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, to options implementation of such wireless communication 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 passengers railway send and receive telegrams while the train is 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 electromagnetic wave- this 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 constant value. But with electromagnetic waves, the situation is different. energy and magnetic and electric field reach maximum values at the same time.
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.
Technological progress also has a downside. The global use of various electrically powered technologies has caused pollution, which has been given the name - electromagnetic noise. In this article, we will consider the nature of this phenomenon, the degree of its impact on the human body and protective measures.
What is it and sources of radiation
Electromagnetic radiation is electromagnetic waves that occur when a magnetic or electric field is disturbed. Modern physics interprets this process within the framework of the theory of corpuscular-wave dualism. That is, the minimum portion of electromagnetic radiation is a quantum, but at the same time it has frequency-wave properties that determine its main characteristics.
The frequency spectrum of the electromagnetic field radiation makes it possible to classify it into the following types:
- radio frequency (these include radio waves);
- thermal (infrared);
- optical (that is, visible to the eye);
- radiation in the ultraviolet spectrum and hard (ionized).
A detailed illustration of the spectral range (electromagnetic emission scale) can be seen in the figure below.
Nature of radiation sources
Depending on the origin, sources of radiation of electromagnetic waves in world practice are usually classified into two types, namely:
- perturbations of the electromagnetic field of artificial origin;
- radiation from natural sources.
Radiations coming from the magnetic field around the Earth, electrical processes in the atmosphere of our planet, nuclear fusion in the depths of the sun - all of them are of natural origin.
As for artificial sources, they are a side effect caused by the operation of various electrical mechanisms and devices.
The radiation emanating from them can be low-level and high-level. The degree of intensity of the electromagnetic field radiation completely depends on the power levels of the sources.
Examples of high EMP sources include:
- Power lines are usually high-voltage;
- all types of electric transport, as well as the accompanying infrastructure;
- television and radio towers, as well as mobile and mobile communication stations;
- installations for converting the voltage of the electrical network (in particular, waves emanating from a transformer or distribution substation);
- elevators and other types of lifting equipment where an electromechanical power plant is used.
Typical sources emitting low-level radiation include the following electrical equipment:
- almost all devices with a CRT display (for example: a payment terminal or a computer);
- various types of household appliances, ranging from irons to climate systems;
- engineering systems that provide electricity to various objects (it means not only a power cable, but related equipment, such as sockets and electricity meters).
Separately, it is worth highlighting the special equipment used in medicine, which emits hard radiation (X-ray machines, MRI, etc.).
Impact on a person
In the course of numerous studies, radiobiologists came to a disappointing conclusion - prolonged radiation of electromagnetic waves can cause an "explosion" of diseases, that is, it causes the rapid development of pathological processes in the human body. Moreover, many of them introduce violations at the genetic level.
Video: How electromagnetic radiation affects people.
https://www.youtube.com/watch?v=FYWgXyHW93Q
This is due to the fact that the electromagnetic field high level biological activity, which negatively affects living organisms. The influence factor depends on the following components:
- the nature of the radiation produced;
- how long and with what intensity it continues.
The impact on human health of radiation, which has an electromagnetic nature, directly depends on the localization. It can be either local or general. In the latter case, large-scale irradiation occurs, for example, radiation produced by power lines.
Accordingly, local irradiation refers to the impact on certain parts of the body. Electromagnetic waves emanating from an electronic watch or a mobile phone are a vivid example of a local effect.
Separately, it is necessary to note the thermal effect of high-frequency electromagnetic radiation on living matter. The field energy is converted into thermal energy(due to the vibration of molecules), this effect is based on the work of industrial microwave emitters used for heating various substances. Unlike benefits in industrial processes, thermal effects on the human body can be detrimental. From the point of view of radiobiology, it is not recommended to be near "warm" electrical equipment.
It must be taken into account that in everyday life we are regularly exposed to radiation, and this happens not only at work, but also at home or when moving around the city. Over time, the biological effect accumulates and intensifies. With the growth of electromagnetic noise, the number of characteristic diseases of the brain or nervous system. Note that radiobiology is a fairly young science, so the harm caused to living organisms from electromagnetic radiation has not been thoroughly studied.
The figure shows the level of electromagnetic waves produced by conventional household appliances.
Note that the field strength level decreases significantly with distance. That is, in order to reduce its effect, it is enough to move away from the source at a certain distance.
The formula for calculating the norm (rationing) of electromagnetic field radiation is indicated in the relevant GOSTs and SanPiNs.
Radiation protection
In production, absorbing (protective) screens are actively used as a means of protecting against radiation. Unfortunately, it is not possible to protect yourself from electromagnetic field radiation using such equipment at home, since it is not designed for this.
- to reduce the impact of electromagnetic field radiation to almost zero, you should move away from power lines, radio and television towers at a distance of at least 25 meters (you must take into account the power of the source);
- for a CRT monitor and a TV, this distance is much smaller - about 30 cm;
- electronic watches should not be placed close to the pillow, the optimal distance for them is more than 5 cm;
- as for radios and cell phones, bringing them closer than 2.5 centimeters is not recommended.
