Vladimir regional
industrial - commercial
lyceum

essay

Electromagnetic waves

Completed:
student 11 "B" class
Lvov Mikhail
Checked:

Vladimir 2001

Plan

1. Introduction ……………………………………………………… 3

2. The concept of a wave and its characteristics……………………………… 4

3. Electromagnetic waves………………………………………… 5

4. Experimental proof of existence
electromagnetic waves………………………………………… 6

5. Density of electromagnetic radiation flux ……………. 7

6. The invention of radio……………………………………………….… 9

7. Properties of electromagnetic waves …………………………………10

8. Modulation and detection…………………………………… 10

9. Types of radio waves and their propagation…………………………… 13

Introduction

Wave processes are extremely widespread in nature. There are two types of waves in nature: mechanical and electromagnetic. Mechanical waves propagate in matter: gas, liquid or solid. Electromagnetic waves do not need any substance for their propagation, which, in particular, include radio waves and light. An electromagnetic field can exist in a vacuum, that is, in a space that does not contain atoms. Despite the significant difference between electromagnetic waves and mechanical waves, electromagnetic waves during their propagation behave like mechanical waves. But like oscillations, all types of waves are described quantitatively by the same or almost the same laws. In my work, I will try to consider the causes of electromagnetic waves, their properties and applications in our lives.

The concept of a wave and its characteristics

wave called vibrations that propagate in space over time.

The most important characteristic of a wave is its speed. Waves of any nature do not propagate through space instantly. Their speed is finite.

When a mechanical wave propagates, motion is transmitted from one part of the body to another. The transfer of motion is associated with the transfer of energy. The main property of all waves, regardless of their nature, is their 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. Energy flows continuously through any cross section. This energy is composed of the kinetic energy of the movement of the sections of the cord and the potential energy of its elastic deformation. A gradual decrease in the amplitude of oscillations during the propagation of a wave is associated with the transformation of a part mechanical energy into the inner.

If the end of a stretched rubber cord is made to oscillate harmonically with a certain frequency v, then these vibrations will begin to propagate along the cord. Oscillations of any section of the cord occur with the same frequency and amplitude as the oscillations of the end of the cord. But only these oscillations are shifted in phase relative to each other. Such waves are called monochromatic.

If the phase shift between the oscillations of two points of the cord is equal to 2n, then these points oscillate in exactly the same way: after all, cos (2lvt + 2n) \u003d =cos2nvt. Such fluctuations are called in-phase(occur in the same phases).

The distance between points closest to each other, oscillating in the same phases, is called the wavelength.

Relationship between wavelength λ, frequency v and wave propagation speed c. For one period of oscillations, the wave propagates over a distance λ. Therefore, its speed is determined by the formula

Since the period T and frequency v are related by T = 1 / v

The speed of a wave is equal to the product of the wavelength and the oscillation frequency.

Electromagnetic waves

We now turn to the consideration of electromagnetic waves directly.

The fundamental laws of nature can give much more than is contained in the facts on the basis of which they are derived. One of these are the laws of electromagnetism discovered by Maxwell.

Among the countless, very interesting and important consequences, arising from the Maxwellian laws of the electromagnetic field, one deserves special attention. This is the conclusion that the electromagnetic interaction propagates at a finite speed.

According to the theory of short-range action, moving a charge changes the electric field near it. This alternating electric field generates an alternating magnetic field in neighboring regions of space. An alternating magnetic field, in turn, generates an alternating electric field, etc.

The movement of the charge thus causes a "burst" of the electromagnetic field, which, while spreading, covers all large areas of the surrounding space.

Maxwell proved mathematically that the propagation speed of this process is equal to the speed of light in vacuum.

Imagine that the electric charge is not just shifted from one point to another, but is brought into rapid oscillations along some straight line. Then the electric field in the immediate vicinity of the charge will begin to change periodically. The period of these changes will obviously be equal to the period of charge oscillations. An alternating electric field will generate a periodically changing magnetic field, and the latter, in turn, will cause the appearance of an alternating electric field already at a greater distance from the charge, etc.

At every point in space, electrical and magnetic fields change periodically over time. The farther the point is from the charge, the later its field oscillations will reach. Consequently, at different distances from the charge, oscillations occur with different phases.

The directions of the oscillating vectors of the electric field strength and magnetic field induction are perpendicular to the direction of wave propagation.

The electromagnetic wave is transverse.

Electromagnetic waves are emitted by oscillating charges. It is essential that the speed of movement of such charges varies with time, i.e., that they move with acceleration. The presence of acceleration is the main condition for the radiation of electromagnetic waves. The electromagnetic field is radiated in a noticeable way, not only when the charge fluctuates, but also with any rapid change in its speed. The intensity of the emitted wave is the greater, the greater the acceleration with which the charge moves.

Maxwell was deeply convinced of the reality of electromagnetic waves. But he did not live to see their experimental discovery. Only 10 years after his death, electromagnetic waves were experimentally obtained by Hertz.

Experimental proof of existence

electromagnetic waves

Electromagnetic waves are not visible, unlike mechanical waves, but then how were they detected? To answer this question, consider the experiments of Hertz.

An electromagnetic wave is formed due to the interconnection of alternating electric and magnetic fields. Changing one field leads to the appearance of another. As you know, the faster the magnetic induction changes with time, the greater the strength of the emerging electric field. And in turn, the faster the electric field changes, the greater the magnetic induction.

