Every time an electric current changes its frequency or direction, it generates electromagnetic waves - oscillations of electric and magnetic force fields in space. One example is the changing current in the antenna of a radio transmitter, which creates rings of radio waves propagating in space.

The energy of an electromagnetic wave depends on its length - the distance between two adjacent “peaks”. The shorter the wavelength, the higher its energy. In descending order of their length, electromagnetic waves are divided into radio waves, infrared radiation, visible light, ultraviolet, x-rays and gamma radiation. The wavelength of gamma radiation does not reach even one hundred billionth of a meter, while radio waves can have a length measured in kilometers.

Electromagnetic waves propagate in space at the speed of light, and the lines of force of their electric and magnetic fields are located at right angles to each other and to the direction of motion of the wave.

Electromagnetic waves radiate out in gradually widening circles from the transmitting antenna of a two-way radio station, similar to the way waves do when a pebble falls into a pond. The alternating electric current in the antenna creates waves consisting of electric and magnetic fields.

Electromagnetic wave circuit

An electromagnetic wave travels in a straight line, and its electric and magnetic fields are perpendicular to the flow of energy.

Refraction of electromagnetic waves

Just like light, all electromagnetic waves are refracted when they enter matter at any angle other than right angles.

Reflection of electromagnetic waves

If electromagnetic waves fall on a metal parabolic surface, they are focused at a point.

The rise of electromagnetic waves

the false pattern of electromagnetic waves emanating from a transmitting antenna arises from a single oscillation of electrical current. When current flows up the antenna, the electric field (red lines) is directed from top to bottom, and the magnetic field (green lines) is directed counterclockwise. If the current changes its direction, the same happens to the electric and magnetic fields.

Vladimir regional
industrial - commercial
lyceum

abstract

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. Flux density of electromagnetic radiation……………. 7

6. Invention of radio…………………………………………….… 9

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

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

9. Types of radio waves and their distribution………………………… 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 require any substance to propagate, which includes 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 behave similarly to mechanical waves during their propagation. But like oscillations, all types of waves are described quantitatively by the same or almost identical laws. In my work I will try to consider the reasons for the occurrence of electromagnetic waves, their properties and application in our lives.

The concept of a wave and its characteristics

Wave are 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, movement is transmitted from one part of the body to another. Associated with the transfer of motion is the transfer of energy. The main property of all waves, regardless of their nature, is the transfer of anergy without the transfer of matter. The energy comes from a source that excites vibrations at the beginning of a cord, string, etc., and spreads along with the wave. Energy flows continuously through any cross section. This energy consists of the kinetic energy of movement of sections of the cord and the potential energy of its elastic deformation. The gradual decrease in the amplitude of oscillations as the wave propagates is associated with the conversion of part of the mechanical energy into internal energy.

If you make the end of a stretched rubber cord vibrate harmoniously with a certain frequency v, then these vibrations will begin to propagate along the cord. Vibrations of any section of the cord occur with the same frequency and amplitude as the vibrations 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 exactly the same: after all, cos(2lvt+2l) = =сos2пvt. Such oscillations are called in-phase(occur in the same phases).

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

Relationship between wavelength λ, frequency v and wave speed c. During one oscillation period, 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 the relation T = 1 / v

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

Electromagnetic waves

Now let's move on to considering electromagnetic waves directly.

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

Among the countless, very interesting and important consequences arising from Maxwell's laws of the electromagnetic field, one deserves special attention. This is the conclusion that 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, spreading, covers increasingly large areas of the surrounding space.

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

Imagine that an electric charge has not simply shifted from one point to another, but is set into rapid oscillations along a certain 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 at a greater distance from the charge, etc.

At each point in space, electric and magnetic fields change periodically in time. The further a point is located from the charge, the later the field oscillations reach it. Consequently, at different distances from the charge, oscillations occur with different phases.

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

An electromagnetic wave is transverse.

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

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 discovered? To answer this question, consider the experiments of Hertz.

An electromagnetic wave is formed due to the mutual connection of alternating electric and magnetic fields. Changing one field causes another to appear. As is known, the faster the magnetic induction changes over time, the greater the intensity of the resulting electric field. And in turn, the faster the electric field strength changes, the greater the magnetic induction.

To generate intense electromagnetic waves, it is necessary to create electromagnetic oscillations of a sufficiently high frequency.

