The electromagnetic field is like. Electromagnetic fields

Electricity around us

Electromagnetic field (definition from TSB)- This is a special form of matter, through which the interaction between electrically charged particles is carried out. Based on this definition, it is not clear what is primary - the existence of charged particles or the presence of a field. It can only be due to the presence of an electromagnetic field that particles can receive a charge. Just like the chicken and egg story. The bottom line is that charged particles and an electromagnetic field are inseparable from each other and cannot exist without each other. Therefore, the definition does not give you and me the opportunity to understand the essence of the phenomenon of the electromagnetic field and the only thing that should be remembered is that it is special form of matter! The electromagnetic field theory was developed by James Maxwell in 1865.

What is an electromagnetic field? You can imagine that we live in an electromagnetic Universe, which is completely and completely permeated by an electromagnetic field, and various particles and substances, depending on their structure and properties, under the influence of the electromagnetic field acquire a positive or negative charge, accumulate it, or remain electrically neutral. Accordingly electro magnetic fields can be divided into two types: static, that is, emitted by charged bodies (particles) and inalienable from them, and dynamic, propagating in space, being torn off from the source that emitted it. A dynamic electromagnetic field in physics is represented in the form of two mutually perpendicular waves: electric (E) and magnetic (H).

The fact that electric field generated by variable magnetic field, and the magnetic field - alternating electric, leads to the fact that electric and magnetic alternating fields do not exist separately from each other. The electromagnetic field of stationary or uniformly moving charged particles is directly related to the particles themselves. With the accelerated motion of these charged particles, the electromagnetic field "detaches" from them and exists independently in the form electromagnetic waves without disappearing with the elimination of the source.

Sources of electromagnetic fields

Natural (natural) sources of electromagnetic fields

Natural (natural) sources of EMF are divided into the following groups:

Earth's magnetic field. The magnitude of the Earth's geomagnetic field varies over the earth's surface from 35 μT at the equator to 65 μT near the poles.

Electric field of the earth directed normally to the earth's surface, charged negatively with respect to upper layers atmosphere. Tension electric field at the Earth's surface is 120 ... 130 V / m and decreases with height approximately exponentially. Annual changes in the electric field are similar in nature throughout the Earth: the maximum voltage is 150 ... 250 V / m in January-February and the minimum one is 100 ... 120 V / m in June-July.

Atmospheric electricity Are electrical phenomena in the earth's atmosphere. In the air (link) there are always positive and negative electric charges - ions that arise under the action of radioactive substances, cosmic rays and ultraviolet radiation from the Sun. Earth negatively charged; there is a large potential difference between it and the atmosphere. The strength of the electrostatic field rises sharply during thunderstorms. The frequency range of atmospheric discharges is between 100 Hz and 30 MHz.

Extraterrestrial sources include radiation outside the Earth's atmosphere.

Biological electromagnetic background. Biological objects like others physical bodies, at temperatures above absolute zero, they emit EMF in the range of 10 kHz - 100 GHz. This is due to the chaotic movement of charges - ions, in the human body. The power density of such radiation in humans is 10 mW / cm2, which for an adult gives a total power of 100 W. The human body also emits EMFs at 300 GHz with a power density of about 0.003 W / m2.

Anthropogenic sources of electromagnetic fields

Anthropogenic sources are divided into 2 groups:

Low frequency radiation sources (0 - 3 kHz)

This group includes all systems for the production, transmission and distribution of electricity (power lines, transformer substations, power plants, various cable systems), home and office electrical and electronic equipment, including PC monitors, electric transport, railway transport and its infrastructure, as well as metro, trolleybus and tram transport.

Already today, the electromagnetic field on 18-32% of the territory of cities is formed as a result of automobile traffic. Electromagnetic waves generated by the movement of vehicles interfere with television and radio reception, and can also cause harmful effect on the human body.

High frequency radiation sources (3 kHz to 300 GHz)

This group includes functional transmitters - sources of an electromagnetic field for the purpose of transmitting or receiving information. These are commercial transmitters (radio, television), radiotelephones (auto and radiotelephones, CB radio, amateur radio transmitters, industrial radiotelephones), directional radio communications (satellite radio communications, ground relay stations), navigation (air traffic, shipping, radio hotspots), locators (air communication, shipping, transport locators, air transport control). This also includes various technological equipment using microwave radiation, variable (50 Hz - 1 MHz) and pulsed fields, household equipment(Microwave ovens), means of visual display of information on cathode-ray tubes (PC monitors, televisions, etc.). For scientific research in medicine, ultra-high-frequency currents are used. The electromagnetic fields arising from the use of such currents represent a certain occupational hazard, therefore it is necessary to take protective measures against their effects on the body.

