnetic nature of light. Speed of light. Geometric optics

Visible light is electromagnetic waves in the range from 3.8*10 -7 m to 7.6*10 -7 m. The speed of light c = 3*10 8 m/s. Huygens' principle. A wave front is a surface connecting all points of a wave that are in the same phase (that is, all points of a wave that are in the same state of oscillation at the same time). Each point to which the disturbance has reached itself becomes a source of secondary spherical waves. The wave surface is the envelope of secondary waves. For a spherical wave, the wave front is a sphere, the radius of which is R = vt, where v is the wave speed.

Geometric optics is a branch of optics that studies the laws of light propagation in transparent media and the reflection of light from mirror or translucent surfaces.

Laws of light reflection. 1. Incident ray, reflected ray and perpendicular, reconstructed y to the interface between the two media at the point of incidence of the beam, lie in the same plane.

The angle of reflection is equal to the angle of incidence.

REFRACTION OF LIGHT - a change in the direction of propagation of a light wave (light ray) when passing through the interface of two different transparent media. 1. The incident and refracted rays and the perpendicular drawn to the interface between the two media at the point of incidence of the ray lie in the same plane. 2. The ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant value for two media:,Where α - angle of incidence,β - refraction angle,n - a constant value independent of the angle of incidence.

– the relative refractive index of light in the second medium relative to the first. Shows how many times the speed of light in the first medium differs from the speed of light in the second

n - a physical quantity equal to the ratio of the speed of light in a vacuum to the speed of light in a given medium:

Absolute refractive index of the medium shows how many times the speed of light in a given medium is less than the speed of light in a vacuum. Total internal reflection is observed when a beam passes from an optically denser medium to an optically less dense one (from water to air). α0 is the limiting angle of total reflection, the angle of incidence at which the angle refraction is 90 0. Total internal reflection is used in light guides.

Some laws of physics are difficult 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, a change in the direction of light rays occurs if this boundary is much higher. Light occurs when part of its energy returns to the first medium. If some of the rays penetrate into another medium, then they are refracted. In physics, energy falling on the boundary of two different media is called incident, and energy that returns from it to the first medium is called reflected. It is the relative position 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 light energy flow, is called. There is another important indicator. This is the angle of reflection. It occurs between the reflected ray and the perpendicular line restored to the point of its incidence. Light can propagate in a straight line only in a homogeneous medium. Different media absorb and reflect light differently. Reflectance is a quantity that characterizes the reflectivity of a substance. It shows how much energy brought by light radiation to the surface of a medium will be that which is carried away from it by reflected radiation. This coefficient depends on a variety of factors, some of the most important being the angle of incidence and the composition of the radiation. Complete 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. Total reflection of light occurs quite often in practice.

Laws

The laws of reflection and refraction of light were formulated by Euclid back in the 3rd century. BC e. All of them were established experimentally and are easily confirmed by the purely geometric principle of Huygens. According to him, any point in the medium to which a disturbance reaches is a source of secondary waves.

First light: the incident and reflecting beam, as well as the perpendicular line to the interface, reconstructed at the point of incidence of the light beam, are located in the same plane. A plane wave is incident on a reflective surface, the wave surfaces of which are stripes.

Another law states that the angle of reflection of light is equal to the angle of incidence. This happens 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 proven 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 path of light. Due to the reversibility of energy, a ray propagating along the path of the reflected one will be reflected along the path of the incident one.

Properties of reflecting 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 (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 the angles of incidence of rays and reflection are constructed in relation to it.

Diffuse reflection

It is only due to the existence of scattered (diffuse) reflection of light energy that we distinguish 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 unpleasant sensations in the eyes. This occurs because not all the light returns to the original medium. So about 85% of the radiation is reflected from snow, 75% from white paper, and only 0.5% from black velor. When light is reflected from various rough surfaces, the rays are directed randomly in relation to each other. Depending on the extent to which surfaces reflect light rays, they are called matte or mirror. But still, these concepts are relative. The same surfaces can be mirrored or matte at different wavelengths of incident light. A surface that evenly scatters 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

Specular 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 anyone who has ever used a mirror under rays of light. In this case it is a reflective surface. Other bodies also fall into this category. All optically smooth objects can be classified as mirror (reflective) surfaces if the size of inhomogeneities and irregularities on them is less than 1 micron (does not exceed the wavelength of light). For all such surfaces, the laws of light reflection apply.