Note that many people know how dangerous it is to stand near high-voltage power lines, but at the same time, most people do not attach importance to ordinary household electrical appliances. Although it is enough to put the system unit on the floor or move it away, and you will protect yourself and your loved ones. We advise you to do this, and then measure the background from the computer using an electromagnetic field radiation detector in order to visually verify its reduction.
This advice also applies to the placement of the refrigerator, many put it near the kitchen table, practical but unsafe.
No table will be able to indicate the exact safe distance from a particular electrical equipment, since emissions may vary, both depending on the model of the device and the country of manufacture. At the moment, there is no single international standard, therefore, in different countries standards may differ significantly.
You can accurately determine the intensity of radiation using a special device - a fluxmeter. According to the standards adopted in Russia, the maximum allowable dose should not exceed 0.2 μT. We recommend measuring in the apartment using the above-mentioned device for measuring the degree of electromagnetic field radiation.
Fluxmeter - a device for measuring the degree of radiation of an electromagnetic field Try to reduce the time when you are exposed to radiation, that is, do not stay close to working electrical appliances for a long time. For example, it is not at all necessary to constantly stand at the electric stove or microwave oven while cooking. Regarding electrical equipment, you can see that warm does not always mean safe.
Always turn off electrical appliances when not in use. People often leave various devices turned on, not considering that at this time electromagnetic radiation is emitted from electrical equipment. Turn off your laptop, printer or other equipment, it is unnecessary to be exposed to radiation once again, remember about your safety.
In 1860-1865. one of the greatest physicists of the 19th century James Clerk Maxwell created a theory electromagnetic field. According to Maxwell, the phenomenon of electromagnetic induction is explained as follows. If at some point in space the magnetic field changes with time, then an electric field is also formed there. If there is a closed conductor in the field, then the electric field causes an induction current in it. It follows from Maxwell's theory that the reverse process is also possible. If in some region of space the electric field changes with time, then a magnetic field is also formed here.
Thus, any change in the magnetic field over time results in a changing electric field, and any change over time in the electric field gives rise to a changing magnetic field. These mutually generating variables are electrical and magnetic fields form a single electromagnetic field.
Properties of electromagnetic waves
The most important result that follows from the theory of the electromagnetic field formulated by Maxwell was the prediction of the possibility of the existence of electromagnetic waves. electromagnetic wave- propagation of electromagnetic fields in space and time.
Electromagnetic waves, unlike elastic (sound) waves, can propagate in a vacuum or any other substance.
Electromagnetic waves in vacuum propagate at a speed c=299 792 km/s, that is, at the speed of light.
In matter, the speed of an electromagnetic wave is less than in vacuum. The relationship between the wavelength, its speed, period and frequency of oscillations obtained for mechanical waves is also valid for electromagnetic waves:
Tension vector fluctuations E and magnetic induction vector B take place in mutual perpendicular planes and perpendicular to the direction of wave propagation (velocity vector).
An electromagnetic wave carries energy.
Electromagnetic Wave Range
Around us complex world electromagnetic waves of various frequencies: radiation from computer monitors, cell phones, microwave ovens, televisions, etc. Currently, all electromagnetic waves are divided by wavelength into six main ranges.
radio waves- these are electromagnetic waves (with a wavelength from 10,000 m to 0.005 m), which serve to transmit signals (information) over a distance without wires. In radio communications, radio waves are created by high frequency currents flowing in an antenna.
Electromagnetic radiation with a wavelength from 0.005 m to 1 micron, i.e. between radio waves and visible light are called infrared radiation. Infrared radiation is emitted by any heated body. The source of infrared radiation are furnaces, batteries, electric incandescent lamps. With the help of special devices, infrared radiation can be converted into visible light and receive images of heated objects in complete darkness.
To visible light refer to radiation with a wavelength of approximately 770 nm to 380 nm, from red to purple. The significance of this part of the spectrum of electromagnetic radiation in human life is extremely high, since a person receives almost all information about the world around him with the help of vision.
Electromagnetic radiation invisible to the eye with a wavelength shorter than violet is called ultraviolet radiation. It can kill pathogenic bacteria.
x-ray radiation invisible to the eye. It passes without significant absorption through significant layers of a substance that is opaque to visible light, which is used to diagnose diseases. internal organs.
Gamma radiation called electromagnetic radiation emitted by excited nuclei and arising from the interaction of elementary particles.
The principle of radio communication
The oscillatory circuit is used as a source of electromagnetic waves. For effective radiation, the circuit is "opened", i.e. create conditions for the field to "go" into space. This device is called open oscillatory circuit - antenna.
radio communication called the transmission of information using electromagnetic waves, the frequencies of which are in the range from to Hz.
Radar (radar)
A device that transmits ultrashort waves and immediately receives them. The radiation is carried out by short pulses. Pulses are reflected from objects, allowing, after receiving and processing the signal, to set the distance to the object.