For the formation of intense electromagnetic waves, it is necessary to create electromagnetic oscillations of a sufficiently high frequency.

High frequency oscillations can be obtained using an oscillatory circuit. The oscillation frequency is 1/ √ LC. From here it can be seen that it will be the greater, the smaller the inductance and capacitance of the circuit.

To obtain electromagnetic waves, G. Hertz used a simple device, now called the Hertz vibrator.

This device is an open oscillatory circuit.

It is possible to switch to an open circuit from a closed circuit if the capacitor plates are gradually moved apart, reducing their area and at the same time reducing the number of turns in the coil. In the end, it will just be a straight wire. This is the open oscillatory circuit. The capacitance and inductance of the Hertz vibrator are small. Therefore, the oscillation frequency is very high.

In an open circuit, the charges are not concentrated at the ends, but are distributed throughout the conductor. The current at a given time in all sections of the conductor is directed in the same direction, but the current strength is not the same in different sections of the conductor. At the ends, it is equal to zero, and in the middle it reaches a maximum (in conventional AC circuits, the current strength in all sections is the same at a given time.) The electromagnetic field also covers the entire space near the circuit.

Hertz received electromagnetic waves by exciting a series of fast-alternating current pulses in a vibrator using a high voltage source. Oscillations of electric charges in the vibrator create an electromagnetic wave. Only oscillations in the vibrator are performed not by one charged particle, but by a huge number of electrons moving in concert. In an electromagnetic wave, the vectors E and B are perpendicular to each other. Vector E lies in a plane passing through the vibrator, and vector B is perpendicular to this plane. The radiation of waves occurs with maximum intensity in the direction perpendicular to the axis of the vibrator. There is no radiation along the axis.

Electromagnetic waves were recorded by Hertz using a receiving vibrator (resonator), which is the same device as the radiating vibrator. Under the action of an alternating electric field of an electromagnetic wave, current oscillations are excited in the receiving vibrator. If the natural frequency of the receiving vibrator coincides with the frequency of the electromagnetic wave, resonance is observed. Oscillations in the resonator occur with a large amplitude when it is located parallel to the radiating vibrator. Hertz detected these vibrations by observing sparks in a very small gap between the conductors of the receiving vibrator. Hertz not only received electromagnetic waves, but also discovered that they behave like other kinds of waves.

By calculating the natural frequency of the electromagnetic oscillations of the vibrator. Hertz was able to determine the speed of an electromagnetic wave by the formula c \u003d λ v . It turned out to be approximately equal to the speed of light: c = 300,000 km/s. Hertz's experiments brilliantly confirmed Maxwell's predictions.

Flux density of electromagnetic radiation

Now let's move on to the consideration of the properties and characteristics of electromagnetic waves. One of the characteristics of electromagnetic waves is the density of electromagnetic radiation.

Consider a surface with an area S through which electromagnetic waves carry energy.

The electromagnetic radiation flux density I is the ratio of electromagnetic energy Wpassing in time t through a surface perpendicular to the rays with an area S, to the product of the area S and time t.

The radiation flux density, in SI, is expressed in watts per square meter (W / m 2). Sometimes this quantity is called the intensity of the wave.

After a series of transformations, we get that I = w c.

i.e., the density of the radiation flux is equal to the product of the density of electromagnetic energy and the speed of its propagation.

We have met more than once with the idealization of real sources of acceptance in physics: a material point, an ideal gas, etc. Here we will meet with one more.

A radiation source is considered to be a point source if its dimensions are much smaller than the distance at which its effect is estimated. In addition, it is assumed that such a source sends electromagnetic waves in all directions with the same intensity.

Let us consider the dependence of the radiation flux density on the distance to the source.

The energy that electromagnetic waves carry with them is distributed over a larger and larger surface over time. Therefore, the energy transferred through a unit area per unit time, i.e., the radiation flux density, decreases with distance from the source. It is possible to find out the dependence of the radiation flux density on the distance to the source by placing a point source in the center of a sphere with a radius R. the surface area of ​​the sphere S= 4 n R^2. If we assume that the source in all directions during the time t radiates energy W

The radiation flux density from a point source decreases in inverse proportion to the square of the distance to the source.

Let us now consider the frequency dependence of the radiation flux density. As you know, the radiation of electromagnetic waves occurs during the accelerated movement of charged particles. The strength of the electric field and the magnetic induction of an electromagnetic wave are proportional to the acceleration a emitting particles. Harmonic acceleration is proportional to the square of the frequency. Therefore, the electric field strength and magnetic induction are proportional to the square of the frequency

The energy density of the electric field is proportional to the square of the field strength. The energy of the magnetic field is proportional to the square of the magnetic induction. The total energy density of the electromagnetic field is equal to the sum of the energy densities of the electric and magnetic fields. Therefore, the radiation flux density is proportional to: (E^2+B^2). From here we get that I is proportional to w^4.

The radiation flux density is proportional to the fourth power of the frequency.

invention of radio

Hertz's experiments interested physicists all over the world. Scientists began to look for ways to improve the emitter and receiver of electromagnetic waves. In Russia, Alexander Stepanovich Popov, a teacher of officer courses in Kronstadt, was one of the first to study electromagnetic waves.