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

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

This device is an open oscillatory circuit.

You can move to an open circuit from a closed circuit if you gradually move the capacitor plates 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 an 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 moment in 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 zero, and in the middle it reaches a maximum (in ordinary alternating current circuits, the current strength in all sections at a given moment in time is the same.) The electromagnetic field also covers the entire space near the circuit.

Hertz received electromagnetic waves by exciting a series of pulses of rapidly alternating current in a vibrator using a high voltage source. Oscillations of electric charges in a vibrator create an electromagnetic wave. Only the 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, vectors E and B are perpendicular to each other. Vector E lies in the plane passing through the vibrator, and vector B is perpendicular to this plane. The waves are emitted with maximum intensity in the direction perpendicular to the vibrator axis. No radiation occurs 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 influence 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 discovered 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 types 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 using the formula c = 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.

Electromagnetic radiation flux density

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

Consider a surface of area S through which electromagnetic waves transfer energy.

The flux density of electromagnetic radiation I is the ratio of the electromagnetic energy W passing during time t through a surface of area S perpendicular to the rays to the product of area S and time t.

Radiation flux density, in SI, is expressed in watts per square meter (W/m2). This quantity is sometimes called wave intensity.

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

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

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

A radiation source is considered point-like if its dimensions are much smaller than the distance at which its effect is assessed. 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 carried by electromagnetic waves 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. You can find out the dependence of the radiation flux density on the distance to the source by placing a point source at the center of a sphere with a radius R. surface area of ​​the sphere S= 4 n R^2. If we assume that the source emits energy W in all directions during time t

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

Now consider the dependence of the radiation flux density on frequency. As is known, the emission of electromagnetic waves occurs during the accelerated movement of charged particles. The electric field strength and magnetic induction of an electromagnetic wave are proportional to the acceleration A radiating particles. Acceleration during harmonic vibrations 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 frequency.

Invention of the radio

Hertz's experiments interested physicists around 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 “senses” electromagnetic waves. This device is a glass tube with two electrodes. The tube contains small metal filings. The operation of the device is based on the effect of electrical discharges on metal powders. Under normal conditions, the coherer has high resistance because the sawdust has poor contact with each other. The arriving 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. 100-200 times). 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 bell device to shake the coherer after receiving the signal. The electric bell circuit was closed using a sensitive relay at the moment the electromagnetic wave arrived. With the end of receiving the wave, the operation of the bell immediately stopped, since the bell hammer struck not only the bell cup, but also the coherer. With the last shaking 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 terminals 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 oscillating 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 produces very weak electromagnetic oscillations. As in A. S. Popov’s receiver, the energy of these oscillations is not used directly for reception. Weak signals only control the energy sources that power subsequent circuits. Nowadays such control is carried out using semiconductor devices.

On May 7, 1895, at a meeting of the Russian Physical-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 became the birthday of radio.

Properties of electromagnetic waves

Modern radio engineering devices make it possible to conduct very visual experiments to observe the properties of electromagnetic waves. In this case, it is best to use centimeter waves. These waves are emitted by a special ultra-high frequency (microwave) generator. The electrical oscillations of the generator are modulated by sound frequency. The received signal, after detection, is sent 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

Some time has passed since the invention of radio by Popov, when people wanted to transmit speech and music instead of telegraph signals consisting of short and long signals. This is how radiotelephone communication was invented. Let's consider the basic principles of how such a connection works.

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

Modulation. To carry out radiotelephone communication, it is necessary to use high-frequency oscillations intensively emitted by the antenna. Undamped harmonic oscillations of high frequency are produced by a generator, for example a transistor generator.

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

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

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

c) 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 special action on the generator of continuous oscillations. In particular, modulation can be accomplished by changing the voltage generated by the source on the oscillating circuit. The higher the voltage on the generator circuit, the more energy flows from the source into the circuit per period. This leads to an increase in the amplitude of oscillations in the circuit. As the voltage decreases, the energy entering the circuit also decreases. Therefore, the amplitude of oscillations in the circuit decreases.

In the simplest device for implementing amplitude modulation, an additional source of low-frequency alternating voltage is connected in series with a constant voltage source. This source can be, for example, the secondary winding of a transformer if 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 on 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 - changing the oscillation frequency in accordance with the control signal. Its advantage is its greater resistance to interference.