Reflection of light from different mirror surfaces

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

Concave - reflect light from the inner surface of a segment of a 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 beam incident almost parallel to the surface touches it only slightly, and then is reflected at a very obtuse angle. Then it continues along a very low trajectory, closest 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.

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 is the change in direction of optical radiation. It occurs when it passes from one environment 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;

The 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 incident beam and the angle of incidence. The design of many optical instruments is based on the laws of light refraction.

Dating back to around 300 BC. e.

Laws of reflection. Fresnel formulas

The law of light reflection - establishes a change in the direction of travel of a light ray as a result of a meeting with a reflecting (mirror) surface: the incident and reflected rays lie in the same plane with the normal to the reflecting surface at the point of incidence, and this normal divides the angle between the rays into two equal parts. The widely used but less precise formulation “angle of incidence equals angle of reflection” does not indicate the exact direction of reflection of the beam. However, it looks like this:

This law is a consequence of the application of Fermat's principle to a reflecting surface and, like all laws of geometric optics, is derived from wave optics. The law is valid not only for perfectly reflective surfaces, but also for the boundary of two media that partially reflects light. In this case, like the law of refraction of light, it does not state anything about the intensity of reflected light.

Reflection mechanism

When an electromagnetic wave hits a conducting surface, a current arises, the electromagnetic field of which tends to compensate for this effect, which leads to almost complete reflection of light.

Types of reflection

The reflection of light can be mirrored(that is, as observed when using mirrors) or diffuse(in this case, upon reflection, the path of the rays from the object is not preserved, but only the energy component of the light flux) depending on the nature of the surface.

Mirror O. s. distinguished by a certain relationship between the positions of the incident and reflected rays: 1) the reflected ray lies in the plane passing through the incident ray and the normal to the reflecting surface; 2) the angle of reflection is equal to the angle of incidence j. The intensity of reflected light (characterized by the reflection coefficient) depends on j and the polarization of the incident beam of rays (see Polarization of Light), as well as on the ratio of the refractive indices n2 and n1 of the 2nd and 1st media. This dependence (for a reflecting medium - a dielectric) is expressed quantitatively by the Fresnel formula. From them, in particular, it follows that when light is incident normal to the surface, the reflection coefficient does not depend on the polarization of the incident beam and is equal to

(n2 - n1)²/(n2 + n1)²

In the very important particular case of a normal fall from air or glass onto their interface (nair " 1.0; nst = 1.5) it is " 4%.

The nature of the polarization of reflected light changes with changes in j and is different for components of incident light polarized parallel (p-component) and perpendicular (s-component) to the plane of incidence. By plane of polarization we mean, as usual, the plane of oscillation of the electric vector of the light wave. At angles j equal to the so-called Brewster angle (see Brewster's law), the reflected light becomes completely polarized perpendicular to the plane of incidence (the p-component of the incident light is completely refracted into the reflecting medium; if this medium strongly absorbs light, then the refracted p-component passes into environment is a very small path). This feature of the mirror O. s. used in a number of polarizing devices. For j larger than the Brewster angle, the reflection coefficient from dielectrics increases with increasing j, tending to 1 in the limit, regardless of the polarization of the incident light. In a specular optical system, as is clear from Fresnel's formulas, the phase of reflected light in the general case changes abruptly. If j = 0 (light falls normally to the interface), then for n2 > n1 the phase of the reflected wave shifts by p, for n2< n1 - остаётся неизменной. Сдвиг фазы при О. с. в случае j ¹ 0 может быть различен для р- и s-составляющих падающего света в зависимости от того, больше или меньше j угла Брюстера, а также от соотношения n2 и n1. О. с. от поверхности оптически менее плотной среды (n2 < n1) при sin j ³ n2 / n1 является полным внутренним отражением, при котором вся энергия падающего пучка лучей возвращается в 1-ю среду. Зеркальное О. с. от поверхностей сильно отражающих сред (например, металлов) описывается формулами, подобными формулам Френеля, с тем (правда, весьма существенным) изменением, что n2 становится комплексной величиной, мнимая часть которой характеризует поглощение падающего света.