The main man-made sources are:

A feature of irradiation in urban conditions is the impact on the population of both the total electromagnetic background (integral parameter) and strong EMF from individual sources (differential parameter).

Scientific and technological progress is accompanied by sharp increase the power of electromagnetic fields (EMF), created by man, which in some cases are hundreds and thousands of times higher than the level of natural fields.

The spectrum of electromagnetic waves includes waves of length from 1000 km to 0.001 microns and in frequency f from 3 × 10 2 to 3 × 10 20 Hz. The electromagnetic field is characterized by a set of vectors of electric and magnetic components. Different ranges of electromagnetic waves have a common physical nature, but differ in energy, nature of propagation, absorption, reflection and action on the environment, a person. The shorter the wavelength, the more energy the quantum carries.

The main characteristics of EMF are:

Electric field strength E, V / m.

Magnetic field strength N, A / m.

Energy flux density carried by electromagnetic waves I, W / m 2.

The relationship between them is determined by the dependency:

Energy connection I and frequencies f fluctuation is defined as:

where: f = s / l, a c = 3 × 10 8 m / s (speed of propagation of electromagnetic waves), h= 6.6 × 10 34 W / cm 2 (Planck's constant).

In space. the surrounding EMF source is divided into 3 zones (Fig. 9):

a) Near zone(induction), where there is no wave propagation, no energy transfer, and therefore the electric and magnetic components of the EMF are considered independently. R zone boundary< l/2p.

b) Intermediate zone(diffraction), where waves are superimposed on each other, forming peaks and standing waves. Zone boundaries l / 2p< R < 2pl. Основная характеристика зоны суммарная плотность потоков энергии волн.

v) Radiation area(wave) with the boundary R> 2pl. There is wave propagation, therefore, the characteristic of the radiation zone is the energy flux density, i.e. the amount of energy incident on a unit surface I(W / m 2).

Rice. 1.9... Zones of existence of an electromagnetic field

The electromagnetic field, with distance from radiation sources, attenuates in inverse proportion to the square of the distance from the source. In the induction zone, the electric field strength decreases inversely proportional to the distance to the third power, and the magnetic field decreases inversely proportional to the square of the distance.

By the nature of the impact on the human body, EMF is divided into 5 ranges:

Power frequency electromagnetic fields (EMP IF): f < 10 000 Гц.

Electromagnetic radiations of radio frequency range (EMR RF) f 10,000 Hz.

The electromagnetic fields of the radio-frequency part of the spectrum are divided into four sub-bands:

1) f 10,000 Hz to 3,000,000 Hz (3 MHz);

2) f from 3 to 30 MHz;

3) f from 30 to 300 MHz;

4) f 300 MHz to 300,000 MHz (300 GHz).

Sources of electromagnetic fields of industrial frequency are high voltage power lines, open switchgear, all Electricity of the net and devices powered by alternating current 50 Hz. The danger of exposure to lines increases with increasing voltage due to an increase in the charge concentrated on the phase. The electric field strength in areas where high-voltage power lines pass can reach several thousand volts per meter. Waves of this range are strongly absorbed by the soil and at a distance of 50-100 m from the line, the intensity drops to several tens of volts per meter. With the systematic exposure to EP, functional disturbances in the activity of the nervous and cardiovascular systems are observed. With an increase in the field strength in the body, persistent functional changes occur in the central nervous system. Along with the biological effect of an electric field between a person and a metal object, discharges can occur due to the body potential, which reaches several kilovolts if a person is isolated from the Earth.

Permissible levels of intensity of electric fields at workplaces are established by GOST 12.1.002-84 "Electric fields of industrial frequency". The maximum permissible level of intensity of the IF EMF is set at 25 kV / m. The admissible residence time in such a field is 10 minutes. Staying in the EMP of the inverter with a voltage of more than 25 kV / m without protective equipment is not allowed, and in the EMF of the inverter with a voltage of up to 5 kV / m it is allowed to stay during the whole working day. To calculate the permissible residence time in the electric drive at an intensity of more than 5 to 20 kV / m, inclusive, the formula is used T = (50/E) - 2, where: T- permissible time of stay in the PCh EMF, (hour); E- intensity of the electrical component of the PCh EMF, (kV / m).

Sanitary standards SN 2.2.4.723-98 regulate the remote control of the magnetic component of the PCh EMF at workplaces. Magnetic strength N should not exceed 80 A / m with an 8-hour stay in this field.

