Municipal budgetary educational institution - secondary

Secondary school No. 2 named after A.I. Herzen, Klintsy, Bryansk region

Lesson on the topic

Prepared and hosted:

Physics teacher

Prokhorenko Anna

Alexandrovna

Klintsy, 2013

Content:

Lesson on the topic “Wave phenomenon. Propagation of mechanical waves. Wavelength. Wave speed. »

The purpose of the lesson: introduce the concepts of wave, wave length and speed, wave propagation condition, types of waves, teach students to apply formulas for finding the length and speed of a wave; to study the causes of the propagation of transverse and longitudinal waves;

Methodical tasks:

Educational : familiarization of students with the origin of the term "wave, wavelength, wave speed"; show students the phenomenon of wave propagation, and also prove, with the help of experiments, the propagation of two types of waves: transverse and longitudinal.

Educational : to promote the development of speech, thinking, cognitive and general labor skills; to promote mastering the methods of scientific research: analysis and synthesis.

Educational :

Lesson type: learning new material.

Methods: verbal, visual, practical.

Equipment: computer, presentation.

Demos:

Transverse and longitudinal waves.

Propagation of transverse and longitudinal waves.

Lesson plan:

Organization of the beginning of the lesson.

motivational stage. Setting goals, objectives of the lesson.

Learning new material

Consolidation of new knowledge.

Summing up the lesson.

DURING THE CLASSES

1. Organizational stage

2. motivational stage. Setting goals, objectives of the lesson.

What did you see in these videos? (Waves)

What types of waves did you see?

Based on your answers, we will try to set goals for today's lesson with you, for this, let's remember what is the plan for studying the concept, in this case, the concept of a wave? (What is a wave, i.e. definition, types of waves, characteristics of waves)

In today's lesson, I will help you with the concepts of wave, wave length and speed, wave propagation condition, types of waves, teach students to apply formulas for finding the length and speed of a wave; to study the causes of the propagation of transverse and longitudinal waves;With to form a conscientious attitude to educational work, positive motivation for learning, communication skills; contribute to the education of humanity, discipline, aesthetic perception of the world.

1. Learning new material

Now you need, according to the plan, which is presented on the screen and on the sheets of paper on your desks, and after reading paragraphs 42 and 43, find the necessary information and write it out.

Plan:

Wave concept

Conditions for the occurrence of a wave

Wave source

What is needed for a wave to occur

Types of waves (definitions)

Wave - vibrations that propagate in space over time. Waves arise mainly due to elastic forces.

Wave features:

Mechanical waves can propagate only in some medium (substance): in a gas, in a liquid, in a solid.

A mechanical wave cannot arise in a vacuum.

The source of the waves are oscillating bodies that create a deformation of the medium in the surrounding space. (rice)

For the occurrence of a mechanical wave, it is necessary:

1. The presence of an elastic medium

2 . The presence of a source of vibrations - deformation of the medium

Wave types:

Transverse - in which oscillations occur perpendicular to the direction of wave movement. Occur only in solids.

Longitudinal- in which oscillations occur along the direction of wave propagation.Occur in any medium (liquids, gases, solids).

We consider a table summarizing previous knowledge. (Look at the presentation)

We conclude: mechanical wave:

the process of vibration propagation in an elastic medium;

in this case, energy is transferred from particle to particle;

there is no transfer of matter;

To create a mechanical wave, an elastic medium is needed: liquid, solid or gas.

And now we will consider and write down the main characteristics of the waves.

What quantities characterize the wave

Each wave propagates at a certain speed. Under speedvwaves understand the propagation velocity of the perturbation. The speed of a wave is determined by the properties of the medium in which this wave propagates. When a wave passes from one medium to another, its speed changes.

The wavelength λ is the distance over which the wave propagates in a time equal to the period of oscillations in it.

Main characteristics: λ=v* T, λ - wavelength m,vis the propagation velocity m/s, T is the wave period c.

4. Consolidation of new knowledge.

What is a wave?

Wave conditions?

What types of waves do you know?

Can a transverse wave propagate in water?

What is called wavelength?

What is the speed of wave propagation?

How to relate speed and wavelength?

We consider 2 types and determine where which wave is?