A. S. Popov used a coherer as a part that directly “feels” electromagnetic waves. This device is a glass tube with two electrodes. Small metal filings are placed in the tube. The operation of the device is based on the effect of electrical discharges on metal powders. Under normal conditions, the coherer has a high resistance, since the sawdust has poor contact with each other. The incoming electromagnetic wave creates a high-frequency alternating current in the coherer. The smallest sparks jump between the sawdust, which sinter the sawdust. As a result, the resistance of the coherer drops sharply (in the experiments of A.S. Popov from 100,000 to 1000-500 ohms, i.e., by a factor of 100-200). You can return the device to high resistance again by shaking it. To ensure the automatic reception necessary for wireless communication, A. S. Popov used a ringing device to shake the coherer after receiving the signal. The electric bell circuit was closed by means of a sensitive relay at the moment of arrival of an electromagnetic wave. With the end of the reception of the wave, the work of the bell immediately stopped, since the hammer of the bell struck not only the bell cup, but also the coherer. With the last shake of the coherer, the apparatus was ready to receive a new wave.

To increase the sensitivity of the device, A. S. Popov grounded one of the coherer leads and connected the other to a highly raised piece of wire, creating the first receiving antenna for wireless communication. Grounding turns the conductive surface of the earth into part of an open oscillatory circuit, which increases the reception range.

Although modern radio receivers bear very little resemblance to A. S. Popov's receiver, the basic principles of their operation are the same as in his device. A modern receiver also has an antenna in which the incoming wave causes very weak electromagnetic oscillations. As in the receiver of A. S. Popov, the energy of these oscillations is not used directly for reception. Weak signals only control the energy sources that feed the subsequent circuits. Now such control is carried out using semiconductor devices.

On May 7, 1895, at a meeting of the Russian Physical and Chemical Society in St. Petersburg, A. S. Popov demonstrated the operation of his device, which was, in fact, the world's first radio receiver. May 7th was the birthday of radio.

Properties of electromagnetic waves

Modern radio engineering devices make it possible to carry out very demonstrative experiments on observing the properties of electromagnetic waves. In this case, it is best to use the waves of the centimeter range. These waves are emitted by a special microwave generator. The electrical oscillations of the generator modulate the sound frequency. The received signal after detection is fed to the loudspeaker.

I will not describe the conduct of all experiments, but will focus on the main ones.

1. Dielectrics are capable of absorbing electromagnetic waves.

2. Some substances (for example, metal) are capable of absorbing electromagnetic waves.

3. Electromagnetic waves are capable of changing their direction at the dielectric boundary.

4. Electromagnetic waves are transverse waves. This means that the vectors E and B of the electromagnetic field of the wave are perpendicular to the direction of its propagation.

Modulation and detection

Since the invention of radio by Popov, some time has passed when people wanted to transmit speech and music instead of telegraph signals, consisting of short and long signals. This is how radiotelephony was invented. Consider the basic principles of the operation of such a connection.

In radiotelephone communications, air pressure fluctuations in a sound wave are converted by a microphone into electrical vibrations the same shape. It would seem that if these vibrations are amplified and fed into the antenna, then it will be possible to transmit speech and music over a distance using electromagnetic waves. However, in reality, such a method of transmission is not feasible. The fact is that vibrations of sound of a new frequency are relatively slow vibrations, and electromagnetic waves of low (sound) frequency are almost not emitted at all. To overcome this obstacle, modulation and detection were developed, let's consider them in detail.

Modulation. To carry out radiotelephone communication, it is necessary to use high-frequency vibrations intensely radiated by the antenna. Continuous high-frequency harmonic oscillations are generated by an oscillator, such as a transistor oscillator.

To transmit sound, these high-frequency vibrations are modified, or as they say, modulated, with the help of electrical vibrations of low (sound) frequency. It is possible, for example, to change the amplitude of high-frequency oscillations with sound frequency. This method is called amplitude modulation.

a graph of high frequency oscillations, which is called the carrier frequency;

b) a graph of sound frequency oscillations, i.e., modulating oscillations;

c) a graph of amplitude-modulated oscillations.

Without modulation, at best, we can control whether the station is working or silent. Without modulation, there is no telegraph, telephone, or television transmission.

Amplitude modulation of high-frequency oscillations is achieved by a special effect on the generator of continuous oscillations. In particular, modulation can be carried out by changing the voltage created by the source on the oscillatory circuit. The greater the voltage on the generator circuit, the more energy is supplied per period from the source to the circuit. This leads to an increase in the amplitude of oscillations in the circuit. When the voltage decreases, the energy entering the circuit also decreases. Therefore, the amplitude of oscillations in the circuit also decreases.

In the simplest device for amplitude modulation, they are connected in series with a constant voltage source additional source alternating voltage of low frequency. This source can be, for example, the secondary winding of a transformer, if an audio frequency current flows through its primary winding. As a result, the amplitude of oscillations in the oscillatory circuit of the generator will change in time with changes in the voltage across the transistor. This means that high-frequency oscillations are modulated in amplitude by a low-frequency signal.

In addition to amplitude modulation, in some cases frequency modulation is used - a change in the oscillation frequency in accordance with the control signal. Its advantage is greater resistance to interference.

Detection. In the receiver, low-frequency oscillations are distinguished from the modulated high-frequency oscillations. This signal conversion process is called detection.

The signal obtained as a result of detection corresponds to the sound signal that acted on the transmitter microphone. After amplification, low frequency vibrations can be turned into sound.

The modulated high-frequency signal received by the receiver, even after amplification, is not capable of directly causing oscillations of the telephone membrane or the horn of the loudspeaker with an audio frequency. It can only cause high-frequency vibrations that are not perceived by our ear. Therefore, in the receiver, it is first necessary to isolate the audio frequency signal from high-frequency modulated oscillations.

