Shmelev V.E., Sbitnev S.A. theoretical foundations of electrical engineering

1. Introduction. The subject of study in valeology.

3. The main sources of the electromagnetic field.

5. Methods for protecting people's health from electromagnetic exposure.

6. List of used materials and literature.

1. Introduction. The subject of study in valeology.

1.1 Introduction.

Valeology - from lat. "valeo" - "hello" - scientific discipline that studies the individual health of a healthy person. The fundamental difference between valeology and other disciplines (in particular, from practical medicine) lies precisely in the individual approach to assessing the health of each specific subject (without taking into account general and average data for any group).

For the first time, valeology as a scientific discipline was officially registered in 1980. Its founder was the Russian scientist I. I. Brekhman, who worked at Vladivostok State University.

Currently, the new discipline is actively developing, scientific works are accumulating, and practical research is being actively conducted. Gradually, there is a transition from the status of a scientific discipline to the status of an independent science.

1.2 The subject of study in valeology.

The subject of study in valeology is the individual health of a healthy person and the factors affecting it. Also, valeology is engaged in the systematization of a healthy lifestyle, taking into account the individuality of a particular subject.

The most common definition of the concept of "health" at the moment is the definition proposed by the experts of the World Health Organization (WHO):

Health is a state of physical, mental and social well-being.

Modern valeology identifies the following main characteristics of individual health:

1. Life is the most complex manifestation of the existence of matter, which surpasses in complexity various physicochemical and bioreactions.

2. Homeostasis - a quasi-static state of life forms, characterized by variability over relatively large time periods and practical staticity - at short ones.

3. Adaptation - the property of life forms to adapt to changing conditions of existence and overload. With violations of adaptation or too sharp and radical changes in conditions, maladaptation occurs - stress.

4. Phenotype - a combination of environmental factors that affect the development of a living organism. Also, the term "phenotype" characterizes the totality of the developmental features and physiology of the organism.

5. Genotype - a combination of hereditary factors affecting the development of a living organism, which is a combination of the genetic material of the parents. When deformed genes are transmitted from parents, hereditary pathologies arise.

6. Lifestyle - a set of behavioral stereotypes and norms that characterize a particular organism.

Health (as defined by WHO).

2. Electromagnetic field, its types, characteristics and classification.

2.1 Basic definitions. Types of electro magnetic field.

An electromagnetic field is a special form of matter through which interaction between electrically charged particles is carried out.

Electric field - created by electric charges and charged particles in space. The figure shows a picture of field lines (imaginary lines used to visualize fields) of an electric field for two charged particles at rest:

Magnetic field - created when electric charges move through a conductor. The pattern of field lines for a single conductor is shown in the figure:

Physical reason for existence electromagnetic field is that a time-varying electric field excites a magnetic field, and a changing magnetic field excites a vortex electric field. Continuously changing, both components support the existence of the electromagnetic field. The field of a stationary or uniformly moving particle is inextricably linked with a carrier (charged particle).

However, with the accelerated movement of carriers, the electromagnetic field “breaks away” from them and exists in the environment independently, in the form of an electromagnetic wave, without disappearing with the removal of the carrier (for example, radio waves do not disappear when the current disappears (movement of carriers - electrons) in the antenna emitting them).

2.2 Basic characteristics of the electromagnetic field.

The electric field is characterized by the strength of the electric field (designation "E", SI unit - V/m, vector). The magnetic field is characterized by the strength of the magnetic field (designation "H", SI dimension - A/m, vector). The module (length) of the vector is usually measured.

Electromagnetic waves are characterized by a wavelength (designation "(", SI dimension - m), a source emitting them - frequency (designation - "(", SI dimension - Hz). In the figure, E is the electric field strength vector, H is the magnetic field strength vector .

At frequencies of 3 - 300 Hz, the concept of magnetic induction can also be used as a characteristic of the magnetic field (designation "B", SI unit - T).

2.3 Classification of electromagnetic fields.

The most used is the so-called "zonal" classification of electromagnetic fields according to the degree of remoteness from the source/carrier.

According to this classification, the electromagnetic field is divided into "near" and "far" zones. The “near” zone (sometimes called the induction zone) extends up to a distance from the source equal to 0-3 (, de (- the length of the electromagnetic wave generated by the field. In this case, the field strength decreases rapidly (proportionally to the square or cube of the distance to the source). In this zone generated electromagnetic wave is not yet fully formed.