Detection. In the receiver, low-frequency oscillations are separated from 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. Once amplified, 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 vibrations in the membrane of a telephone or a loudspeaker horn with an audio frequency. It can only cause high-frequency vibrations that are not perceived by our ears. Therefore, in the receiver it is first necessary to isolate an audio frequency signal from high-frequency modulated oscillations.

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

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

A pulsating current will flow in the circuit. This ripple current is smoothed out using a filter. The simplest filter is a capacitor connected to the 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 fanout reduces the ripple current passing through the load. But in the interval between pulses, when the diode is closed, 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 shape of the low-frequency signal at the transmitting station.

Types of radio waves and their distribution

We have already examined the basic properties of electromagnetic waves, their application in radio, and 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 influence 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 influence on the propagation of radio waves. These layers are called the ionosphere. Ionization of the air in the upper layers of the atmosphere is caused by electromagnetic radiation from the Sun and the flow of charged particles emitted by it.

Conducting electrical current, the ionosphere reflects radio waves with a wavelength > 10 m, like a regular 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 beyond 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 the waves bending around the Earth is possible only with 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 let's look at another application of radio waves. This is radar.

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 oscillations. A powerful microwave generator is connected to an antenna, which emits a highly directional wave. The sharp directionality of the radiation is obtained due to the addition of waves. The antenna is designed in such a way that the waves sent by each of the vibrators, when added, mutually reinforce each other only in a given direction. In other directions, when waves are added, their complete or partial mutual cancellation occurs.

The reflected wave is captured by the same emitting antenna or 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 bursts. The duration of each pulse is millionths of a second, and the interval between pulses is approximately 1000 times longer. During pauses, reflected waves are received.

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

A cathode ray tube is used to record the sent and reflected signals.

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 are then modulated by oscillations generated by a high-frequency generator. A modulated electromagnetic wave carries information over long distances. The reverse conversion is performed at the receiver. High frequency modulated oscillations are detected and the resulting signal is converted into a visible image. To transmit motion, they use the principle of cinema: slightly different images of a moving object (frames) are transmitted dozens of times per second (in our television 50 times).

The frame image is converted using 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 on which an image of the object is projected using an optical system. Each mosaic cell is charged, and its charge depends on the intensity of the light incident on the cell. This charge changes when an electron beam generated by an electron gun hits the cell. The electron beam sequentially hits all the elements of first one line of the mosaic, then another line, etc. (625 lines in total).

The current in the resistor depends on how much the cell charge changes. 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 received in the television receiver after detection. This 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 ultrashort (meter) wave range.

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. vol. 2. M. 1981

General concepts about electromagnetic waves

In today's lesson we will consider such a necessary topic as electromagnetic waves. And this topic is important, if only because our entire modern life is connected with television, radio broadcasting and mobile communications. Therefore, it is worth emphasizing that all this is carried out due to electromagnetic waves.

Now let's move on to a more detailed consideration of the issue related to electromagnetic waves and, first of all, we will voice the definition of such waves.

As you already know, a wave is a disturbance propagating in space, that is, if some disturbance has occurred somewhere and it spreads in all directions, then we can say that the spread of this disturbance is nothing more than a wave phenomenon.

Electromagnetic waves are electromagnetic oscillations that propagate in space with a finite speed, which depends on the properties of the medium. In other words, we can say that an electromagnetic wave is an electromagnetic field or electromagnetic disturbance propagating in space.

Let's start our discussion with the fact that the theory of electromagnetic waves of the electromagnetic field was first created by the English scientist James Maxwell. The most interesting and curious thing about this work is that it turns out that electric and magnetic fields, as you know, and since they have been proven to exist together. But it turns out that they can exist completely in the absence of any substance. This very important conclusion was made in the works of James Clerk Maxwell.

It turns out that an electromagnetic field can exist even where there is no substance. We told you that sound waves are present only where there is a medium. That is, the vibrations that occur with particles have the ability to be transmitted only where there are particles that have the ability to transmit this disturbance.

But as for the electromagnetic field, it can exist where there is no substance and there are no particles. And so, the electromagnetic field exists in a vacuum, which means it follows that if we create certain conditions and can, as it were, create a general electromagnetic disturbance in space, then accordingly this disturbance has the ability to spread in all directions. And this is exactly what we will have an electromagnetic wave.