Detection is carried out by a device containing an element with one-way conduction - a detector. Such an element can be a vacuum tube (vacuum diode) or a semiconductor diode.

Consider the operation of a semiconductor detector. Let this device be connected in series with the source of modulated oscillations and the load. The current in the circuit will flow predominantly in one direction.

A pulsating current will flow in the circuit. This pulsating current is smoothed out by a filter. The simplest filter is a capacitor connected to a load.

The filter works like this. At those moments in time when the diode passes current, part of it passes through the load, and the other part branches into the capacitor, charging it. Current splitting reduces the ripple of the current passing through the load. But in the interval between pulses, when the diode is locked, the capacitor is partially discharged through the load.

Therefore, in the interval between pulses, the current flows through the load in the same direction. Each new pulse recharges the capacitor. As a result, an audio-frequency current flows through the load, the waveform of which almost exactly reproduces the waveform of the low-frequency signal at the transmitting station.

Types of radio waves and their propagation

We have already considered the basic properties of electromagnetic waves, their application in radio, the formation of radio waves. Now let's get acquainted with the types of radio waves and their propagation.

The shape and physical properties of the earth's surface, as well as the state of the atmosphere, greatly affect the propagation of radio waves.

Layers of ionized gas in the upper parts of the atmosphere at an altitude of 100-300 km above the Earth's surface have a particularly significant effect on the propagation of radio waves. These layers are called the ionosphere. The ionization of the air of the upper layers of the atmosphere is caused by the electromagnetic radiation of the Sun and the flow of charged particles emitted by it.

The electrically conductive ionosphere reflects radio waves with a wavelength > 10 m, like an ordinary metal plate. But the ability of the ionosphere to reflect and absorb radio waves varies significantly depending on the time of day and seasons.

Stable radio communication between remote points on the earth's surface outside the line of sight is possible due to the reflection of waves from the ionosphere and the ability of radio waves to bend around the convex earth's surface. This bending is more pronounced, the longer the wavelength. Therefore, radio communication over long distances due to wave bending around the Earth is possible only at wavelengths significantly exceeding 100 m ( medium and long waves)

short waves(wavelength range from 10 to 100 m) propagate over long distances only due to multiple reflections from the ionosphere and the Earth's surface. It is with the help of short waves that radio communication can be carried out at any distance between radio stations on Earth.

ultrashort radio waves (λ <10 м) проникают сквозь ионосферу и почти не огибают поверхность Земли. Поэтому они используются для радиосвязи между пунктами в пределах прямой видимости, а также для связи с космическими кораб­лями.

Now consider another application of radio waves. This is radar.

The detection and precise location of objects using radio waves is called radar. Radar installation - radar(or radar) - consists of transmitting and receiving parts. Radar uses ultra-high frequency electrical vibrations. A powerful microwave generator is connected to an antenna that emits a highly directional wave. The sharp directivity of the radiation is obtained due to the addition of waves. The antenna is designed so that the waves sent by each of the vibrators, when added, mutually reinforce each other only in a given direction. In other directions, when the waves are added, their complete or partial mutual damping occurs.

The reflected wave is captured by the same transmitting antenna or by another, also highly directional receiving antenna.

To determine the distance to the target, a pulsed radiation mode is used. The transmitter emits waves in short pulses. The duration of each pulse is millionths of a second, and the interval between pulses is about 1000 times longer. During pauses, reflected waves are received.

Distance is determined by measuring the total travel time of radio waves to and from the target. Since the speed of radio waves c \u003d 3 * 10 8 m / s in the atmosphere is practically constant, then R \u003d ct / 2.

To fix the sent and reflected signals, a cathode ray tube is used.

Radio waves are used not only to transmit sound, but also to transmit images (television).

The principle of transmitting images over a distance is as follows. At the transmitting station, the image is converted into a sequence of electrical signals. These signals then modulate the oscillations generated by the high frequency generator. A modulated electromagnetic wave carries information over long distances. The receiver performs the reverse conversion. High-frequency modulated oscillations are detected and the received signal is converted into a visible image. To convey movement, the principle of cinema is used: slightly different images of a moving object (frames) are transmitted dozens of times per second (50 times in our television).

The image of the frame is converted by a transmitting vacuum electron tube - an iconoscope into a series of electrical signals. In addition to the iconoscope, there are other transmitting devices. Inside the iconoscope there is a mosaic screen onto which an image of the object is projected with the help of an optical system. Each cell of the mosaic is charged, and its charge depends on the intensity of the light falling on the cell. This charge changes when the electron beam produced by the electron gun hits the cell. The electron beam sequentially hits all elements, first of one line of the mosaic, then another line, etc. (625 lines in total).

How much the charge of the cell changes depends on the current strength in the resistor R. Therefore, the voltage across the resistor changes in proportion to the change in illumination along the lines of the frame.

The same signal is obtained in the television receiver after detection. it video signal. It is converted into a visible image on the screen of the receiving vacuum electron tube - kinescope.

Television radio signals can only be transmitted in the range of ultrashort (meter) waves.

Bibliography.