Solve problems:

Determine the wavelength at a frequency of 200 Hz if the wave propagation speed is 340 m/s. (68000 m=68 km)

On the surface of the water in the lake, the wave propagates at a speed of 6 m/s. A leaf of a tree floats on the surface of the water. Determine the frequency and period of oscillation of the leaf if the wavelength is 3 m. (0.5 m, 2 s -1 )

The wavelength is 2 m, and the speed of its propagation is 400 m/s. Determine how many complete oscillations this wave makes in 0.1 s (20)

We consider it interesting : Waves on the surface of a liquid are neither longitudinal nor transverse. If you throw a small ball on the surface of the water, you can see that it moves, swaying on the waves, along a circular path. Thus, a wave on the surface of a liquid is the result of the addition of the longitudinal and transverse motion of water particles.

5. Summing up the lesson.

So, let's sum up.

What words would you use to describe the state after the lesson?:

Knowledge is knowledge only when it is acquired by the efforts of one's thought, and not by memory;

Oh, how tired I am from this fuss ... ..

You understood the bliss of studies, luck, law and secret

Studying the topic "Mechanical waves" is not so easy!!!

6 . Information about homework.

Schedule responses to questions using §§42-44

It is good to know the formulas and definitions on the topic "Waves"

Optional: make a crossword on the topic "Mechanical waves"

Tasks:

The fisherman noticed that in 10 seconds the float made 20 oscillations on the waves, and the distance between adjacent wave humps was 1.2 m. What is the speed of wave propagation?(T=n/t; T=10/5=2c; λ=υ*ν; ν=1/T; λ=υ/T; υ=λ*T*υ=1*2=2(m/s ))

The length of the wave is 5 m, and its frequency is 3 Hz. Determine the speed of the wave. (1.6 m/s)

Introspection

The lesson was held in grade 11 on the topic “wave phenomenon. Propagation of mechanical waves. Wavelength. Wave speed.It is the thirteenth lesson in the physics section "Mechanical vibrations and waves." Type of lesson: learning new material.

The lesson took into account the triune didactic goal: educational, developmental, educational. I set the educational goal to familiarize students with the origin of the term "wave, wavelength, wave speed"; show students the phenomenon of wave propagation, and also prove with the help of experiments the existence of two types of waves: transverse and longitudinal. As a developing goal, I set the formation of students' clear ideas about the conditions for wave propagation; development of logical and theoretical thinking, imagination, memory in solving problems and consolidating ZUNs. I have set as an educational goal: to form a conscientious attitude to educational work, positive motivation for learning, communication skills; contribute to the education of humanity, discipline, aesthetic perception of the world.

During the lesson, we went through the following steps:

Organizational stage

Motivational and goal setting, lesson objectives. At this stage, based on the watched video clip, we determined the goals and objectives for the lesson and conducted motivation. Using: a verbal method in the form of a conversation, a visual method in the form of watching a video clip.

Learning new material

At this stage, I provided for a logical connection when explaining new material: consistency, accessibility, understandability. The main methods of the lesson were: verbal (conversation), visual (demonstrations, computer modeling). Form of work: individual.

Fixing new material

When fixing the students' ZUNs, I used interactive tasks from the multimedia manual in the "Mechanical Waves" section, solving problems at the blackboard with an explanation. The main methods of the lesson were: practical (problem solving), verbal (talk on questions)

Summarizing.

At this stage, I used the verbal method in the form of a conversation, the guys answered the questions posed.

Reflection done. We found out whether the goals set at the beginning of the lesson were achieved, which was difficult for them in this lesson. Two students were given marks for the tasks and several students were given marks for the answers.

Information about homework.

At this stage, students were asked to write down their homework in the form of an answer to a question according to the plan and a couple of tasks on a piece of paper. And optionally make a crossword puzzle.

I believe that the triune didactic goal of the lesson has been achieved.

24-25. Wave phenomena. Propagation of mechanical waves. Wavelength. Wave propagation speed. Problem solving.

Physics teacher

Razdolnenskaya school I - III steps

Department of Education of the Administration of the Starobeshevsky District

We turn to the study of issues related to waves. Let's talk about what a wave is, how it appears and what it is characterized by. It turns out that in addition to just an oscillatory process in a narrow region of space, it is also possible to propagate these oscillations in a medium, and it is precisely such propagation that is wave motion.