The intensity of the electrical component of the PCh EMF in residential buildings and apartments is regulated by SanPiN 2971-84 "Sanitary norms and rules for protecting the population from the effects of an electric field created by by air lines power transmission alternating current industrial frequency ". According to this document, the value E should not exceed 0.5 kV / m inside residential premises and 1 kV / m on the territory of urban development. The norms for the remote control of the magnetic component of the EMI of the frequency converter for residential and urban environments have not been developed at present.

EMP RF are used for heat treatment, metal smelting, radio communications, and medicine. Sources of EMF in industrial premises are lamp generators, in radio installations - antenna systems, in microwave ovens - energy leaks when the screen of the working chamber is broken.

RF EMR acting on the body causes the polarization of atoms and molecules of tissues, the orientation of polar molecules, the appearance of ion currents in tissues, and heating of tissues due to the absorption of EMF energy. This disrupts the structure of electrical potentials, the circulation of fluid in the cells of the body, the biochemical activity of molecules, and the composition of the blood.

The biological effect of RF EMR depends on its parameters: wavelength, intensity and mode of radiation (pulsed, continuous, intermittent), on the area of ​​the irradiated surface, duration of irradiation. Electromagnetic energy is partially absorbed by tissues and converted into heat, local heating of tissues and cells occurs. RF EMR has an adverse effect on the central nervous system, causes disturbances in neuro-endocrine regulation, changes in the blood, clouding of the lens of the eyes (only sub-range 4), metabolic disturbances.

Hygienic regulation of RF EMR is carried out in accordance with GOST 12.1.006-84 “Electromagnetic fields of radio frequencies. Permissible levels at workplaces and requirements for control. " The EMF levels at workplaces are controlled by measuring the intensity of the electrical and magnetic components in the 60 kHz-300 MHz frequency range, and the EMF energy flux density (PEF) in the 300 MHz-300 GHz frequency range, taking into account the time spent in the irradiation zone.

For EMF of radio frequencies from 10 kHz to 300 MHz, the intensity of the electric and magnetic components of the field is regulated depending on the frequency range: the higher the frequency, the lower the permissible value of the intensity. For example, the electrical component of the EMF for frequencies of 10 kHz - 3 MHz is 50 V / m, and for frequencies of 50 MHz - 300 MHz, only 5 V / m. In the frequency range 300 MHz - 300 GHz, the radiation energy flux density and the energy load created by it are regulated, i.e. the energy flux passing through a unit of the irradiated surface during the action. Maximum value the energy flux density should not exceed 1000 µW / cm 2. The residence time in such a field should not exceed 20 minutes. Staying in a field with a PES equal to 25 μW / cm 2 is allowed during an 8-hour work shift.

In urban and domestic environments, RF EMR is standardized in accordance with SN 2.2.4 / 2.1.8-055-96 "Electromagnetic radiation of radio frequency range". In residential premises, the PPE EMR RF should not exceed 10 μW / cm 2.

In mechanical engineering, magnetic-pulse and electro-hydraulic processing of metals with a low-frequency pulse current of 5-10 kHz is widely used (cutting and squeezing tubular blanks, stamping, punching holes, cleaning castings). Sources pulse magnetic the field in the workplace are open working inductors, electrodes, current-carrying buses. The pulsed magnetic field affects the metabolism in the tissues of the brain, the endocrine regulation systems.

Electrostatic field(ESP) is the field of stationary electric charges interacting with each other. ESP is characterized by tension E, that is, the ratio of the force acting in the field on a point charge to the value of this charge. ESP strength is measured in V / m. ESPs arise in power plants, in electrotechnical processes. ESP is used in electro-gas cleaning, when applying paints and varnishes... ESP has a negative effect on the central nervous system; those working in the ESP zone experience a headache, sleep disturbance, etc. In ESP sources, in addition to biological effects, aeroions pose a certain danger. The source of air ions is the corona, which appears on the wires under tension E> 50 kV / m.

Allowable tension levels ESP installed by GOST 12.1.045-84 “Electrostatic fields. Allowable Levels at Workplaces and Requirements for Conducting Control ". The permissible level of ESP tension is set depending on the time spent at the workplace. The remote control for the ESP intensity is set equal to 60 kV / m for 1 hour. When the ESP strength is less than 20 kV / m, the residence time in the ESP is not regulated.