The first person who was able to emit an electromagnetic wave and receive an electromagnetic wave was the German scientist Heinrich Hertz. He was the first to create such an installation for the radiation and reception of electromagnetic waves.

The first thing we must say here is that to emit an electromagnetic wave we need, of course, a fairly fast moving electric charge. We must create a device where there will be a very fast moving or accelerated moving electric charge.

Heinrich Hertz, with the help of his experiments, proved that in order to obtain a powerful and quite noticeable electromagnetic wave, a moving electric charge must oscillate at a very high frequency, that is, on the order of several tens of thousands of hertz. It should also be emphasized that if such an oscillation occurs at the charge, then an alternating electromagnetic field will be generated around it and spread in all directions. That is, this will be an electromagnetic wave.

Properties of electromagnetic waves

It is also necessary to note the fact that an electromagnetic wave, of course, has certain properties, and these properties were precisely indicated in the works of Maxwell.

It should also be noted that the properties of electromagnetic waves have certain differences, and also very much depend on its length. Depending on the properties and wavelength, electromagnetic waves are divided into ranges. They have a rather arbitrary scale, since adjacent ranges tend to overlap each other.

It is also useful to know that some areas have common properties. These properties include:

Penetration ability;
high speed of propagation in matter;
influence on the human body, both positive and negative, etc.

The types of electromagnetic waves include radio waves, ultraviolet and infrared ranges, visible light, as well as X-rays, gamma radiation and others.

Now let's carefully look at the table below and study in more detail how electromagnetic waves can be classified, what types of radiation there are, sources of radiation, as well as their frequency:

Interesting facts about electromagnetic waves

It will probably not be a secret to anyone that the space that surrounds us is permeated with electromagnetic radiation. Such radiation is associated not only with telephone and radio antennas, but also with the bodies around us, the Earth, the Sun and the stars. Depending on the frequency of oscillation, electromagnetic waves may have different names, but their essence is similar. Such electromagnetic waves include radio waves, infrared radiation, visible light, X-rays, as well as biofield rays.

Such a limitless source of energy as an electromagnetic field causes fluctuations in the electrical charges of atoms and molecules. It follows from this that when oscillating, the charge moves with acceleration and at the same time emits electromagnetic waves.

Impact of electromagnetic waves on human health

For many years, scientists have been concerned about the problem of the influence of electromagnetic fields on the health of humans, animals and plants and therefore devote a lot of time to research and study of this problem.

Probably, each of you has been to discos and noticed that under the influence of ultraviolet lamps, light-colored clothes began to glow. This type of radiation does not pose a danger to living organisms.

But when visiting a solarium or using ultraviolet lamps for medical purposes, it is necessary to use eye protection, since such exposure can cause short-term loss of vision.

Also, when using ultraviolet bactericidal lamps, which are used to disinfect premises, you must be extremely careful and when using them you must leave the room, as they negatively affect human skin, as well as plants, causing leaf burns.

But in addition to the radiation sources and various devices around us, the human body also has its own electric and magnetic fields. But you should also know that in the human body, throughout its life, electromagnetic fields tend to constantly change.

To determine the electromagnetic field of a person, such a precise device as an encephalograph is used. Using this device, you can accurately measure a person’s electromagnetic field and determine its activity in the cerebral cortex. Thanks to the advent of such a device as the encephalograph, it became possible to diagnose various diseases even at an early stage.

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

History of research

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

At the same time, Huygens' principle was formulated. With its help, it became possible to study the movement of the wave front. This principle subsequently found its development 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 and 1670s, Hooke and Newton made major experimental and theoretical contributions to research. Who discovered electromagnetic waves? Who conducted the experiments to prove their existence? What types of electromagnetic waves are there? More on this later.

Maxwell's Rationale

Before talking about who discovered electromagnetic waves, it should be said that the first scientist who generally predicted their existence was Faraday. He put forward his hypothesis in 1832. Maxwell subsequently worked on the construction of the theory. By 1865 he completed this work. As a result, Maxwell strictly formulated the theory mathematically, justifying 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 detection

Maxwell's theory was confirmed by Hertz's experiments in 1888. It should be said here that the German physicist conducted his experiments to disprove the theory, despite its mathematical justification. However, thanks to his experiments, Hertz became the first to practically discover electromagnetic waves. In addition, during his experiments, the scientist identified the properties and characteristics of radiation.

