Lesson summary "Reflection of light. The law of light reflection"

Light is an important component of our life. Without it, life on our planet is impossible. At the same time, many phenomena that are associated with light are today actively used in various areas of human activity, ranging from the production of electrical devices to spacecraft. One of the fundamental phenomena in physics is the reflection of light.

Reflection of light

The law of light reflection is studied at school. Our article can tell you what you should know about it, as well as a lot of other useful information.

Basic knowledge about light

As a rule, physical axioms are among the most understandable because they have visual manifestations that can be easily observed at home. The law of light reflection implies a situation where light rays change direction when they collide with various surfaces.

Note! The refractive boundary significantly increases a parameter such as wavelength.

During the refraction of the rays, part of their energy will return back to the primary medium. When some of the rays penetrate into another medium, their refraction is observed.
To understand all these physical phenomena, you need to know the appropriate terminology:

• the flow of light energy in physics is defined as incident when it hits the interface between two substances;
• part of the light energy that in a given situation returns to the primary medium is called reflected;

Note! There are several formulations of the reflection rule. No matter how you formulate it, it will still describe the relative position of reflected and incident rays.

• angle of incidence. Here we mean the angle that is formed between the perpendicular line of the boundary of the media and the light incident on it. It is determined at the point of incidence of the beam;

Beam angles

• reflection angle. It is formed between the reflected ray and the perpendicular line that was reconstructed at the point of its incidence.

In addition, you need to know that light can propagate exclusively rectilinearly in a homogeneous medium.

Note! Different media may reflect and absorb light differently.

This is where the reflectance comes from. This is a quantity that characterizes the reflectivity of objects and substances. It means how much radiation brought by the light flux to the surface of the medium will amount to the energy that will be reflected from it. This coefficient depends on a number of factors, among which the composition of the radiation and the angle of incidence are of greatest importance.
Complete reflection of the light flux is observed when the beam falls on substances and objects with a reflective surface. For example, the reflection of a beam can be observed when it hits glass, liquid mercury or silver.

A short historical excursion

The laws of refraction and reflection of light were formed and systematized back in the 3rd century. BC e. They were developed by Euclid.

All laws (refraction and reflection) that relate to this physical phenomenon were established experimentally and can easily be confirmed by Huygens' geometric principle. According to this principle, any point in the medium that a disturbance can reach acts as a source of secondary waves.
Let's look at the laws that exist today in more detail.

Laws are the basis of everything

The law of reflection of light flux is defined as a physical phenomenon during which light sent from one medium to another will be partially returned back at their separation.

Reflection of light at the interface

The human visual analyzer observes light at the moment when the beam coming from its source hits the eyeball. In a situation where the body does not act as a source, the visual analyzer can perceive rays from another source that are reflected from the body. In this case, light radiation incident on the surface of an object can change the direction of its further propagation. As a result, the body that reflects the light will act as its source. When reflected, part of the flow will return to the first medium from which it was originally directed. Here the body that will reflect it will become the source of the already reflected flow.
There are several laws for this physical phenomenon:

• the first law states: the reflecting and incident beam, together with the perpendicular line that appears at the interface between the media, as well as at the reconstructed point of incidence of the light flux, must be located in the same plane;

Note! Here it is implied that a plane wave falls on the reflective surface of an object or substance. Its wave surfaces are stripes.

First and second laws

• second law. Its formulation is as follows: the angle of reflection of the light flux will be equal to the angle of incidence. This is due to the fact that they have mutually perpendicular sides. Taking into account the principles of equality of triangles, it becomes clear where this equality comes from. Using these principles, one can easily prove that these angles are in the same plane with the drawn perpendicular line, which was restored at the boundary of separation of two substances at the point of incidence of the light beam.

These two laws in optical physics are basic. Moreover, they are also valid for a beam that has a reverse path. As a result of the reversibility of the beam energy, the flow propagating along the path of the previously reflected one will be reflected similarly to the path of the incident one.

The Law of Reflection in Practice

The implementation of this law can be verified in practice. To do this, you need to direct a thin beam at any reflective surface. A laser pointer and a regular mirror are perfect for these purposes.

The effect of the law in practice

Point the laser pointer at the mirror. As a result, the laser beam will be reflected from the mirror and spread further in a given direction. In this case, the angles of the incident and reflected beam will be equal even when looking at them normally.