1. Myakishev G.Ya. , Bukhovtsev B.B. Physics - 11. M. 1993.

2. Telesnin R.V., Yakovlev V.F. Physics course. Electricity. M. 1970

3. Yavorsky B.M., Pinsky A.A. Fundamentals of physics. v. 2. M. 1981

Vladimir Regional Industrial and Commercial Lyceum abstract topic: Electromagnetic waves

Electromagnetic waves (the table of which will be given below) are perturbations of magnetic and electric fields that are distributed in space. There are several types of them. Physics is the study of these perturbations. Electromagnetic waves are formed due to the fact that an electric alternating field generates a magnetic one, and this, in turn, generates an electric one.

Research history

The first theories, which can be considered the oldest versions of the hypotheses about electromagnetic waves, date back at least to the times of Huygens. In that period, the assumptions reached a pronounced quantitative development. Huygens in 1678 published a kind of "outline" of the theory - "Treatise on Light". In 1690, he also published another remarkable work. It outlined the qualitative theory of reflection, refraction in the form in which it is still presented in school textbooks ("Electromagnetic waves", grade 9).

At the same time, Huygens' principle was formulated. With its help, it became possible to study the motion of the wave front. This principle was subsequently developed in the works of Fresnel. The Huygens-Fresnel principle was of particular importance in the theory of diffraction and the wave theory of light.

In the 1660s-1670s, Hooke and Newton made a great experimental and theoretical contribution to research. Who discovered electromagnetic waves? Who conducted the experiments proving their existence? What are the types of electromagnetic waves? More on this later.

Maxwell's justification

Before talking about who discovered electromagnetic waves, it should be said that the first scientist who predicted their existence at all was Faraday. He put forward his hypothesis in 1832. The theory was later developed by Maxwell. By 1865 he completed this work. As a result, Maxwell formalized the theory strictly mathematically, substantiating the existence of the phenomena under consideration. He also determined the speed of propagation of electromagnetic waves, which coincided with the then used value of the speed of light. This, in turn, allowed him to substantiate the hypothesis that light is one of the types of radiation under consideration.

Experimental discovery

Maxwell's theory found its confirmation in the experiments of Hertz in 1888. Here it should be said that the German physicist carried out his experiments in order to disprove the theory, despite its mathematical justification. However, thanks to his experiments, Hertz became the first to discover electromagnetic waves in practice. In addition, during his experiments, the scientist revealed the properties and characteristics of radiation.

Hertz obtained electromagnetic oscillations and waves by excitation of a series of pulses of a rapidly changing flow in a vibrator using an increased voltage source. High frequency streams can be detected using a loop. In this case, the oscillation frequency will be the higher, the higher its capacitance and inductance. But at the same time, a high frequency is not a guarantee of an intense flow. To conduct his experiments, Hertz used a fairly simple device, which today is called the “Hertz vibrator”. The device is an open-type oscillatory circuit.

Diagram of Hertz's experience

Registration of radiation was carried out using a receiving vibrator. This device had the same design as the radiating device. Under the influence of an electromagnetic wave of an electric alternating field, a current oscillation was excited in the receiving device. If in this device its natural frequency and the frequency of the flow coincided, then a resonance appeared. As a result, disturbances in the receiving device occurred with a larger amplitude. The researcher discovered them by observing the sparks between the conductors in a small gap.

Thus, Hertz became the first who discovered electromagnetic waves, proved their ability to be well reflected from conductors. He practically substantiated the formation of standing radiation. In addition, Hertz determined the propagation speed of electromagnetic waves in the air.

Characteristics study

Electromagnetic waves propagate in almost all media. In a space that is filled with matter, radiation can in some cases be distributed fairly well. But at the same time they change their behavior somewhat.

Electromagnetic waves in vacuum are determined without attenuation. They are distributed over any, arbitrarily large distance. The main characteristics of waves include polarization, frequency and length. The description of properties is carried out within the framework of electrodynamics. However, more specific branches of physics deal with the characteristics of radiation in certain regions of the spectrum. These include, for example, optics.

The high-energy section deals with the study of hard electromagnetic radiation of the short-wavelength spectral end. Taking into account modern ideas, dynamics ceases to be an independent discipline and is combined with in one theory.

Theories applied in the study of properties

Today, there are various methods that contribute to the modeling and study of the manifestations and properties of vibrations. The most fundamental of the proven and completed theories is quantum electrodynamics. From it, through certain simplifications, it becomes possible to obtain the following methods, which are widely used in various fields.

The description of relatively low-frequency radiation in a macroscopic medium is carried out using classical electrodynamics. It is based on Maxwell's equations. At the same time, there are simplifications in applied applications. An optical study uses optics. Wave theory is used in cases where some parts of the optical system are close in size to wavelengths. Quantum optics is used when the processes of scattering and absorption of photons are essential.

Geometric optical theory is the limiting case in which the wavelength is allowed to be neglected. There are also several applied and fundamental sections. These include, for example, astrophysics, the biology of visual perception and photosynthesis, and photochemistry. How are electromagnetic waves classified? A table illustrating the distribution into groups is presented below.

Classification

There are frequency ranges of electromagnetic waves. There are no sharp transitions between them, sometimes they overlap each other. The boundaries between them are rather arbitrary. Due to the fact that the flow is distributed continuously, the frequency is rigidly associated with the length. Below are the ranges of electromagnetic waves.

Ultrashort radiation is usually divided into micrometer (submillimeter), millimeter, centimeter, decimeter, meter. If the electromagnetic radiation is less than a meter, then it is commonly called an ultra-high frequency oscillation (SHF).