The speed radar works on a similar principle. Think about how radar determines the speed of a moving car.
Electromagnetic radiation exists exactly as long as our Universe lives. It has played a key role in the evolution of life on Earth. In fact, this is a perturbation of the state of the electromagnetic field propagating 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 the cinema when showing 3D films.
With the help of polarization, IMAX glasses separate the image, which is intended for different eyes. 
Frequency is the number of wave crests that pass by the observer (in this case, the detector) in one second. Measured in hertz.
Wavelength- a specific distance between the nearest points of electromagnetic radiation, oscillations of which occur in one phase.
Electromagnetic radiation can propagate in almost any medium: from dense matter to vacuum.
The speed of propagation in vacuum is 300 thousand km per second.
Interesting video about the nature and properties of EM waves, see 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 activities and various natural atmospheric phenomena.
2. . The wavelength lies within 1mm - 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 - 760/780nm. 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 in infrared radiation.
It can reach up to 10 nm. such waves is very large - about 3x10 ^ 16 Hz.
5. X-rays. waves 6x10 ^ 19 Hz, and the length is about 10 nm - 5 pm.
6. Gamma waves. This includes any radiation, which is greater than in x-rays, and the length is less. The source of such electromagnetic waves are cosmic, nuclear processes.
Scope of application
Somewhere from late XIX century, all human progress has been linked to practical application electromagnetic waves.
The first thing worth mentioning is radio communication. She made it possible for people to communicate, even if they were far from each other.
Satellite broadcasting, telecommunications are further development primitive radio.
It is these technologies that have shaped the information image modern society.
Sources of electromagnetic radiation should be considered as large industrial facilities, as well as various power lines.
Electromagnetic waves are actively used in military affairs (radar, complex electrical devices). Also, medicine has not done without their use. Infrared radiation can be used to treat many diseases.
X-rays help identify damage to a person's internal tissues.
With the help of lasers, a number of operations are carried out that require jewelry precision. 
Importance of electromagnetic radiation in practical life It's hard to overestimate a person.
Soviet video about the electromagnetic field:
Possible negative impact on humans
Despite their usefulness, strong sources of electromagnetic radiation can cause the following symptoms:
Fatigue;
Nausea.
Excessive exposure to certain types of waves cause 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 a person:
To avoid such consequences, almost all countries of 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 is not fully understood, therefore WHO recommends minimizing their impact.
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 perturbation propagating in space, that is, if some kind of perturbation has occurred somewhere, and it spreads in all directions, then we can say that the propagation of this perturbation is nothing more than a wave phenomenon.
Electromagnetic waves are electromagnetic oscillations, which 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 called an electromagnetic field propagating in space or an electromagnetic disturbance.
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 it has been proven that they exist together. But it turns out that they can exist completely in the absence of any substance. This is a very important conclusion and was made in the works of James Clerk Maxwell.
It turns out that an electromagnetic field can exist even where there is no substance. Here we were talking about 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 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 produce the emission of an electromagnetic wave, and the reception of an electromagnetic wave, was the German scientist Heinrich Hertz. He was the first to create such an installation for the emission and reception of an electromagnetic wave.
The first thing we must say here is that in order to emit an electromagnetic wave, we need, of course, a fairly fast moving electric charge. We must create such a device where there will be a very rapidly moving or accelerated electric charge.
Heinrich Hertz, with the help of his experiments, proved that in order to obtain a powerful and sufficiently perceptible electromagnetic wave, a moving electric charge must oscillate at a very high frequency, that is, of 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 propagate in all directions. That is, it 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 it was about these properties that it was 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 wavelengths, electromagnetic waves are divided into ranges. They have a rather conditional scale, since neighboring ranges have the properties of overlapping each other.
It will not be superfluous to know that some areas have common properties. These properties include:
Penetration ability;
high speed of propagation in the substance;
impact 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 take a closer look at the table below, and study in more detail how electromagnetic waves can be classified, what types of radiation, radiation sources, and their frequency are:
Interesting facts about electromagnetic waves
Probably, it will not be a secret for 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 can have various titles but their essence is the same. Such electromagnetic waves include both radio waves and infrared radiation, and visible light, and X-rays, as well as the rays of the biofield.
Such a limitless source of energy as an electromagnetic field is the cause of the oscillation electric charges atoms and molecules. From this it follows that, oscillating, the charge moves with acceleration and at the same time radiates 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 paid attention to the fact 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 germicidal lamps, which are used to disinfect rooms, you must be extremely careful and when using them, you must leave the room, as they adversely affect human skin, as well as plants, causing leaf burns.
But in addition to the radiation sources and various devices that surround 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 change constantly.
To determine the electromagnetic field of a person, such an accurate device as an encephalograph is used. Using this device, it is possible to measure the electromagnetic field of a person with high accuracy and determine its activity in the cerebral cortex. Thanks to the emergence of such a device as an encephalograph, it became possible to diagnose various diseases even at an early stage.