Note! Light from such surfaces will be reflected at an obtuse angle and further propagate along a low trajectory, which is located quite close to the surface. But the beam, which will fall almost vertically, will be reflected at an acute angle. At the same time, its further path will be almost identical to the falling one.

As you can see, the key point of this rule is the fact that the angles must be measured from the perpendicular to the surface at the point of incidence of the light flux.

Note! This law is subject to not only light, but also any types of electromagnetic waves (microwave, radio, x-ray waves, etc.).

Features of diffuse reflection

Many objects can only reflect light radiation incident on their surface. Well-lit objects are clearly visible from different angles, as their surface reflects and scatters light in different directions.

Diffuse reflection

This phenomenon is called scattered (diffuse) reflection. This phenomenon occurs when radiation hits various rough surfaces. Thanks to it, we are able to distinguish objects that do not have the ability to emit light. If the scattering of light radiation is zero, then we will not be able to see these objects.

Note! Diffuse reflection does not cause discomfort to a person.

The absence of discomfort is explained by the fact that not all the light, according to the rule described above, returns to the primary environment. Moreover, this parameter will be different for different surfaces:

• snow reflects approximately 85% of the radiation;
• for white paper - 75%;
• for black and velor - 0.5%.

If the reflection comes from rough surfaces, then the light will be directed randomly in relation to each other.

Features of Mirroring

Specular reflection of light radiation differs from previously described situations. This is due to the fact that as a result of the flow falling on a smooth surface at a certain angle, they will be reflected in one direction.

Mirror reflection

This phenomenon can be easily reproduced using a regular mirror. When the mirror is directed towards the sun's rays, it will act as an excellent reflective surface.

Note! A number of bodies can be classified as mirror surfaces. For example, this group includes all smooth optical objects. But such a parameter as the size of irregularities and inhomogeneities in these objects will be less than 1 micron. The wavelength of light is approximately 1 micron.

All such specular reflective surfaces obey the previously described laws.

Use of law in technology

Today, technology often uses mirrors or mirrored objects that have a curved reflective surface. These are so-called spherical mirrors.
Such objects are bodies that have the shape of a spherical segment. Such surfaces are characterized by a violation of the parallelism of the rays.
There are currently two types of spherical mirrors:

• concave. They are capable of reflecting light radiation from the inner surface of their sphere segment. When reflected, the rays are collected here at one point. Therefore, they are often also called “gatherers”;

Concave mirror

• convex. Such mirrors are characterized by reflection of radiation from the outer surface. During this, dispersion occurs to the sides. For this reason, such objects are called “scattering”.

Convex mirror

In this case, there are several options for the behavior of the rays:

• burning almost parallel to the surface. In this situation, it only slightly touches the surface and is reflected at a very obtuse angle. Then it follows a fairly low trajectory;
• when falling back, the rays are reflected at an acute angle. In this case, as we said above, the reflected beam will follow a path very close to the incident one.

As we see, the law is fulfilled in all cases.

Conclusion

The laws of reflection of light radiation are very important to us because they are fundamental physical phenomena. They have found extensive application in various fields of human activity. The basics of optics are taught in high school, which once again proves the importance of such basic knowledge.

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Laws of reflection and refraction of light. Total internal reflection of light

The laws of light reflection were discovered experimentally in the 3rd century BC by the ancient Greek scientist Euclid. Also, these laws can be obtained as a consequence of Huygens’ principle, according to which every point in the medium to which a disturbance has reached is a source of secondary waves. The wave surface (wave front) at the next moment is a tangent surface to all secondary waves. Huygens' principle is purely geometric.

A plane wave falls on the smooth reflective surface of a CM (Fig. 1), that is, a wave whose wave surfaces are stripes.

Rice. 1 Huygens' construction.

A 1 A and B 1 B are the rays of the incident wave, AC is the wave surface of this wave (or the wave front).

Bye wave front from point C will move in time t to point B, from point A a secondary wave will spread across the hemisphere to a distance AD ​​= CB, since AD ​​= vt and CB = vt, where v is the speed of wave propagation.

The wave surface of the reflected wave is a straight line BD, tangent to the hemispheres. Further, the wave surface will move parallel to itself in the direction of the reflected rays AA 2 and BB 2.

Right triangles ΔACB and ΔADB have a common hypotenuse AB and equal legs AD = CB. Therefore they are equal.

Angles CAB = α and DBA = γ are equal because they are angles with mutually perpendicular sides. And from the equality of triangles it follows that α = γ.