Hertz obtained electromagnetic oscillations and waves by exciting a series of pulses of a rapidly varying flow in a vibrator using a high voltage source. High frequency currents can be detected using a circuit. The higher the capacitance and inductance, the higher the oscillation frequency will be. But at the same time, a high frequency does not guarantee an intense flow. To carry out his experiments, Hertz used a fairly simple device, which today is called the “Hertz vibrator.” The device is an open type oscillating circuit.

Schematic of Hertz's experiment

Registration of radiation was carried out using a receiving vibrator. This device had the same design as the emitting 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 resonance appeared. As a result, disturbances in the receiving device occurred with greater amplitude. The researcher discovered them by observing sparks between the conductors in a small gap.

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

Characteristics Study

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

Electromagnetic waves in a vacuum are detected without attenuation. They are distributed over any, no matter how large, distance. The main characteristics of waves include polarization, frequency and length. The properties are described 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 study of hard electromagnetic radiation at the short-wave spectral end is carried out by the high-energy section. Taking into account modern ideas, dynamics ceases to be an independent discipline and is combined with one theory.

Theories used in the study of properties

Today, there are various methods that facilitate the modeling and study of the manifestations and properties of oscillations. Quantum electrodynamics is considered the most fundamental of the tested and completed theories. From it, through certain simplifications, it becomes possible to obtain the methods listed below, which are widely used in various fields.

The description of relatively low-frequency radiation in a macroscopic environment is carried out using classical electrodynamics. It is based on Maxwell's equations. However, there are simplifications in applications. Optical study uses optics. The 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 significant.

Geometric optical theory is a limiting case in which the wavelength can be ignored. 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 clearly depicting 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 quite arbitrary. Due to the fact that the flow is distributed continuously, the frequency is strictly related to 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 usually called an ultrahigh frequency oscillation (microwave).

Types of electromagnetic waves

Above are the ranges of electromagnetic waves. What types of streams are there? The group includes gamma and x-rays. 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 very conditionally. As a general guideline, the limits of 20 eV - 0.1 MeV are accepted. Gamma fluxes in the narrow sense are emitted by the nucleus, X-ray fluxes 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 fluxes are formed when charged fast particles (protons, electrons and others) 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. As an exception, only the shortest flows, which are adjacent to the infrared region of the spectrum, act. In the radio range, the quantum properties of vibrations appear rather weakly. Nevertheless, they must be taken into account, for example, when analyzing molecular time and frequency standards during cooling of equipment to a temperature of several kelvins.

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

Visible threads

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

The frequencies of optical waves are comparable to those of molecules and atoms, and their lengths are comparable to intermolecular distances and molecular sizes. Therefore, phenomena that are caused by the atomic 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 star's surface (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. This is also where the maximum visual sensitivity is located. Oscillations in the optical range occur when bodies are heated. Infrared flows are therefore also called thermal flows.

The more the body heats up, the higher the frequency where the maximum of the spectrum is located. With a certain increase in temperature, incandescence (glow in the visible range) is observed. In this case, red appears first, then yellow, and so on. The creation and recording of optical flows can occur in biological and chemical reactions, one of which is used in photography. For most creatures living on Earth, photosynthesis serves as a source of energy. This biological reaction occurs 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 the substance also occurs in different ways.

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

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 wavelength 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 from millimeter-scale to the longest (in power lines) are generated.

Structure and strength of flows

Accelerated and periodically changing currents influence each other with certain forces. The direction and their magnitude depend on such factors as the size and configuration of the region 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 impact.

Due to the general complexity of the problem statement, it is impossible to present 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 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. The radiation condition acts as a special additional condition in such cases. Due to it, the “correctness” of the field behavior at infinity is guaranteed.

Chronology of study

Lomonosov in some of his provisions anticipates individual postulates of the theory of the electromagnetic field: the “rotary” (rotational) movement of particles, the “oscillating” (wave) theory of light, its commonality with the nature of electricity, etc. Infrared flows were discovered in 1800 by Herschel (English scientist), and the following year, 1801, Ritter described ultraviolet. Radiation of a shorter range than ultraviolet was discovered by Roentgen in 1895, on November 8. Subsequently it received the name X-ray.