Absorption in a reflective medium leads to the absence of a Brewster angle and higher (compared to dielectrics) values of the reflection coefficient - even at normal incidence it can exceed 90% (this explains the widespread use of smooth metal and metallized surfaces in mirrors). The polarization characteristics also differ. light waves reflected from the absorbing medium (due to other phase shifts of the p- and s-components of the incident waves). The nature of the polarization of reflected light is so sensitive to the parameters of the reflecting medium that numerous optical methods for studying metals are based on this phenomenon (see Magneto-optics, Metal-optics).

Diffuse O. s. - its dispersion by the uneven surface of the 2nd medium in all possible directions. The spatial distribution of the reflected radiation flux and its intensity are different in different specific cases and are determined by the relationship between l and the size of the irregularities, the distribution of irregularities over the surface, lighting conditions, and the properties of the reflecting medium. The limiting case of spatial distribution of diffusely reflected light, which is not strictly fulfilled in nature, is described by Lambert’s law. Diffuse O. s. It is also observed from media whose internal structure is inhomogeneous, which leads to the scattering of light in the volume of the medium and the return of part of it to the first medium. Patterns of diffuse O. s. from such media are determined by the nature of the processes of single and multiple light scattering in them. Both absorption and scattering of light can exhibit a strong dependence on l. The result of this is a change in the spectral composition of diffusely reflected light, which (when illuminated with white light) is visually perceived as the color of bodies.

Total internal reflection

As the angle of incidence increases i, the angle of refraction also increases, while the intensity of the reflected beam increases, and the refracted beam decreases (their sum is equal to the intensity of the incident beam). At some value i = i k corner r= π / 2, the intensity of the refracted beam will become equal to zero, all the light will be reflected. With further increase in angle i > i k There will be no refracted ray; the light is completely reflected.

We will find the value of the critical angle of incidence at which total reflection begins, put it in the law of refraction r= π / 2, then sin r= 1 means:

sin i k = n 2 / n 1

Diffuse light scattering

θ i = θ r .
The angle of incidence is equal to the angle of reflection

Operating principle of a corner reflector

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See what “Reflection of light” is in other dictionaries:

The phenomenon that when light (optical radiation) falls from the first medium onto the interface with the second medium, the interaction of light with the second medium leads to the appearance of a light wave propagating from the interface back to the first... ... Physical encyclopedia

The return of a light wave when it is incident on the interface between two media with different refractive indices back into the first medium. There are specular reflections of light (the dimensions l of irregularities on the interface are less than the length of the light... ... Big Encyclopedic Dictionary

REFLECTION OF LIGHT, the return of part of the light beam incident on the interface between two media back to the first medium. A distinction is made between specular reflection of light (the dimensions L of irregularities on the interface are less than the light wavelength l) and diffuse reflection (L?... ... Modern encyclopedia

Reflection of light- REFLECTION OF LIGHT, the return of part of the light beam incident on the interface between two media “back” to the first medium. A distinction is made between specular reflection of light (the dimensions L of irregularities on the interface are less than the light wavelength l) and diffuse reflection (L... Illustrated Encyclopedic Dictionary

light reflection- The phenomenon that light incident on the interface between two media with different refractive indices is partially or completely returned to the medium from which it falls. [Collection of recommended terms. Issue 79. Physical... ... Technical Translator's Guide

The phenomenon that when light (optical radiation (See Optical radiation)) falls from one medium onto its interface with the 2nd medium, the interaction of light with matter leads to the appearance of a light wave,... ... Great Soviet Encyclopedia

The return of a light wave when it falls on the interface between two media with different refractive indices “back” to the first medium. There are specular reflections of light (the dimensions l of irregularities on the interface are less than the length of the light... ... encyclopedic Dictionary

light reflection- šviesos atspindys statusas T sritis fizika atitikmenys: engl. light reflection vok. Reflexion des Lichtes, f rus. reflection of light, n pranc. réflexion de la lumière, f… Fizikos terminų žodynas

light reflection- ▲ reflection (from which) light reflection. shine. albedo. albedometer. ↓ reflector. reflectometer. metal optics... Ideographic Dictionary of the Russian Language