Let's move on to a discussion of this distribution. To discuss the possibility of the existence of oscillations in a medium, we must define what a dense medium is. A dense medium is a medium that consists of a large number of particles whose interaction is very close to elastic. Imagine the following thought experiment.

Rice. 1. Thought experiment

Let us place a sphere in an elastic medium. The ball will shrink, decrease in size, and then expand like a heartbeat. What will be observed in this case? In this case, the particles that are adjacent to this ball will repeat its movement, i.e. move away, approach - thereby they will oscillate. Since these particles interact with other particles more distant from the ball, they will also oscillate, but with some delay. Particles that are close to this ball, oscillate. They will be transmitted to other particles, more distant. Thus, the oscillation will propagate in all directions. Note that in this case, the oscillation state will propagate. This propagation of the state of oscillations is what we call a wave. It can be said that

The process of propagation of vibrations in an elastic medium over time is called a mechanical wave.

Please note: when we talk about the process of occurrence of such oscillations, we must say that they are possible only if there is an interaction between particles. In other words, a wave can exist only when there is an external perturbing force and forces that oppose the action of the perturbing force. In this case, these are elastic forces.

Mechanical waves can propagate in an elastic medium .

An elastic medium is a medium that consists of a large number of particles interacting with each other by elastic forces.

The propagation process in this case will be related to the density and strength of interaction between the particles of this medium.

Let's note one more thing.

The wave does not carry matter . After all, particles oscillate near the equilibrium position. But at the same time, the wave carries energy. This fact can be illustrated by tsunami waves. Matter is not carried by the wave, but the wave carries such energy that brings great disasters.

Let's talk about the types of waves. There are two types - longitudinal and transverse waves. What longitudinal waves? These waves can exist in all media. And the example with a pulsating ball inside a dense medium is just an example of the formation of a longitudinal wave. Such a wave is a propagation in space over time. This alternation of compaction and rarefaction is a longitudinal wave. I repeat once again that such a wave can exist in all media - liquid, solid, gaseous.

A longitudinal wave is a wave, during the propagation of which the particles of the medium oscillate along the direction of wave propagation.

R is. 2. Longitudinal wave

As for the transverse wave, transverse wave can exist only in solids and on the surface of a liquid.

A wave is called a transverse wave, during the propagation of which the particles of the medium oscillate perpendicular to the direction of wave propagation.

Rice. 3. Shear wave

The propagation speed of longitudinal and transverse waves is different, but this is the topic of the next lessons.

Figure "Longitudinal and transverse waves"

Wavelength. Wave propagation speed

The lesson is devoted to the topic "Characteristics of wave motion." To begin with, let's remember that mechanical wave is an oscillation that propagates over time in an elastic medium. Since this is an oscillation, the wave will have all the characteristics that correspond to the oscillation: amplitude, oscillation period and frequency. In addition, the wave has its own special characteristics. One of these characteristics is wavelength. Wavelength is denoted by the Greek letter l (lambda, or they say "lambda") and is measured in meters.

A - amplitude [m]

T - period [s]

ν – frequency [Hz]

l - wavelength [m]

What is a wavelength?

The wavelength is the smallest distance between particles that oscillate with the same phase.

Rice. 1. Wavelength, wave amplitude

It is more difficult to talk about the wavelength in a longitudinal wave, because it is much more difficult to observe particles that make the same vibrations there. But there is also a characteristic wavelength, which determines the distance between two particles making the same oscillation, oscillation with the same phase.

The next characteristic is the speed of wave propagation (or simply the speed of the wave). Wave speed It is denoted, like any other speed, by the letter V and is measured in m / s. How to clearly explain what is the speed of the wave? The easiest way to do this is with a transverse wave as an example. Imagine a seagull flying over the crest of a wave. Its flight speed over the crest will be the speed of the wave itself.

Rice. 2. To the definition of wave speed

Wave speed depends on what is the density of the medium, what are the forces of interaction between the particles of this medium. Let's write down the relationship between the wave speed, wavelength and wave period: . Formula "Wavelength"

Speed ​​can be defined as the ratio of the wavelength, the distance traveled by the wave in 1 period, to the period of oscillation of the particles of the medium in which the wave propagates. In addition, remember that . Then we have one more relation for the wave speed: V = lν.