The “far” zone is the zone of the formed electromagnetic wave. Here, the field strength decreases inversely with the distance to the source. In this zone, the experimentally determined relation between the strengths of the electric and magnetic fields is valid:

where 377 is a constant, vacuum impedance, Ohm.

Electromagnetic waves are usually classified according to frequencies:

| Extreme low, | | Hz | Decamegameter | Mm |

| Ultra-low, VLF | | Hz | Megameter | Mm |

| Very low, VLF | KHz | Myriameter | km |

| Low frequencies, bass | | KHz|Kilometer | km |

| Average, MF | | MHz | Hectometric | km |

| High, HF | | MHz | Decameter | m |

|Very high, VHF| MHz|Meter | m |

|Ultra-high, UHF| GHz | Decimeter | m |

| Ultra high, microwave | | GHz | Centimeter | cm |

| Extremely high, | | GHz|Millimeter | mm |

Usually only the electric field strength E is measured. At frequencies above 300 MHz, the energy flux density of the wave, or the Poynting vector, is sometimes measured (designation “S”, SI unit is W/m2).

3. The main sources of the electromagnetic field.

The main sources of the electromagnetic field are:

Power lines.

Wiring (inside buildings and structures).

Household electrical appliances.

Personal computers.

TV and radio transmitting stations.

Satellite and cellular communications (devices, repeaters).

Electric transport.

radar installations.

3.1 Power lines (TL).

The wires of a working power line create an electromagnetic field of industrial frequency (50 Hz) in the adjacent space (at distances of the order of tens of meters from the wire). Moreover, the field strength near the line can vary over a wide range, depending on its electrical load. The standards set the boundaries of sanitary protection zones near power lines (according to SN 2971-84):

| Operating voltage | 330 and below | 500 | 750 | 1150 |

| Size | 20 | 30 | 40 | 55 |

(in fact, the boundaries of the sanitary protection zone are established along the boundary line of the maximum electric field strength, which is the most distant from the wires, equal to 1 kV / m).

3.2 Wiring.

Electrical wiring includes: power cables for building life support systems, power distribution wires, as well as branching boards, power boxes and transformers. Electrical wiring is the main source of the industrial frequency electromagnetic field in residential premises. In this case, the level of the electric field strength emitted by the source is often relatively low (does not exceed 500 V/m).

3.3 Household electrical appliances.

Sources of electromagnetic fields are all household appliances that operate using electric current. At the same time, the level of radiation varies over the widest range, depending on the model, the device device and the specific mode of operation. Also, the level of radiation strongly depends on the power consumption of the device - the higher the power, the higher the level of the electromagnetic field during the operation of the device. The electric field strength near household appliances does not exceed tens of V/m.

The table below shows the maximum allowable levels of magnetic induction for the most powerful magnetic field sources among household electrical appliances:

| Device | Limit interval | |

| | values of magnetic induction, μT |

|Coffee maker | |

| Washing machine | |

| Iron | |

| Vacuum cleaner | |

| Electric stove | |

| Lamp "fluorescent light" (fluorescent lamps LTB, | | |

| Electric drill (motor | |

| Power W) | | |

| Electric mixer (power motor | |

| W) | |

| TV | |

| Microwave oven (induction, microwave) | | |

3.4 Personal computers.

The primary source of adverse health effects for a computer user is the monitor's display device (VOD). In most modern monitors, the CBO is a cathode ray tube. The table lists the main health impacts of SVR:

| Ergonomic | Factors of influence of electromagnetic | |

| | field cathode ray tube | |

| Significant reduction in contrast | Electromagnetic field in the frequency | |

| reproduced image in the conditions | MHz range. |

| external illumination of the screen with direct beams | | |

| light. | | |

| Mirror reflection of light rays from | Electrostatic charge on the surface | |

| Cartoon character | Ultraviolet radiation (range |

| image reproduction | wavelengths nm). |

| (high-frequency continuous update | |

| Discrete nature of the image | Infrared and X-ray |

| (subdivision into points). | ionizing radiation. |

In the future, we will consider only the factors of the influence of the electromagnetic field of the cathode-ray tube as the main factors of the influence of the SVR on health.