Types of electromagnetic waves

Above are the ranges of electromagnetic waves. What are the types of streams? The group includes gamma and x-rays. At the same time, it should be said that both ultraviolet and even visible light are capable of ionizing atoms. The boundaries within which gamma and x-ray fluxes are located are determined rather conditionally. The limits of 20 eV - 0.1 MeV are accepted as a general orientation. Gamma fluxes in the narrow sense are emitted by the nucleus, X-rays are emitted by the electron atomic shell in the process of knocking out electrons from low-lying orbits. However, this classification is not applicable to hard radiation generated without the participation of nuclei and atoms.

X-ray streams are formed when charged fast particles (protons, electrons, etc.) slow down and as a result of processes that occur inside atomic electron shells. Gamma oscillations arise as a result of processes inside the nuclei of atoms and during the transformation of elementary particles.

radio streams

Due to the large value of the lengths, these waves can be considered without taking into account the atomistic structure of the medium. The only exceptions are the shortest streams, which are adjacent to the infrared region of the spectrum. In the radio range, the quantum properties of oscillations manifest themselves rather weakly. Nevertheless, they must be taken into account, for example, when analyzing molecular time and frequency standards during equipment cooling to a temperature of several kelvins.

Quantum properties are also taken into account when describing oscillators and amplifiers in the millimeter and centimeter ranges. The radio stream is formed during the movement of alternating current through the conductors of the corresponding frequency. A passing electromagnetic wave in space excites the corresponding wave. This property is used in the design of antennas in radio engineering.

Visible streams

Ultraviolet and infrared visible radiation in the broad sense of the word is the so-called optical part of the spectrum. The selection of this region is determined not only by the proximity of the corresponding zones, but also by the similarity of the instruments used in the study and developed mainly during the study of visible light. These include, in particular, mirrors and lenses for focusing radiation, diffraction gratings, prisms, and others.

The frequencies of optical waves are comparable with those of molecules and atoms, and their lengths are comparable with intermolecular distances and molecular sizes. Therefore, phenomena that are due to the atomistic structure of matter become significant in this area. For the same reason, light, along with wave properties, also has quantum properties.

The emergence of optical flows

The most famous source is the Sun. The surface of the star (photosphere) has a temperature of 6000 Kelvin and emits bright white light. The highest value of the continuous spectrum is located in the "green" zone - 550 nm. There is also a maximum of visual sensitivity. Oscillations in the optical range occur when bodies are heated. Infrared flows are therefore also referred to as thermal.

The stronger the heating of the body, the higher the frequency, where the maximum of the spectrum is located. With a certain increase in temperature, heat is observed (glow in the visible range). In this case, red color appears first, then yellow and so on. The creation and registration of optical flows can occur in biological and chemical reactions, one of which is used in photography. For most creatures living on Earth, photosynthesis acts as a source of energy. This biological reaction takes place in plants under the influence of optical solar radiation.

Features of electromagnetic waves

The properties of the medium and the source influence the characteristics of the flows. This establishes, in particular, the time dependence of the fields, which determines the type of flow. For example, when the distance from the vibrator changes (as it increases), the radius of curvature becomes larger. As a result, a plane electromagnetic wave is formed. Interaction with matter also occurs in different ways.

The processes of absorption and emission of flows, as a rule, can be described using classical electrodynamic relations. For waves in the optical region and for hard rays, all the more so, their quantum nature should be taken into account.

Stream Sources

Despite the physical difference, everywhere - in a radioactive substance, a television transmitter, an incandescent lamp - electromagnetic waves are excited by electric charges that move with acceleration. There are two main types of sources: microscopic and macroscopic. In the first, there is an abrupt transition of charged particles from one to another level inside molecules or atoms.

Microscopic sources emit X-ray, gamma, ultraviolet, infrared, visible, and in some cases long-wave radiation. An example of the latter is the line in the spectrum of hydrogen, which corresponds to a wave of 21 cm. This phenomenon is of particular importance in radio astronomy.

Macroscopic sources are emitters in which free electrons of conductors perform periodic synchronous oscillations. In systems of this category, flows are generated from millimeter to the longest (in power lines).

Structure and strength of flows

With acceleration and periodically changing currents affect each other with certain forces. The direction and their magnitude are dependent on such factors as the size and configuration of the area in which the currents and charges are contained, their relative direction and magnitude. The electrical characteristics of a particular medium, as well as changes in the concentration of charges and the distribution of source currents, also have a significant effect.

Due to the general complexity of the problem statement, it is impossible to represent the law of forces in the form of a single formula. The structure, called the electromagnetic field, and considered, if necessary, as a mathematical object, is determined by the distribution of charges and currents. It, in turn, is created by a given source, taking into account the boundary conditions. The conditions are determined by the shape of the interaction zone and the characteristics of the material. If we are talking about unlimited space, these circumstances are supplemented. In such cases, the radiation condition acts as a special additional condition. Due to it, the "correct" behavior of the field at infinity is guaranteed.

Timeline of study

Lomonosov in some of his provisions anticipates certain postulates of the theory of the electromagnetic field: "rotary" (rotational) motion of particles, "fluctuating" (wave) theory of light, its commonality with the nature of electricity, etc. Infrared streams were discovered in 1800 by Herschel (English scientists), and in the next, 1801, ultraviolet was described by Ritter. Radiation shorter than ultraviolet range was discovered by Roentgen in 1895, November 8th. Subsequently, it was called X-ray.