It is important to note that

when a wave passes from one medium to another, its characteristics change: the speed of the wave, the wavelength. But the oscillation frequency remains the same.

Waves in nature and technology

Interactive task

Before we get started, let's answer the following questions:

1. What is the main property of all waves, regardless of their nature?
2. Why can't transverse waves exist in gases and liquids?
3. What body can create a sound wave in the environment?

Solve problems on the application of the above material:

When solving problems, the speed of sound in air is assumed to be given and equal to 330 m/s.
1. In the oceans, the wavelength reaches 300 m, and the period is 13.5 s. Determine the propagation speed of such a wave.
2. Determine the length of the sound wave at a frequency of 200 Hz.
3. The observer heard the sound of an artillery shot 6 seconds after seeing the flash. How far away was the gun?
4. The length of the sound waves emitted by the violin. can vary from 23 mm to 1.3 m. What is the frequency range of the violin?
5. The distance to the barrier that reflects the sound is 66 m. How long will it take for a person to hear an echo?

You can offer a number of tasks and solve them using a tablet, for example, R Nos. 439-444.

Homework:Paragraphs 42-44, exercise 6, page 129.

What is called a wave? Why do waves occur?
Separate particles of any body - solid, liquid or gaseous - interact with each other. Therefore, if a deformation occurs in any section of the elastic medium, then after the termination of external influences, it will not remain in place, but will begin to spread in the medium in all directions.
A change in the state of the medium that propagates in space over time is called a wave.
In air, in solids and inside liquids, mechanical waves arise due to elastic forces (elastic waves). These forces carry out the connection between the individual parts of the body. In the formation of waves on the surface of water, gravity and surface tension (surface waves) play a role.
Wave impulse and harmonic waves
Waves can have different shapes. A wave impulse (or a single wave) is a relatively short perturbation (burst) of arbitrary shape. Such an impulse occurs, for example, in a rubber cord tied to a wall, if you wave your hand once, holding

cabbage soup opposite end of the growing | drawn cord (Fig. 4.2). | If the perturbation of the environment causes- | If a periodic external force changes with time according to a harmonic law, then the waves it causes are called harmonic. In this case, at each point of the medium, harmonic oscillations occur with the frequency of the external action. We will mainly consider harmonic waves or waves close to harmonic. This is the simplest form of wave motion. The study of harmonic waves is of paramount importance in constructing the theory of any wave motion.
The main feature of wave motion

A visual representation of the main features of wave motion can be obtained by considering waves on the surface of water. Waves have the form of rounded shafts running forward (Fig. 4.3). The distances between the shafts, or ridges, are approximately the same. However, if a light object, such as a matchbox, is thrown into the water, then it will not be carried forward by the wave, but will begin to oscillate up and down, remaining almost exactly in one place.
When a wave propagates, the form moves (moves a certain state of the oscillating medium), but not the transfer of matter in which the wave propagates. Water disturbances that have arisen in one place, for example, from a thrown stone, are transmitted to neighboring areas and gradually spread in all directions. The flow of water does not arise: only the shape of its surface moves.
Wave speed
The most important characteristic of a wave is the speed of its propagation. Waves of any nature do not propagate through space instantly. Their speed is finite. One can imagine, for example, that a seagull flies over the sea in such a way that it always finds itself above the same crest of a wave. The speed of the wave in this case will be equal to the speed of the seagull. Waves on the surface of the water are convenient for observation because the speed of their propagation is low.
Transverse and longitudinal waves
It is not difficult for TE.KZh6 to observe waves propagating along a rubber cord. If one end of the cord is fixed and, slightly pulling the cord with your hand, bring its other end into oscillatory motion, then a wave will run along the cord (Fig. 4.4). The speed of the wave will be the greater, the stronger the cord is pulled. The wave will reach the point of fixation, be reflected and run back. Here, when the wave propagates, the shape of the cord changes. Each section of the cord oscillates about its invariable position of equilibrium. Pay attention to the fact that when a wave propagates along the cord, its individual sections oscillate in a direction perpendicular to the direction of propagation.
6 - 5654
Rice. 4.4
Oscillation direction
wave propagation