From Huygens' construction it also follows that the incident and reflected rays lie in the same plane with the perpendicular to the surface restored at the point of incidence of the ray.

The laws of reflection are valid when light rays travel in the opposite direction. Due to the reversibility of the path of light rays, we have that a ray propagating along the path of the reflected one is reflected along the path of the incident one.

Most bodies only reflect the radiation incident on them, without being a source of light. Illuminated objects are visible from all sides, since light is reflected from their surface in different directions, scattering.

This phenomenon is called diffuse reflection or diffuse reflection. Diffuse reflection of light (Fig. 2.) occurs from all rough surfaces. To determine the path of the reflected ray of such a surface, a plane tangent to the surface is drawn at the point of incidence of the ray, and the angles of incidence and reflection are constructed in relation to this plane.

Rice. 2. Diffuse reflection of light.

For example, 85% of white light is reflected from the surface of snow, 75% from white paper, 0.5% from black velvet. Diffuse reflection of light does not cause unpleasant sensations in the human eye, unlike specular reflection.

Specular reflection of light– this is when light rays falling on a smooth surface at a certain angle are reflected predominantly in one direction (Fig. 3.). The reflective surface in this case is called mirror(or mirror surface). Mirror surfaces can be considered optically smooth if the size of irregularities and inhomogeneities on them does not exceed the light wavelength (less than 1 micron). For such surfaces, the law of light reflection is satisfied.

Rice. 3. Specular reflection of light.

Flat mirror is a mirror whose reflecting surface is a plane. A flat mirror makes it possible to see objects in front of it, and these objects appear to be located behind the mirror plane. In geometric optics, each point of the light source S is considered the center of a diverging beam of rays (Fig. 4.). Such a beam of rays is called homocentric. The image of point S in an optical device is the center S’ of a homocentric reflected and refracted beam of rays in various media. If light scattered by the surfaces of various bodies falls on a flat mirror, and then, reflected from it, falls into the eye of the observer, then images of these bodies are visible in the mirror.

Rice. 4. Image created using a plane mirror.

The image S’ is called real if the reflected (refracted) rays of the beam intersect at point S 1. The image S 1 is called imaginary if it is not the reflected (refracted) rays themselves that intersect in it, but their continuations. Light energy does not reach this point. In Fig. Figure 4 shows an image of a luminous point S, which appears using a flat mirror.

Beam SO falls on the CM mirror at an angle of 0°, therefore, the angle of reflection is 0°, and this ray, after reflection, follows the path OS. From the entire set of rays falling from point S onto a flat mirror, we select the ray SO 1.

The SO 1 beam falls on the mirror at an angle α and is reflected at an angle γ (α = γ). If we continue the reflected rays behind the mirror, they will converge at point S 1, which is a virtual image of point S in a plane mirror. Thus, it seems to a person that the rays are coming out of point S 1, although in fact there are no rays leaving this point and entering the eye. The image of point S 1 is located symmetrically to the most luminous point S relative to the CM mirror. Let's prove it.

Beam SB incident on the mirror at an angle of 2 (Fig. 5.), according to the law of light reflection, is reflected at an angle of 1 = 2.

Rice. 5. Reflection from a flat mirror.

From Fig. 1.8 you can see that angles 1 and 5 are equal – like vertical ones. The sums of the angles are 2 + 3 = 5 + 4 = 90°. Therefore, angles 3 = 4 and 2 = 5.

Right triangles ΔSOB and ΔS 1 OB have a common leg OB and equal acute angles 3 and 4, therefore, these triangles are equal in side and two angles adjacent to the leg. This means that SO = OS 1, that is, point S 1 is located symmetrically to point S relative to the mirror.

In order to find the image of an object AB in a flat mirror, it is enough to lower perpendiculars from the extreme points of the object onto the mirror and, continuing them beyond the mirror, set aside a distance behind it equal to the distance from the mirror to the extreme point of the object (Fig. 6.). This image will be virtual and life-size. The dimensions and relative position of the objects are preserved, but at the same time, in the mirror, the left and right sides of the image change places compared to the object itself. The parallelism of light rays incident on a flat mirror after reflection is also not violated.

Rice. 6. Image of an object in a flat mirror.