The influence of electromagnetic waves has been studied by many scientists. However, Narkevich-Iodko (Belarusian scientist) was the first to explore the possibilities of flows and their scope. He studied the properties of flows in relation to practical medicine. Gamma radiation was discovered by Paul Willard in 1900. During the same period, Planck conducted theoretical studies of the properties of a black body. In the process of studying, he discovered the quantum nature of the process. His work was the beginning of development Subsequently, several works by Planck and Einstein were published. Their research led to the formation of such a concept as a photon. This, in turn, marked the beginning of the creation of the quantum theory of electromagnetic flows. Its development continued in the works of leading scientists of the twentieth century.

Further research and work on the quantum theory of electromagnetic radiation and its interaction with matter eventually led to the formation of quantum electrodynamics in the form in which it exists today. Among the outstanding scientists involved in the study of this issue, it should be mentioned, in addition to Einstein and Planck, Bohr, Bose, Dirac, de Broglie, Heisenberg, Tomonaga, Schwinger, Feynman.

Conclusion

The importance of physics in the modern world is quite large. Almost everything that is used today in human life has appeared thanks to the practical use of the research of great scientists. The discovery of electromagnetic waves and their study, in particular, led to the creation of conventional, and later mobile phones, radio transmitters. The practical application of such theoretical knowledge is of particular importance in the field of medicine, industry, and technology.

This widespread use is due to the quantitative nature of science. All physical experiments are based on measurements, comparison of the properties of the studied phenomena with the available standards. It is for this purpose that a complex of measuring instruments and units has been developed within the framework of the discipline. A number of regularities is common to all existing material systems. For example, the laws of conservation of energy are considered general physical laws.

Science as a whole is called in many cases fundamental. This is primarily due to the fact that other disciplines give descriptions, which, in turn, obey the laws of physics. So, in chemistry, atoms, substances formed from them, and transformations are studied. But the chemical properties of bodies are determined by the physical characteristics of molecules and atoms. These properties describe such branches of physics as electromagnetism, thermodynamics and others.

Electromagnetic waves, according to physics, are among the most mysterious. In them, the energy actually disappears into nowhere, appears from nowhere. There is no other similar object in all of science. How do all these miraculous transformations take place?

Maxwell electrodynamics

It all started with the fact that the scientist Maxwell back in 1865, relying on the work of Faraday, derived the equation of the electromagnetic field. Maxwell himself believed that his equations described the torsion and tension of waves in the ether. Twenty-three years later, Hertz experimentally created such perturbations in the medium, and succeeded not only in reconciling them with the equations of electrodynamics, but also in obtaining the laws governing the propagation of these perturbations. A curious tendency has arisen to declare any perturbations that are electromagnetic in nature as Hertzian waves. However, these radiations are not the only way to carry out energy transfer.

Wireless connection

To date, possible options for the implementation of such wireless communications include:

Electrostatic coupling, also called capacitive;

induction;

current;

Tesla connection, that is, the connection of electron density waves along conductive surfaces;

The widest range of the most common carriers, which are called electromagnetic waves - from ultra-low frequencies to gamma radiation.

It is worth considering these types of connections in more detail.

Electrostatic bond

The two dipoles are coupled electrical forces in space, which is a consequence of Coulomb's law. This type of connection differs from electromagnetic waves by the ability to connect dipoles when they are located on the same line. With increasing distances, the strength of the connection attenuates, and a strong influence of various interferences is also observed.

inductive coupling

Based on magnetic stray fields of inductance. Observed between objects that have inductance. Its application is quite limited due to short-range action.

Current connection

Due to the spreading currents in a conducting medium, a certain interaction can occur. If currents are passed through the terminals (a pair of contacts), then these same currents can be detected at a considerable distance from the contacts. This is what is called the effect of current spreading.

Tesla connection

The famous physicist Nikola Tesla invented communication using waves on a conductive surface. If in some place of the plane the density of the charge carrier is disturbed, then these carriers will begin to move, which will tend to restore equilibrium. Since the carriers have an inertial nature, the recovery has a wave character.

Electromagnetic connection

The radiation of electromagnetic waves is distinguished by a huge long-range action, since their amplitude is inversely proportional to the distance to the source. It is this method of wireless communication that is most widely used. But what are electromagnetic waves? First you need to make a short digression into the history of their discovery.

How did electromagnetic waves "appear"?

It all started in 1829, when the American physicist Henry discovered perturbations in electrical discharges in experiments with Leyden jars. In 1832, the physicist Faraday suggested the existence of such a process as electromagnetic waves. Maxwell created his famous equations of electromagnetism in 1865. At the end of the nineteenth century, there were many successful attempts to create wireless communication using electrostatic and electromagnetic induction. The famous inventor Edison came up with a system that allowed railroad passengers to send and receive telegrams while the train was moving. In 1888, G. Hertz unequivocally proved that electromagnetic waves appear using a device called a vibrator. Hertz carried out an experiment on the transmission of an electromagnetic signal over a distance. In 1890, French engineer and physicist Branly invented a device for recording electromagnetic radiation. Subsequently, this device was called the "radio conductor" (coherer). In 1891-1893, Nikola Tesla described the basic principles for the implementation of signal transmission over long distances and patented a mast antenna, which was a source of electromagnetic waves. Further merits in the study of waves and the technical implementation of their production and application belong to such famous physicists and inventors as Popov, Marconi, de Maur, Lodge, Mirhead and many others.