In addition to the monitor and the system unit, a personal computer may also include a large number of other devices (such as printers, scanners, network filters, etc.). All these devices work with the use of electric current, which means that they are sources of an electromagnetic field. The following table shows the electromagnetic environment near the computer (the contribution of the monitor is not taken into account in this table, as it was discussed earlier):

| Source | Frequency range generated | |

| | electromagnetic field | |

| System unit assembly. | |. |

| Input-output devices (printers, | Hz. |

| scanners, drives, etc.). | |

| Uninterruptible power supplies, |. |

| network filters and stabilizers. | | |

The electromagnetic field of personal computers has the most complex wave and spectral composition and is difficult to measure and quantify. It has magnetic, electrostatic and radiation components (in particular, the electrostatic potential of a person sitting in front of a monitor can range from -3 to +5 V). Given the fact that personal computers are now actively used in all branches of human activity, their impact on human health is subject to careful study and control.

3.5 Television and radio transmitting stations.

A significant number of radio broadcasting stations and centers of various affiliations are currently located on the territory of Russia.

Transmitting stations and centers are located in zones specially designated for them and can occupy rather large territories (up to 1000 ha). By their structure, they include one or more technical buildings, where radio transmitters are located, and antenna fields, on which up to several dozen antenna-feeder systems (AFS) are located. Each system includes a radiating antenna and a feeder line that brings the broadcast signal.

The electromagnetic field emitted by the antennas of radio broadcasting centers has a complex spectral composition and an individual distribution of strengths depending on the configuration of the antennas, the terrain and the architecture of the adjacent buildings. Some averaged data for various types of radio broadcasting centers are presented in the table:

| | field, V / m. | A / m. | |

| DV - radio | 630 | 1.2 | Highest tension |

| kHz, | | | distances less than 1 length | |

|500 kW). | | | |

|200 kW). | | | |

| HF - radio | 44 | 0.12 | Transmitters can be | |

|MHz, | | | Densely built | |

|100 kW). | | | |

| MHz, | | | building level. | |

3.6 Satellite and cellular communication.

3.6.1 Satellite communications.

Satellite communication systems consist of a transmitting station on Earth and travelers - repeaters in orbit. Transmitting satellite communication stations emit a narrowly directed wave beam, the energy flux density in which reaches hundreds of W/m. Satellite communication systems create high electromagnetic field strengths at considerable distances from antennas. For example, a station with a power of 225 kW, operating at a frequency of 2.38 GHz, creates an energy flux density of 2.8 W/m2 at a distance of 100 km. The scattering of energy relative to the main beam is very small and occurs most of all in the area of \u200b\u200bthe direct placement of the antenna.

3.6.2 Cellular communication.

Cellular radiotelephony is today one of the most intensively developing telecommunication systems. The main elements of a cellular communication system are base stations and mobile radiotelephones. Base stations maintain radio communication with mobile devices, as a result of which they are sources of an electromagnetic field. The system uses the principle of dividing the coverage area into zones, or so-called "cells", with a radius of km. The following table presents the main characteristics of cellular communication systems operating in Russia:

| | | | | Tue. | km. |

|NMT450. | |

| Analog. |5] |5] | | | |

|AMPS. |||100 |0.6 | |

|DAMPS (IS – |||50 |0.2 | |

|136). | | | | | |

|CDMA. |||100 |0.6 | |

|GSM - 900. |||40 |0.25 | |

|GSM - 1800. | |

|Digital. |0] |5] | | | |

The radiation intensity of the base station is determined by the load, that is, the presence of cell phone owners in the service area of a particular base station and their desire to use the phone for a conversation, which, in turn, fundamentally depends on the time of day, location of the station, day of the week and other factors. At night, the loading of stations is almost zero. The radiation intensity of mobile devices depends largely on the state of the communication channel "mobile radiotelephone - base station" (the greater the distance from the base station, the higher the radiation intensity of the device).

3.7 Electric transport.

Electric transport (trolleybuses, trams, metro trains, etc.) is a powerful source of electromagnetic field in the Hz frequency range. At the same time, in the vast majority of cases, the traction electric motor acts as the main emitter (for trolleybuses and trams, air current collectors compete with the electric motor in terms of the strength of the radiated electric field). The table shows data on the measured value of magnetic induction for some types of electric transport:

| Mode of transport and genus | Average value | Maximum value |

| Suburban trains. | 20 | 75 |

| Electric transport with | 29 | 110 |

| DC drive | | |

| (electric cars, etc.). | | |

3.8 Radar installations.

Radar and radar installations usually have reflector-type antennas (“dishes”) and emit a narrowly directed radio beam.