Direction
Rice. 4.5 waves (Fig. 4.5). Such waves are called transverse.
But not every wave is transverse. Oscillations can also occur along the direction of wave propagation (Fig. 4.6). Then the wave is called longitudinal. It is convenient to observe the longitudinal wave with the help of a long soft spring of large diameter. By hitting one of the ends of the spring with your palm (Fig. 4.7, a), you can see how the compression (elastic impulse) runs along the spring. With the help of a series of successive impacts, it is possible to excite a wave in the spring, which is a successive compression and extension of the spring, running one after another (Fig. 4.7.6). Oscillations of any coil of the spring occur in the direction of wave propagation.
Of the mechanical waves, sound waves are the most important. However, the study of sound waves is a more difficult task than the study of waves along a cord or spring. We will deal with them in detail later.
wave energy
When a wave propagates, motion is transferred from one part of the body to another. The transfer of motion by a wave is associated with the transfer of energy without the transfer of matter. The energy comes from a source that excites vibrations at the beginning of the cord, string, etc., and propagates along with the wave. This energy, for example, in a cord is composed of the kinetic energy
Direction of wave propagation oscillations
Rice. 4.7
dshshshshr
b) the energy of movement of sections of the cord and the potential energy of its elastic deformation.
The wave energy from a stone thrown into the water increases the kinetic energy of the float on the surface of the water, and can also increase the potential energy of a chip floating near the shore.
When the wave propagates, there is a gradual decrease in the amplitude of oscillations due to the transformation of part of the mechanical energy into internal energy. If these losses can be neglected, then the same amount of mechanical energy will pass through the cross section of, for example, a cord per unit time.
Electromagnetic waves
Mechanical waves propagate in matter: gas, liquid or solid. There is, however, another kind of wave that does not need any substance to propagate. These are electromagnetic waves, which, in particular, include radio waves and light. An electromagnetic field can exist in a vacuum (in a void), that is, in a space that does not contain atoms. Despite all the unusual nature of these waves, their sharp difference from mechanical waves, electromagnetic waves during their propagation behave like mechanical waves. In particular, electromagnetic waves also propagate at a finite speed and carry energy with them. These are the most important properties of all types of waves.

Basic Laws of Dynamics. Newton's laws - first, second, third. Galileo's principle of relativity. The law of universal gravitation. Gravity. Forces of elasticity. The weight. Friction forces - rest, sliding, rolling + friction in liquids and gases.

Kinematics. Basic concepts. Uniform rectilinear motion. Uniform movement. Uniform circular motion. Reference system. Trajectory, displacement, path, equation of motion, speed, acceleration, relationship between linear and angular velocity.

simple mechanisms. Lever (lever of the first kind and lever of the second kind). Block (fixed block and movable block). Inclined plane. Hydraulic Press. The golden rule of mechanics

Conservation laws in mechanics. Mechanical work, power, energy, law of conservation of momentum, law of conservation of energy, equilibrium of solids

Circular movement. Equation of motion in a circle. Angular velocity. Normal = centripetal acceleration. Period, frequency of circulation (rotation). Relationship between linear and angular velocity

Mechanical vibrations. Free and forced vibrations. Harmonic vibrations. Elastic oscillations. Mathematical pendulum. Energy transformations during harmonic vibrations

mechanical waves. Velocity and wavelength. Traveling wave equation. Wave phenomena (diffraction, interference...)

Hydromechanics and Aeromechanics. Pressure, hydrostatic pressure. Pascal's law. Basic equation of hydrostatics. Communicating vessels. Law of Archimedes. Sailing conditions tel. Fluid flow. Bernoulli's law. Torricelli formula

Molecular physics. Basic provisions of the ICT. Basic concepts and formulas. Properties of an ideal gas. Basic equation of the MKT. Temperature. The equation of state for an ideal gas. Mendeleev-Klaiperon equation. Gas laws - isotherm, isobar, isochore

Wave optics. Corpuscular-wave theory of light. Wave properties of light. dispersion of light. Light interference. Huygens-Fresnel principle. Diffraction of light. Light polarization

Thermodynamics. Internal energy. Job. Quantity of heat. Thermal phenomena. First law of thermodynamics. Application of the first law of thermodynamics to various processes. Heat balance equation. The second law of thermodynamics. Heat engines

Electrostatics. Basic concepts. Electric charge. The law of conservation of electric charge. Coulomb's law. The principle of superposition. The theory of close action. Electric field potential. Capacitor.