The return of a light wave when it falls on the interface between two different media. refractive indices back to the first medium. If the roughness of the interface surface is small compared to the wavelength X of the incident light, then a specular O. with ... Big Encyclopedic Polytechnic Dictionary

Books

Total internal reflection of light. Educational research, Mayer Valery Vilhelmovich, The book contains descriptions of educational experimental studies of the phenomenon of total internal reflection from the boundary of optically homogeneous and layered inhomogeneous media. Simple physical... Category: Textbooks for schoolchildren Series: Library of teachers and students Publisher: FIZMATLIT, Manufacturer:

Geometric optics is a branch of optics that studies the laws of light propagation in transparent media and the reflection of light from mirror or translucent surfaces. The basic laws of geometric optics are listed below:

Law of rectilinear propagation of light.

In an optically homogeneous medium (in particular, in a vacuum), light rays propagate rectilinearly. The straightness of the propagation of light explains the formation of a shadow, i.e. areas where light energy does not reach. When the size of the source (luminous point) is small, a sharply defined shadow is obtained.

When the source size is large, blurred shadows are created.

The fact is that from each point of the source light propagates in a straight line and an object illuminated by two luminous points will give two divergent shadows, the overlap of which forms a shadow of uneven density. A complete shadow with an extended source is formed only in those areas of the screen where the light does not reach at all. Along the edges of the full shadow is a lighter area. This is partial shade.

Law of independence of light beams.

The energy in each beam propagates independently of other beams; The illumination of the surface on which several beams fall is equal to the sum of the illumination created by each beam separately.

Law of light reflection.

A ray of light in a homogeneous medium is rectilinear until it reaches the boundary of this medium with another medium. At the boundary of two media, the beam changes its direction. Some of the light (and in some cases all of the light) returns to the first medium. This phenomenon is called reflection of light. At the same time, the light partially passes into the second medium, while changing the direction of its propagation - refracted.

Specular and diffuse reflection.

Depending on the properties of the interface between the two media, reflection may have a different character. If the boundary has the form of a surface whose irregularities are smaller than the wavelength of light, then it is called mirror. Rays of light falling on such a surface in a narrow parallel beam also travel in similar directions after reflection. This directional reflection is called mirrored. If the size of the irregularities is greater than the wavelength of light, then the narrow beam is scattered at the boundary. After reflection, light rays travel in all possible directions. This reflection is called absent-minded or diffuse. It is thanks to diffuse reflection of light that we can see objects that do not themselves emit light. To a small extent, light scattering occurs when it is reflected even from the smoothest surface, for example, from an ordinary mirror. Otherwise we would not be able to see the surface of the mirror.

Law of light reflection.

The law of light reflection determines the relative position of the incident ray, the reflected ray and the perpendicular to the surface reconstructed at the point of incidence.

This law is valid for waves of any nature and is formulated as follows: the incident ray, the reflected ray and the perpendicular to the interface between the two media, restored at the point of incidence of the ray, lie in the same plane; the angle of reflection  is equal to the angle of incidence It is obvious that this law will also be true if the light propagates in the opposite direction. Reversibility The path of light rays is their important property.

Image in a plane mirror.

Let the luminous point be in front of a flat light-reflecting surface, i.e. flat mirror. Let's ask the question: where will we see image this point if we look in the mirror? To answer this question, consider several rays emanating from point S and

It seems to a person that the rays come out from point S1, which can be found by continuing the rays in the opposite direction until they intersect. Point S1 will therefore be an image of point S in a plane mirror. This image is called imaginary, since at point S1 it is not the reflected rays themselves that intersect, but their continuations. Light energy does not reach this point. Let us consider any two rays of a diverging beam, for example, the outer rays of the beam entering the eye - rays AB and CD. In triangles SAC and S1AC, side AC is common. Using the law of reflection, one can prove that the angles in triangles adjacent to this side are correspondingly congruent. Therefore, the triangles are congruent and will align with each other if the pattern is folded along the mirror line. This means that point S1 is located symmetrically to point S relative to the mirror. Therefore, to find the image of a point, it is enough to lower a perpendicular from it onto the mirror or its extension and extend it to the same distance behind the mirror.