Periodic movement of the antenna in space leads to spatial discontinuity of radiation. There is also a temporary discontinuity of radiation due to the cyclic operation of the radar for radiation. They operate at frequencies from 500 MHz to 15 GHz, but some special installations can operate at frequencies up to 100 GHz or more. Due to the special nature of the radiation, they can create zones with a high energy flux density (100 W/m2 or more) on the ground.

4. The influence of the electromagnetic field on individual human health.

The human body always reacts to an external electromagnetic field. Due to the different wave composition and other factors, the electromagnetic field of various sources affects human health in different ways. Therefore, in this section, the impact of various sources on health will be considered separately. However, the field of artificial sources, which is sharply dissonant with the natural electromagnetic background, in almost all cases has a negative impact on the health of people in the zone of its influence.

Extensive studies of the influence of electromagnetic fields on health were started in our country in the 60s. It was found that the human nervous system is sensitive to electromagnetic effects, and that the field has a so-called information effect when exposed to a person at intensities below the threshold value of the thermal effect (the field strength value at which its thermal effect begins to manifest itself).

The following table lists the most common complaints about the deterioration in the health of people who are in the zone of influence of the field of various sources. The sequence and numbering of sources in the table correspond to their sequence and numbering adopted in section 3:

| Source | The most common complaints. |

| electromagnetic | |

|1. Lines | Short-term exposure (of the order of several minutes) is capable of |

| Power lines (power lines). | | lead to a negative reaction only in particularly sensitive | |

| | people or patients with certain types of allergic | |

| | various pathologies of the cardiovascular and nervous systems |

| | (due to the imbalance of the subsystem of the nervous regulation). When |

| | ultra-long (about 10-20 years) continuous exposure | |

| | perhaps (according to unverified data) the development of some | |

| | oncological diseases. | |

|2. Internal | To date, data on complaints of deterioration | |

| electrical wiring of buildings | health, directly related to the work of internal | |

|3. Household | There are unverified data on complaints of skin, |

| | systematic use of microwave ovens old | |

| | data on the use of microwave ovens all | |

| | Models in a production environment (for example, to warm up | |

| | food in a cafe). In addition to microwave ovens, there is information about |

| | negative impact on people's health TVs in | |

| | as an imaging device cathode ray tube. | |

Electromagnetic field, a special form of matter. By means of an electromagnetic field, interaction between charged particles is carried out.

The behavior of an electromagnetic field is studied by classical electrodynamics. The electromagnetic field is described by Maxwell's Equations, which connect the quantities that characterize the field with its sources, that is, with charges and currents distributed in space. The electromagnetic field of stationary or uniformly moving charged particles is inextricably linked with these particles; as particles move faster, the electromagnetic field "breaks away" from them and exists independently in the form of electromagnetic waves.

It follows from Maxwell's equations that an alternating electric field generates a magnetic field, and an alternating magnetic field generates an electric one, so an electromagnetic field can exist in the absence of charges. The generation of an electromagnetic field by an alternating magnetic field and a magnetic field by an alternating electric one leads to the fact that electric and magnetic fields do not exist separately, independently of each other. Therefore, the electromagnetic field is a type of matter, determined at all points by two vector quantities that characterize its two components - "electric field" and "magnetic field", and exerting a force on charged particles, depending on their speed and the magnitude of their charge.

An electromagnetic field in a vacuum, that is, in a free state, not associated with particles of matter, exists in the form of electromagnetic waves, and propagates in a vacuum in the absence of very strong gravitational fields at a speed equal speed Sveta c= 2.998. 10 8 m/s. Such a field is characterized by the strength of the electric field E and magnetic field induction V... To describe the electromagnetic field in the medium, the quantities of electric induction are also used D and magnetic field strength H... In matter, as well as in the presence of very strong gravitational fields, that is, near very large masses of matter, the propagation velocity of the electromagnetic field is less than the value c.

The components of the vectors characterizing the electromagnetic field form, according to the theory of relativity, a single physical quantity- electromagnetic field tensor, the components of which are transformed during the transition from one inertial frame of reference to another in accordance with the Lorentz transformations.

An electromagnetic field has energy and momentum. The existence of an electromagnetic field pulse was first discovered experimentally in the experiments of P. N. Lebedev on measuring the pressure of light in 1899. An electromagnetic field always has energy. Energy density of the electromagnetic field = 1/2(ED+HH).