Constant electric current. Ohm's law for a circuit section. Operation and DC power. Joule-Lenz law. Ohm's law for a complete circuit. Faraday's law of electrolysis. Electrical circuits - serial and parallel connection. Kirchhoff's rules.

Electromagnetic vibrations. Free and forced electromagnetic oscillations. Oscillatory circuit. Alternating electric current. Capacitor in AC circuit. An inductor ("solenoid") in an alternating current circuit.

You are here now: Electromagnetic waves. The concept of an electromagnetic wave. Properties of electromagnetic waves. wave phenomena

A magnetic field. Magnetic induction vector. The gimlet rule. Ampere's law and Ampere's force. Lorentz force. Left hand rule. Electromagnetic induction, magnetic flux, Lenz's rule, law of electromagnetic induction, self-induction, magnetic field energy

The quantum physics. Planck's hypothesis. The phenomenon of the photoelectric effect. Einstein's equation. Photons. Bohr's quantum postulates.

Elements of the theory of relativity. Postulates of the theory of relativity. Relativity of simultaneity, distances, time intervals. Relativistic law of addition of velocities. The dependence of mass on speed. The basic law of relativistic dynamics...

Errors of direct and indirect measurements. Absolute, relative error. Systematic and random errors. Standard deviation (error). Table for determining the errors of indirect measurements of various functions.

These phenomena are inherent in waves of any nature. Moreover, the phenomena of interference, diffraction, and polarization are characteristic only of wave processes and can only be explained on the basis of wave theory.

Reflection and refraction. The propagation of waves is geometrically described using rays. In a homogeneous environment ( n= const) the rays are rectilinear. However, at the interface between the media, their directions change. In this case, two waves are formed: a reflected one, propagating in the first medium with the same speed, and a refracted one, propagating in the second medium with a different speed, depending on the properties of this medium. The phenomenon of reflection is known for both sound (echo) and light waves. Due to the reflection of light, an imaginary image is formed in the mirror. The refraction of light underlies many interesting atmospheric phenomena. It is widely used in various optical devices: lenses, prisms, optical fibers. These devices are elements of devices for various purposes: cameras, microscopes and telescopes, periscopes, projectors, optical communication systems, etc.

Interference waves - the phenomenon of energy redistribution when two (or several) coherent (matched) waves are superimposed, accompanied by the appearance of an interference pattern of alternating maxima and minima of the intensity (amplitude) of the resulting wave. Waves are called coherent, for which the phase difference at the point of addition remains unchanged in time, but can change from point to point and in space. If the waves meet "in phase", i.e. simultaneously reach the maximum deviation in one direction, then they reinforce each other, and if they meet "in antiphase", i.e. simultaneously achieve opposite deviations, then weaken each other. Coordination of oscillations of two waves (coherence) of two waves in the case of light is possible only if they have a common origin, which is due to the peculiarities of the radiation processes. The exception is lasers, whose radiation is characterized by high coherence. Therefore, to observe interference, light coming from one source is divided into two groups of waves, either passing through two holes (slits) in an opaque screen, or due to reflection and refraction at the interface of media in thin films. Interference pattern from a monochromatic source ( λ=const) on the screen for rays passing through two narrow closely spaced slits, has the form of alternating bright and dark stripes (Jung's experiment, 1801). Bright stripes - intensity maxima are observed at those points of the screen where the waves from two slots meet "in phase", i.e. their phase difference

, m =0,1,2,…,(3.10)

This corresponds to the difference in the path of the rays, a multiple of an integer number of wavelengths λ

, m =0,1,2,…,(3.11)

Dark bars (mutual repayments), i.e. intensity minima occur at those points of the screen at which the waves meet "out of phase", i.e., their phase difference is

, m =0,1,2,…,(3.12)

This corresponds to the difference in the path of the rays, a multiple of an odd number of half-waves

, m =0,1,2,….(3.13)

Interference is observed for different waves. Interference of white light, including all wavelengths of visible light in the wavelength range microns can appear as iridescent coloration of thin films of gasoline on the surface of water, soap bubbles, oxide films on the surface of metals. The conditions of the interference maximum at different points of the film are satisfied for different waves with different wavelengths, which leads to amplification of waves of different colors. The interference conditions are determined by the wavelength, which for visible light is a fraction of a micron (1 μm = 10 -6 m), so this phenomenon underlies various precision (“high-precision”) methods of research, control and measurement. The use of interference is based on the use of interferometers, interference spectroscopes, as well as the holography method. Light interference is used to measure the wavelength of radiation, study the fine structure of spectral lines, determine densities, refractive indices of substances, and the thickness of thin coatings.