The law of light refraction.

At the boundary of two media, light changes the direction of its propagation. Part of the light energy returns to the first medium, i.e. is happening light reflection. If the second medium is transparent, then part of the light, under certain conditions, can pass through the boundary of the media, also changing, as a rule, the direction of its propagation. This phenomenon is called refraction of light. Due to refraction, an apparent change in the size, shape and location of objects is observed. Simple observations can convince us of this. Place the pencil at an angle in a glass of water. The part of the pencil that is in the water seems to be shifted to the side and increased in diameter.

Such phenomena are explained by changes in the direction of rays at the boundary of two media. A ray propagating in the first medium and reaching the boundary is called incident ray. It makes an angle  with the perpendicular to the boundary drawn through the point of incidence, called angle of incidence. The ray passing through the second Wednesday is called refracted ray. The angle  that this ray forms with the same perpendicular is called refraction angle.

The law of refraction, established experimentally in the 17th century, is formulated as follows: The incident ray, the refracted ray and the perpendicular to the interface between the two media, restored at the point of incidence of the ray, lie in the same plane; the ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant value for two given media.

Sin a / sin b = n

Refractive index.

The constant value included in the law of refraction of light is called relative refractive index or the refractive index of one medium relative to the first. The refractive index of a medium relative to vacuum is called absolute refractive index this environment. It is equal to the sine ratio angle of incidence to sine refraction angle when a light beam passes from a vacuum into a given medium. The relative refractive index n is related to the absolute indices n2 and n1 of the first medium by the relation:

Therefore, the law of refraction can be written as follows:

Sina/sinb=n2 /n1 A medium with a lower absolute refractive index is usually called optically less dense medium The absolute refractive index of a medium has a deep physical meaning. It is related to the speed of light propagation in a given medium and depends on the physical state of the medium in which the light propagates, i.e. on the temperature, density of the substance, and the presence of elastic tension in it. The refractive index also depends on the characteristics of the light itself. For red light it is less than for green, and for green it is less than for violet.

Total internal reflection.

If n - refractive index glass relative to air (n>1), then the refractive index of air relative to glass will be equal to 1/n. In this case, glass is the first medium, and air is the second. The law of refraction will be written as follows:

sin / sin= 1/nIn this case refraction angle more angle of incidence, because sin= n*sin, and n>1; therefore, sin> sinand therefore, the angle of refraction is greater than the angle of incidence (>). So, moving to optically less dense medium, the beam deviates away from the perpendicular to the boundary of the two media. The largest possible angle of refraction  = 90 corresponds to the angle of incidence 0. At an angle of incidence >0, the refracted beam will disappear, and all light is reflected from the interface, i.e. is happening total reflection of light.

The law of reflection was first mentioned in Euclid's Catoptrics, dating from around 300 BC. e.

Laws of reflection. Fresnel formulas

Reflection mechanism

When an electromagnetic wave hits a conducting surface, a current arises, the electromagnetic field of which tends to compensate for this effect, which leads to almost complete reflection of light.

Types of reflection

(n2 - n1)²/(n2 + n1)²

In the very important particular case of a normal fall from air or glass onto their interface (nair " 1.0; nst = 1.5) it is " 4%.

Total internal reflection

We will find the value of the critical angle of incidence at which total reflection begins, put it in the law of refraction r= π / 2, then sin r= 1 means:

sin i k = n 2 / n 1

Diffuse light scattering

θ i = θ r .
The angle of incidence is equal to the angle of reflection

Operating principle of a corner reflector

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See what the “Law of Light Reflection” is in other dictionaries:

law of light reflection- šviesos atspindžio dėsnis statusas T sritis fizika atitikmenys: engl. light reflexion law vok. Reflexionsgesetz des Lichtes, n rus. law of light reflection, m pranc. loi de réflexion de la lumière, f … Fizikos terminų žodynas

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