Main characteristics laser radiation are: wavelength l, (μm), radiation intensity, determined by the energy or power of the output beam and expressed in joules (J) or watts (W): pulse duration (sec), pulse repetition rate (Hz) ... The main hazard criteria for a laser are its power, wavelength, pulse duration and exposure.

According to the degree of danger, lasers are divided into 4 classes: 1 - the output radiation is not dangerous for the eyes, 2 - direct and specularly reflected radiation is dangerous for the eyes, 3 - diffusely reflected radiation is dangerous for the eyes, 4 - diffusely reflected radiation is dangerous for the skin ...

The laser class according to the degree of hazard of the generated radiation is determined by the manufacturer. When working with lasers, personnel are exposed to harmful and hazardous production factors.

The group of physical harmful and dangerous factors during the operation of lasers includes:

Laser radiation (direct, scattered, specular or diffusely reflected),

The increased value of the voltage of the power supply of the lasers,

Dustiness of the air in the working area by products of interaction of laser radiation with the target, increased level of ultraviolet and infrared radiation,

Ionizing and electromagnetic radiation in working area, increased brightness of light from pulsed pump lamps and explosion hazard of laser pumping systems.

The personnel serving the lasers are exposed to chemically hazardous and harmful factors, such as ozone, nitrogen oxides and other gases due to the nature of the production process.

The effect of laser radiation on the body depends on the radiation parameters (power, wavelength, pulse duration, pulse repetition rate, exposure time and area of ​​the irradiated surface), the localization of the effect and the characteristics of the irradiated object. Laser radiation causes organic changes (primary effects) and specific changes in the body itself (secondary effects) in the irradiated tissues. Under the action of radiation, the irradiated tissues are rapidly heated, i.e. thermal burn. As a result of rapid heating up to high temperatures there is a sharp increase in pressure in the irradiated tissues, which leads to their mechanical damage... The effects of laser radiation on the body can cause functional disorders and even complete loss of vision. The nature of the damaged skin varies from mild to varying degrees of burns, up to necrosis. In addition to tissue changes, laser radiation causes functional changes in the body.

The maximum permissible exposure levels are regulated by Sanitary Norms and Rules for the Construction and Operation of Lasers 2392-81. The maximum permissible exposure levels are differentiated taking into account the operating mode of the lasers. For each operating mode, section of the optical range, the value of the remote control is determined according to special tables. Dosimetric control of laser radiation is carried out in accordance with GOST 12.1.031-81. The control measures the power density of continuous radiation, the energy density of pulsed and pulse-modulated radiation and other parameters.

Ultraviolet radiation - it is electromagnetic radiation invisible to the eye, which occupies an intermediate position between light and X-ray radiation. The biologically active part of UV radiation is divided into three parts: A with a wavelength of 400-315 nm, B with a wavelength of 315-280 nm and C 280-200 nm. UV rays have the ability to cause a photoelectric effect, luminescence, the development of photochemical reactions, and also have significant biological activity.

UV radiation is characterized by bactericidal and erythemal properties. Erythemal radiation power - it is a value that characterizes the beneficial effect of UV radiation on a person. The unit of erythemal radiation is Er, corresponding to a power of 1 W for a wavelength of 297 nm. The unit of erythemal illumination (irradiance) Er per square meter(Er / m2) or W / m2. Radiation dose Ner is measured in Er × h / m2, i.e. this is the irradiation of the surface for a certain time. The bactericidal activity of the UV radiation flux is measured in bact. Accordingly, the bactericidal irradiation is bact per m 2, and the dose of bact per hour per m 2 (bq × h / m 2).

Sources of UV radiation in production are an electric arc, autogenous flame, mercury-quartz burners and other temperature emitters.

Natural UV rays have a positive effect on the body. With a lack of sunlight, there is "light starvation", vitamin D deficiency, weakening of immunity, functional disorders nervous system... However, UV radiation from industrial sources can cause acute and chronic occupational eye diseases. Acute eye damage is called electrophthalmia. Erythema of the skin of the face and eyelids is often found. Chronic lesions include chronic conjunctivitis, lens cataracts, skin lesions (dermatitis, edema with blistering).

Standardization of UV radiation carried out in accordance with "Sanitary standards for ultraviolet radiation in industrial premises" 4557-88. When normalizing, the radiation intensity is set in W / m 2. At an irradiation surface of 0.2 m 2 for up to 5 minutes with a break of 30 minutes with a total duration of up to 60 minutes, the norm for UV-A is 50 W / m2, for UV-B is 0.05 W / m2 and for UV -C 0.01 W / m 2. With a total duration of irradiation of 50% of a work shift and a single irradiation of 5 min, the norm for UV-A is 10 W / m 2, for UV-B is 0.01 W / m 2 with an irradiation area of ​​0.1 m 2, and the irradiation is UV-C is not allowed.