The electromagnetic field propagates in space. The energy flux density of the electromagnetic field is determined by the Poynting vector S=, unit W/m 2 . The direction of the Poynting vector is perpendicular E and H and coincides with the direction of propagation of electromagnetic energy. Its value is equal to the energy transferred through a unit area perpendicular to S per unit of time. Field momentum density in vacuum K \u003d S / s 2 \u003d / s 2.

At high frequencies of the electromagnetic field, its quantum properties become significant and the electromagnetic field can be considered as a flux of field quanta - photons. In this case, the electromagnetic field is described

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 generating each other alternating electric 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 occur in mutually perpendicular planes and perpendicular to the direction of wave propagation (velocity vector).

An electromagnetic wave carries energy.

Electromagnetic Wave Range

Around us is a complex world of 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 images of heated objects can be obtained in complete darkness.

TO visible light include radiation with a wavelength of approximately 770 nm to 380 nm, from red to violet. The significance of this part of the spectrum of electromagnetic radiation in human life is exceptionally great, 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 of 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 an 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)

The device that transmits ultrashort waves and immediately accepts 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.

An electromagnetic field is an alternating electric and magnetic field that generates each other.
The electromagnetic field theory was created by James Maxwell in 1865.

He theoretically proved that:
any change in the magnetic field over time results in a changing electric field, and any change in the electric field over time gives rise to a changing magnetic field.
If electric charges move with acceleration, then the electric field created by them periodically changes and itself creates an alternating magnetic field in space, etc.

The sources of the electromagnetic field can be:
- moving magnet;
- an electric charge moving with acceleration or oscillating (unlike a charge moving at a constant speed, for example, in the case of a direct current in a conductor, a constant magnetic field is created here).

An electric field always exists around an electric charge, in any frame of reference, a magnetic field exists in the one relative to which electric charges move.
The electromagnetic field exists in the frame of reference, relative to which electric charges move with acceleration.

TRY SOLUTION

A piece of amber was rubbed against a cloth and charged with static electricity. What field can be found around immobile amber? Around moving?

A charged body is at rest relative to the earth's surface. The car moves uniformly and rectilinearly relative to the surface of the earth. Is it possible to detect a constant magnetic field in the reference frame associated with the car?

What field arises around an electron if it: is at rest; moving at a constant speed; moving with acceleration?

A kinescope creates a stream of uniformly moving electrons. Is it possible to detect a magnetic field in a frame of reference associated with one of the moving electrons?

ELECTROMAGNETIC WAVES

Electromagnetic waves are an electromagnetic field propagating in space at a finite speed, depending on the properties of the medium

Properties of electromagnetic waves:
- propagate not only in matter, but also in vacuum;
- propagate in vacuum at the speed of light (С = 300,000 km/s);
are transverse waves
- these are traveling waves (transfer energy).

The source of electromagnetic waves are rapidly moving electric charges.
Oscillations of electric charges are accompanied by electromagnetic radiation having a frequency equal to the frequency of charge oscillations.

SCALE OF ELECTROMAGNETIC WAVES

All the space around us is permeated with electromagnetic radiation. The sun, the bodies around us, transmitter antennas emit electromagnetic waves, which, depending on their frequency of oscillation, have different names.

Radio waves are electromagnetic waves (with a wavelength from more than 10,000m to 0.005m) that are used to transmit signals (information) over a distance without wires.
In radio communications, radio waves are created by high frequency currents flowing in an antenna.
Radio waves of different lengths propagate differently.

Electromagnetic radiation with a wavelength less than 0.005 m but greater than 770 nm, i.e., lying between the radio wave range and the visible light range, is called infrared radiation (IR).
Infrared radiation is emitted by any heated body. Sources of infrared radiation are stoves, water heaters, electric incandescent lamps. With the help of special devices, infrared radiation can be converted into visible light and images of heated objects can be obtained in complete darkness. Infrared radiation is used for drying painted products, building walls, wood.

Visible light includes radiation with a wavelength of approximately 770nm to 380nm, from red to violet light. The values of this section of the spectrum of electromagnetic radiation in human life are exceptionally large, since almost all information about the world around a person receives through vision. Light is a prerequisite for the development of green plants and, therefore, a necessary condition for the existence of life on Earth.