In technology, mirrors with a complex curved reflecting surface, for example, spherical mirrors, are often used. Spherical mirror- this is the surface of the body, having the shape of a spherical segment and specularly reflecting light. The parallelism of rays when reflected from such surfaces is violated. The mirror is called concave, if the rays are reflected from the inner surface of the spherical segment.

Parallel light rays, after reflection from such a surface, are collected at one point, which is why a concave mirror is called collecting. If the rays are reflected from the outer surface of the mirror, then it will convex. Parallel light rays are scattered in different directions, so convex mirror called dispersive.

Refraction At the interface between two media, the incident light flux is divided into two parts: one part is reflected, the other is refracted.
V. Snell (Snellius) before H. Huygens and I. Newton in 1621 experimentally discovered the law of refraction of light, but did not receive a formula, but expressed it in the form of tables, because By this time, the functions sin and cos were not yet known in mathematics.
The refraction of light obeys the law: 1. The incident beam and the refracted beam lie in the same plane with the perpendicular established at the point of incidence of the beam to the interface between the two media. 2. The ratio of the sine of the angle of incidence to the sine of the angle of refraction for two given media is a constant value (for monochromatic light).
The reason for refraction is the difference in the speed of propagation of waves in different media.
The value equal to the ratio of the speed of light in a vacuum to the speed of light in a given medium is called the absolute refractive index of the medium. This tabular value is a characteristic of a given environment.
The value equal to the ratio of the speed of light in one medium to the speed of light in another is called the relative refractive index of the second medium relative to the first.
Proof of the law of refraction. Propagation of incident and refracted rays: MM" - the interface between two media. Rays A 1 A and B 1 B - incident rays; α - angle of incidence; AC - wave surface at the moment when ray A 1 A reaches the interface between the media. Using Using Huygens' principle, we will construct a wave surface at the moment when ray B 1 B reaches the interface between the media. We will construct refracted rays AA 2 and BB 2. β is the angle of refraction. AB is the common side of triangles ABC and ABD. Since the rays and wave surfaces are mutual are perpendicular, then angle ABD= α and angle BAC=β. Then we get:
In a prism or plane-parallel plate, refraction occurs on each face in accordance with the law of light refraction. Don't forget that there is always a reflection. In addition, the actual path of the rays depends on both the refractive index and the refracting angle - the angle at the apex of the prism.)

Total reflection If light falls from an optically denser medium to an optically less dense one, then at a certain angle of incidence for each medium, the refracted beam disappears. Only refraction is observed. This phenomenon is called total internal reflection.
The angle of incidence, which corresponds to a refraction angle of 90°, is called the limiting angle of total internal reflection (a 0). From the law of refraction it follows that when light passes from any medium into vacuum (or air)
If we try to look from under the water at what is in the air, then at a certain angle at which we look, we can see the bottom reflected from the surface of the water. This is important to take into account in order not to lose orientation.
In jewelry, the cut of stones is selected so that full reflection is observed on each face. This explains the “game of stones”.
The phenomenon of mirage is also explained by total internal reflection.

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:

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:

With the help of experiments, the laws of reflection for light radiation were found back in the 3rd century. BC e. ancient Greek scientist Euclid. In modern conditions, verification of these laws is done using an optical washer (Fig. 29.2). It consists of a light source A, which can be moved around a disk divided into degrees. By directing light onto the reflective surface 3, angles are measured.

The laws of light reflection coincide with the laws of wave reflection from obstacles (§ 24.19).

1. The incident beam and the reflected beam lie in the same plane, perpendicular to the reflective surface, placed at the point of incidence of the beam.

2. The angle of reflection of the beam is equal to the angle of its incidence:

Using an optical washer, it can be shown that the incident and reflected rays are reversible, that is, if the incident ray is directed along the path of the reflected ray, then the reflected ray will follow the path of the incident ray.

In § 24.19 the laws of reflection for a spherical wave front were established. Let us now show that they are also valid for a plane wave front, that is, for the case of parallel rays falling on a flat surface.

Let a plane wave fall on a smooth surface (Fig. 29.3), the front of which at some point in time occupies the position. After some time, it will take the position . At this moment of time (we will take it to be zero), the reflected elementary wave will begin to propagate from point A. While the wave front moves from point C to point B in time, the wave from point

And it will spread across the hemisphere to a distance equal to the speed of wave propagation). The new position of the wave front after the reflection of the rays will be a tangent to the hemisphere drawn from point B, i.e. a straight line. Further, this wave front will move parallel to itself in the direction of the rays AA or

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.