The influence of electromagnetic waves has been studied by many scientists. However, the first to explore the possibilities of flows and the scope of their application was Narkevich-Iodko (Belarusian scientist). 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 the black body. In the process of studying, he discovered the quantum nature of the process. His work marked the beginning of the development. Subsequently, several works by Planck and Einstein were published. Their research led to the formation of such a concept as the photon. This, in turn, marked the beginning of the creation of the quantum theory of electromagnetic fluxes. Its development continued in the works of leading scientific figures of the twentieth century.

Further research and work on the quantum theory of electromagnetic radiation and its interaction with matter ultimately led to the formation of quantum electrodynamics in the form in which it exists today. Among the outstanding scientists who studied this issue, one should name, 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 great. Almost everything that is used in human life today 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 subsequently 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 phenomena being studied with existing standards. It is for this purpose that a complex of measuring instruments and units has been developed within the discipline. A number of patterns are 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 fundamental in many cases. This is due, first of all, to the fact that other disciplines provide descriptions, which, in turn, obey the laws of physics. Thus, 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 radiation exists exactly as long as our Universe lives. It played a key role in the evolution of life on Earth. In fact, this disturbance is the state of an electromagnetic field distributed in space.

Characteristics of electromagnetic radiation

Any electromagnetic wave is described using three characteristics.

1. Frequency.

2. Polarization.

Polarization– one of the main wave attributes. Describes the transverse anisotropy of electromagnetic waves. Radiation is considered polarized when all wave oscillations occur in the same plane.

This phenomenon is actively used in practice. For example, in cinemas when showing 3D films.

Using polarization, IMAX glasses separate the image that is intended for different eyes.

Frequency– the number of wave crests that pass by the observer (in this case, the detector) in one second. It is measured in Hertz.

Wavelength– a specific distance between the nearest points of electromagnetic radiation, the oscillations of which occur in the same phase.

Electromagnetic radiation can propagate in almost any medium: from dense matter to vacuum.

The speed of propagation in a vacuum is 300 thousand km per second.

For an interesting video about the nature and properties of EM waves, watch the video below:

Types of electromagnetic waves

All electromagnetic radiation is divided by frequency.

1. Radio waves. There are short, ultra-short, extra-long, long, medium.

The length of radio waves ranges from 10 km to 1 mm, and from 30 kHz to 300 GHz.

Their sources can be both human activity and various natural atmospheric phenomena.

2. . The wavelength ranges from 1mm to 780nm, and can reach up to 429 THz. Infrared radiation is also called thermal radiation. The basis of all life on our planet.

3. Visible light. Length 400 - 760/780 nm. Accordingly, it fluctuates between 790-385 THz. This includes the entire spectrum of radiation that can be seen by the human eye.

4. . The wavelength is shorter than that of infrared radiation.

Can reach up to 10 nm. such waves are very large - about 3x10^16 Hz.

5. X-rays. waves are 6x10^19 Hz, and the length is about 10 nm - 5 pm.

6. Gamma waves. This includes any radiation that is greater than X-rays, and the length is shorter. The source of such electromagnetic waves is cosmic, nuclear processes.

Scope of application

Somewhere since the end of the 19th century, all human progress has been associated with the practical use of electromagnetic waves.

The first thing worth mentioning is radio communication. It gave people the opportunity to communicate, even if they were far from each other.

Satellite broadcasting and telecommunications are a further development of primitive radio communications.

It is these technologies that have shaped the information image of modern society.

Sources of electromagnetic radiation should be considered both large industrial facilities and various power lines.

Electromagnetic waves are actively used in military affairs (radars, complex electrical devices). Also, medicine could not do without their use. Infrared radiation can be used to treat many diseases.

X-rays help determine damage to a person's internal tissues.

Lasers are used to perform a number of operations that require pinpoint precision.

The importance of electromagnetic radiation in human practical life is difficult to overestimate.

Soviet video about the electromagnetic field:

Possible negative impact on humans

Although useful, strong sources of electromagnetic radiation can cause symptoms such as:

Fatigue;

Headache;

Nausea.

Excessive exposure to certain types of waves causes damage to internal organs, the central nervous system, and the brain. Changes in the human psyche are possible.

An interesting video about the effect of EM waves on humans:

To avoid such consequences, almost all countries in the world have standards governing electromagnetic safety. Each type of radiation has its own regulatory documents (hygienic standards, radiation safety standards). The effect of electromagnetic waves on humans has not been fully studied, so WHO recommends minimizing their exposure.