Invisible to the eye, electromagnetic radiation with a wavelength shorter than that of violet light is called ultraviolet radiation (UV). Ultraviolet radiation can kill pathogenic bacteria, so it is widely used in medicine. UV radiation included sunlight causes biological processes that lead to darkening of human skin - sunburn. Discharge lamps are used as sources of ultraviolet radiation in medicine. The tubes of such lamps are made of quartz, which is transparent to ultraviolet rays; therefore these lamps are called quartz lamps.

X-rays (Ri) are invisible to the atom. They pass without significant absorption through significant layers of material that is opaque to visible light. X-rays are detected by their ability to cause a certain glow of certain crystals and act on photographic film. The ability of X-rays to penetrate through thick layers of substances is used to diagnose diseases of human internal organs.

An electromagnetic field is a kind of matter that arises around moving charges. For example, around a conductor with current. The electromagnetic field consists of two components - electric and magnetic fields. They cannot exist independently of each other. One begets the other. When the electric field changes, a magnetic field immediately arises. Electromagnetic wave propagation speed V=C/EM where e and m respectively, the magnetic and dielectric permittivities of the medium in which the wave propagates. An electromagnetic wave in a vacuum travels at the speed of light, that is, 300,000 km/s. Since the dielectric and magnetic permeability of the vacuum is considered equal to 1. When the electric field changes, a magnetic field arises. Since the electric field that caused it is not constant (that is, it changes over time), the magnetic field will also be variable. The changing magnetic field in turn generates an electric field, and so on. Thus, for the subsequent field (whether it is electric or magnetic), the source will be the previous field, and not the original source, that is, a current-carrying conductor. Thus, even after the current is turned off in the conductor, the electromagnetic field will continue to exist and spread in space. An electromagnetic wave propagates in space in all directions from its source. You can imagine turning on a light bulb, the rays of light from it spread in all directions. An electromagnetic wave during propagation carries energy in space. The stronger the current in the conductor that caused the field, the greater the energy carried by the wave. Also, the energy depends on the frequency of the emitted waves, with an increase in it by 2.3.4 times, the energy of the wave will increase by 4.9.16 times, respectively. That is, the propagation energy of the wave is proportional to the square of the frequency. The best conditions for wave propagation are created when the length of the conductor is equal to the wavelength. The lines of force of magnetic and electric will fly mutually perpendicular. Magnetic lines of force envelop a current-carrying conductor and are always closed. Electric lines of force go from one charge to another. An electromagnetic wave is always a transverse wave. That is, the lines of force, both magnetic and electric, lie in a plane perpendicular to the direction of propagation. The intensity of the electromagnetic field is the power characteristic of the field. Also tension is a vector quantity, that is, it has a beginning and a direction. The field strength is directed tangentially to the lines of force. Since the strength of the electric and magnetic fields are perpendicular to each other, there is a rule by which the direction of wave propagation can be determined. When the screw rotates along the shortest path from the electric field strength vector to the magnetic field strength vector, the translational movement of the screw will indicate the direction of wave propagation.

Magnetic field and its characteristics. When an electric current passes through a conductor, a a magnetic field. A magnetic field is one of the types of matter. It has energy, which manifests itself in the form of electromagnetic forces acting on individual moving electric charges (electrons and ions) and on their flows, i.e. electric current. Under the influence of electromagnetic forces, moving charged particles deviate from their original path in a direction perpendicular to the field (Fig. 34). The magnetic field is formed only around moving electric charges, and its action also extends only to moving charges. Magnetic and electric fields are inseparable and form together a single electromagnetic field... Any change electric field leads to the appearance of a magnetic field and, conversely, any change in the magnetic field is accompanied by the appearance of an electric field. Electromagnetic field propagates at the speed of light, i.e. 300,000 km/s.

Graphical representation of the magnetic field. Graphically, the magnetic field is represented by magnetic lines of force, which are drawn so that the direction of the line of force at each point of the field coincides with the direction of the field forces; magnetic field lines are always continuous and closed. The direction of the magnetic field at each point can be determined using a magnetic needle. The north pole of the arrow is always set in the direction of the field forces. The end of the permanent magnet, from which the lines of force come out (Fig. 35, a), is considered to be the north pole, and the opposite end, which includes the lines of force, is the south pole (the lines of force passing inside the magnet are not shown). The distribution of lines of force between the poles of a flat magnet can be detected using steel filings sprinkled on a sheet of paper placed on the poles (Fig. 35, b). The magnetic field in the air gap between two parallel opposite poles of a permanent magnet is characterized by a uniform distribution of magnetic lines of force (Fig. 36)