Diffraction- a set of phenomena that occur during the propagation of a wave in a medium with a pronounced inhomogeneity of properties. This is observed when waves pass through a hole in the screen, near the border of opaque objects, etc. Diffraction causes the wave to wrap around an obstacle whose dimensions are commensurate with the wavelength. If the size of the obstacle is much larger than the wavelength, then the diffraction is weak. On macroscopic obstacles, diffraction of sound, seismic waves, radio waves is observed, for which 1 cm km. To observe the diffraction of light, the obstacles must be substantially smaller. The diffraction of sound waves explains the ability to hear the voice of a person who is around the corner of the house. The diffraction of radio waves around the Earth's surface explains the reception of radio signals in the range of long and medium radio waves far beyond the line of sight of the emitting antenna.

The diffraction of waves is accompanied by their interference, which leads to the formation of a diffraction pattern, alternating intensity maxima and minima. When light passes through a diffraction grating, which is a set of alternating parallel transparent and opaque bands (up to 1000 per 1 mm), a diffraction pattern appears on the screen, the position of the maxima of which depends on the radiation wavelength. This makes it possible to use a diffraction grating to analyze the spectral composition of radiation. The structure of a crystalline substance is similar to a three-dimensional diffraction grating. Observation of the diffraction pattern during the passage of X-rays, a beam of electrons or neurons through crystals in which particles of a substance (atoms, ions, molecules) are arranged in an orderly manner, makes it possible to study the features of their structure. The characteristic value for interatomic distances is d ~ 10 -10 m, which corresponds to the wavelengths of the radiation used and makes them indispensable for crystallographic analysis.

The diffraction of light determines the limit of the resolution of optical instruments (telescopes, microscopes, etc.). Resolution - the minimum distance between two objects at which they are seen separately, do not merge - are allowed. Due to diffraction, the image of a point source (for example, a star in a telescope) looks like a circle, so objects that are close together are not resolved. The resolution depends on a number of parameters, including the wavelength: the shorter the wavelength, the better the resolution. Therefore, the size of an object observed in an optical microscope is limited by the wavelength of light (approximately 0.5 µm).

The phenomenon of interference and diffraction of light underlies the principle of recording and reproducing images in holography. The method proposed in 1948 by D. Gabor (1900 - 1979) fixes the interference pattern obtained by illuminating an object and a photographic plate with coherent beams. The resulting hologram is an alternating light and dark spots that do not resemble the object, however, diffraction from the hologram of light waves identical to those used when recording it, allows you to restore the wave scattered by the real object and obtain its three-dimensional image.

Polarization- a phenomenon characteristic only of transverse waves. The transverseness of light waves (as well as any other electromagnetic waves) is expressed in the fact that the vectors of electric () and magnetic induction () fields oscillating in them are perpendicular to the direction of wave propagation. In addition, these vectors are mutually perpendicular; therefore, to fully describe the state of polarization of light, it is required to know the behavior of only one of them. The action of light on the recording devices is determined by the electric field strength vector, which is called the light vector.

Light waves emitted by a natural source of radiation i.e. set of independent atoms, are not polarized, because the direction of oscillation of the light vector () in a natural beam will change continuously and randomly, remaining perpendicular to the wave velocity vector.

Light in which the direction of the light vector remains unchanged is called linearly polarized. Polarization is the ordering of vector oscillations. An example is a harmonic wave. To polarize light, devices called polarizers are used, the action of which is based on the features of the processes of reflection and refraction of light, as well as on the anisotropy of the optical properties of a substance in the crystalline state. The light vector in the beam passing through the polarizer oscillates in a plane called the plane of the polarizer. When polarized light passes through the second polarizer, it turns out that the intensity of the transmitted beam changes with the rotation of the polarizer. Light passes through the device without absorption if its polarization coincides with the plane of the second polarizer and is completely blocked by it when the crystal is rotated by 90 degrees, when the plane of oscillations of the polarized light is perpendicular to the plane of the second polarizer.