The concept of "electromagnetic wave"

An electromagnetic wave is a phenomenon that propagates in space with a certain finite speed and is an alternating electric and magnetic field. Since magnetic and electric fields are inextricably linked with each other, they form an electromagnetic field. It can also be said that an electromagnetic wave is a perturbation of the field, and during its propagation, the energy that the magnetic field has is converted into the energy of the electric field and vice versa, according to Maxwell's electrodynamics. Outwardly, this is similar to the propagation of any other wave in any other medium, but there are also significant differences.

What is the difference between electromagnetic waves and others?

The energy of electromagnetic waves propagates in a rather incomprehensible medium. To compare these waves and any others, it is necessary to understand what kind of propagation medium we are talking about. It is assumed that the intra-atomic space is filled with electric ether - a specific medium, which is an absolute dielectric. All waves during propagation show the transition of kinetic energy into potential energy and vice versa. At the same time, the maximum of these energies is shifted in time and space relative to each other by one fourth of the total period of the wave. In this case, the average wave energy, being the sum of potential and kinetic energy, is a constant value. But with electromagnetic waves, the situation is different. The energies of both the magnetic and electric fields reach their maximum values ​​simultaneously.

How is an electromagnetic wave generated?

The matter of an electromagnetic wave is an electric field (ether). The moving field is structured and consists of the energy of its movement and the electric energy of the field itself. Therefore, the potential energy of the wave is related to the kinetic energy and is in phase. The nature of an electromagnetic wave is a periodic electric field that is in a state of translational motion in space and moves at the speed of light.

Displacement currents

There is another way to explain what electromagnetic waves are. It is assumed that displacement currents arise in the ether during the movement of inhomogeneous electric fields. They arise, of course, only for a stationary outside observer. At the moment when such a parameter as the electric field strength reaches its maximum, the displacement current at a given point in space will stop. Accordingly, at a minimum of tension, the reverse picture is obtained. This approach clarifies the wave nature of electromagnetic radiation, since the energy of the electric field turns out to be shifted by one fourth of the period with respect to displacement currents. Then we can say that the electrical disturbance, or rather the energy of the disturbance, is transformed into the energy of the displacement current and vice versa and propagates in a wave manner in a dielectric medium.

electromagnetic waves called the process of propagation in space of an alternating electromagnetic field. Theoretically, the existence of electromagnetic waves was predicted by the English scientist Maxwell in 1865, and they were first experimentally obtained by the German scientist Hertz in 1888.

Formulas describing the oscillations of the vectors and follow from Maxwell's theory. Plane monochromatic electromagnetic wave propagating along the axis x, is described by the equations

Here E and H are instantaneous values, and E m and H m - amplitude values ​​of electric and magnetic fields, ω - circular frequency, k- wave number. The vectors and oscillate with the same frequency and phase, are mutually perpendicular and, in addition, are perpendicular to the vector - the speed of wave propagation (Fig. 3.7). That is, electromagnetic waves are transverse.

In a vacuum, electromagnetic waves propagate with speed. In a medium with permittivity ε and magnetic permeability µ the propagation speed of an electromagnetic wave is:

The frequency of electromagnetic oscillations, as well as the wavelength, can in principle be any. The classification of waves by frequency (or wavelength) is called the scale of electromagnetic waves. Electromagnetic waves are divided into several types.

radio waves have a wavelength from 10 3 to 10 -4 m.

light waves include:

x-ray radiation - .

Light waves are electromagnetic waves that include infrared, visible and ultraviolet parts of the spectrum. The wavelengths of light in vacuum corresponding to the primary colors of the visible spectrum are shown in the table below. The wavelength is given in nanometers.

Table

Light waves have the same properties as electromagnetic waves.

1. Light waves are transverse.

2. Vectors u oscillate in a light wave.

Experience shows that all types of influences (physiological, photochemical, photoelectric, etc.) are caused by oscillations of the electric vector. He is called light vector .

Light vector amplitude E m is often denoted by the letter A and equation (3.24) is used instead of equation (3.30).

3. The speed of light in a vacuum.

The speed of a light wave in a medium is determined by formula (3.29). But for transparent media (glass, water) usually.

For light waves, a concept is introduced - the absolute refractive index.

Absolute refractive index is the ratio of the speed of light in a vacuum to the speed of light in a given medium

From (3.29), taking into account the fact that for transparent media , we can write the equality.

For vacuum ε = 1 and n= 1. For any physical environment n> 1. For example, for water n= 1.33, for glass. A medium with a higher refractive index is said to be optically denser. The ratio of absolute refractive indices is called relative refractive index:

4. The frequency of light waves is very high. For example, for red light with a wavelength.

When light passes from one medium to another, the frequency of light does not change, but the speed and wavelength change.

For vacuum - ; for environment - , then

Hence, the wavelength of light in a medium is equal to the ratio of the wavelength of light in vacuum to the refractive index

5. Because the frequency of light waves is very high , then the observer's eye does not distinguish between individual oscillations, but perceives averaged energy flows. Thus the concept of intensity is introduced.

intensity is the ratio of the average energy carried by the wave to the time interval and to the area of ​​the site perpendicular to the direction of wave propagation:

Since the wave energy is proportional to the square of the amplitude (see formula (3.25)), the intensity is proportional to the average value of the square of the amplitude

A characteristic of the intensity of light, taking into account its ability to cause visual sensations, is luminous flux - F .

6. The wave nature of light is manifested, for example, in such phenomena as interference and diffraction.