The polarization of light has found wide application in various branches of scientific research and technology. it is used in microscopic research, in sound recording, optical location, high-speed film and photography, in the food industry (saccharimetry), etc.

Dispersion- dependence of the wave propagation velocity on their frequency (wavelength). When electromagnetic waves propagate in a medium, there arises -

The dispersion is determined by the physical properties of the medium in which the waves propagate. For example, in a vacuum, electromagnetic waves propagate without dispersion, while in a real medium, even in such a rarefied one as the Earth's ionosphere, dispersion arises. Sonic and ultrasonic waves also detect dispersion. When they propagate in a medium, harmonic waves of different frequencies, into which a signal can be decomposed, propagate at different speeds, which leads to distortion of the signal shape. Dispersion of light - the dependence of the refractive index of a substance on the frequency (wavelength) of light. When the speed of light changes, depending on the frequency (wavelength), the refractive index changes. As a result of dispersion, white light, consisting of many waves of different frequencies, decomposes when passing through a transparent trihedral prism and forms a continuous (continuous) spectrum. The study of this spectrum led I. Newton (1672) to the discovery of the dispersion of light. For substances that are transparent in a given region of the spectrum, the refractive index increases with increasing frequency (decreasing wavelength), which corresponds to the distribution of colors in the spectrum. The highest refractive index is for violet light (=0.38 µm), the lowest for red (=0.76 µm). A similar phenomenon is observed in nature during the propagation of sunlight in the atmosphere and its refraction in particles of water (in summer) and ice (in winter). This creates a rainbow or solar halo.

Doppler effect. The Doppler effect is a change in the frequency or wavelength perceived by the observer (receiver) due to the movement of the wave source and the observer relative to each other. Wave speed u is determined by the properties of the medium and does not change when the source or observer moves. If the observer or wave source moves at a speed relative to the medium, then the frequency v received waves becomes different. In this case, as established by K. Doppler (1803 - 1853), when the observer approaches the source, the frequency of the waves increases, and when removed, it decreases. This corresponds to a decrease in the wavelength λ as the source and observer approach each other and increase λ when they are mutually removed. For sound waves, the Doppler effect manifests itself in the increase in the pitch of the sound when the sound source and the observer approach each other (for 1 sec the observer perceives a larger number of waves), and correspondingly in the lowering of the tone of the sound when they are removed. The Doppler effect also causes the "redshift", as described above. - lowering the frequencies of electromagnetic radiation from a moving source. This name is due to the fact that in the visible part of the spectrum, as a result of the Doppler effect, the lines are shifted to the red end; "Redshift" is also observed in radiation of any other frequencies, for example, in the radio range. The opposite effect associated with increasing frequencies is called blue (or violet) shift. In astrophysics, two "redshifts" are considered - cosmological and gravitational. Cosmological (metagalactic) refers to the "redshift" observed for all distant sources (galaxies, quasars) - a decrease in radiation frequencies, indicating the removal of these sources from each other and, in particular, from our Galaxy, i.e., non-stationarity (expansion ) Metagalaxies. "Redshift" for galaxies was discovered by the American astronomer W. Slifer in 1912-14; in 1929, E. Hubble discovered that for distant galaxies it is greater than for nearby ones, and increases approximately in proportion to the distance. This made it possible to reveal the law of mutual removal (retreat) of galaxies. Hubble's law in this case is written in the form

u = HR; (3.14)

(u is the receding speed of the galaxy, r- distance to it, H - Hubble constant). Determining by the magnitude of the "redshift" the speed of removal of the galaxy, you can calculate the distance to it. To determine the distances to extragalactic objects using this formula, you need to know the numerical value of the Hubble constant N. The knowledge of this constant is also very important for cosmology: the definition of the "age" of the Universe is connected with it. In the early 1970s, the Hubble constant was taken to be H =(3 – 5)*10 -18 s -1 , reciprocal T = 1/H = 18 billion years. The gravitational "redshift" is a consequence of the slowing down of the pace of time and is due to the gravitational field (the effect of the general theory of relativity). This phenomenon is also called the Einstein effect or the generalized Doppler effect. It has been observed since 1919, first in the radiation of the Sun, and then in some other stars. In some cases (for example, during gravitational collapse) "redshift" of both types should be observed.