Electromagnetic fields and radiation are all around us. It is enough to flip the switch - and the light comes on, turn on the computer - and you are on the Internet, dial the number on mobile phone- and you can communicate with distant continents. In fact, it was electrical devices created modern world as we know it. However, in recent times more and more often, the question is raised that the electromagnetic fields (EMF) generated by electrical equipment are harmful. Is it so? Let's try to figure it out.

Let's start with the definition. Electromagnetic fields, as you know from the school physics course, are a special feature. The key feature of such fields is the ability to interact in a certain way with bodies and particles that have an electric charge. As the name suggests, electromagnetic fields are a combination of magnetic and electric fields, and in this case they are so closely interconnected that they are considered a single whole. Features of interaction with charged objects are explained using

For the first time, electromagnetic fields were mathematically expressed in theory by Maxwell in 1864. Actually, it was he who revealed the indivisibility of the magnetic and electric fields. One of the consequences of the theory was the fact that any disturbance (change) of the electromagnetic field is the cause of the appearance of electromagnetic waves propagating in a vacuum from Calculations showed that light (all parts of the spectrum: infrared, visible, ultraviolet) is precisely an electromagnetic wave. In general, when classifying radiation by wavelength, they distinguish between X-rays, radio, etc.

The appearance of Maxwell's theory was preceded by the work of Faraday (in 1831) on research in a conductor moving or in a periodically changing magnetic field. Earlier, in 1819, H. Oersted noticed that if a compass is placed next to a conductor with a current, then its arrow deviates from the natural one, which made it possible to assume a direct connection between magnetic and electric fields.

All this indicates that any electrical device is a generator of electromagnetic waves. This property is especially pronounced for some specific devices and high-current circuits. Both the first and the second are now present in almost every home. Since EMF spreads not only in conductive materials, but also in dielectrics (for example, vacuum), a person is constantly in their zone of action.

If earlier, when there was only "Ilyich's lamp" in the room, the question did not bother anyone. Now everything is different: the measurement of the electromagnetic field is performed using special devices for measuring the field strength. Both components of the EMF are recorded in a certain frequency range (depending on the sensitivity of the device). The SanPiN document indicates the PDN ( allowable rate). At enterprises and large companies, PDN EMI checks are periodically performed. It should be noted that there are still no definitive results of studies on the effects of EMF on living organisms. Therefore, for example, when working with computers, it is recommended to organize 15-minute breaks after every hour - just in case ... Everything is explained quite simply: there is an EMF around the conductor, which means there is also an EMF. The equipment is completely safe when the power cord is unplugged.

Obviously, few people will dare to completely abandon the use of electrical equipment. However, you can additionally protect yourself by connecting household appliances to a grounded network, which allows the potential not to collect on the case, but to "drain" into the ground loop. Various extension cords, especially those wound in rings, amplify the EMI through mutual induction. And, of course, you should avoid placing several devices in close proximity at once.

Electromagnetic field

An electromagnetic field refers to the type of matter that occurs around moving charges. It consists of electric as well as magnetic fields. Their existence is interconnected, since they cannot exist separately and independently of each other, because one field gives rise to another.

Now let's try to approach the topic of the electromagnetic field in more detail. From the definition, it can be concluded that in the event of a change in the electric field, there are prerequisites for the occurrence of a magnetic field. And since the electric field tends to change over time and cannot be called invariable, the magnetic field is also variable.

When you change one field, another is generated. And no matter what the subsequent field will be, the source will be the previous field, that is, a conductor with current, and not its original source.

And even if the current in the conductor is turned off, the electromagnetic field will not disappear anywhere, but will continue to exist and will spread in space.

Properties of electromagnetic waves

Maxwell's theory. Vortex electric field

James Clerk Maxwell, a famous British physicist, wrote a work in 1857 in which he provided evidence that fields such as electric and magnetic are closely related.

According to his theory, it followed that an alternating magnetic field has the ability to create such a new electric field, which differs from the previous electric field created with the help of a current source, since this new electric field is vortex.

And here you and I see that a vortex electric field is a field in which the lines of force are closed. That is, it should be noted that the electric field has the same closed lines as the magnetic field.

From this it follows that an alternating magnetic field is capable of creating a vortex electric field, and a vortex electric field has the ability to make charges move. And as a result, we get an induction electric current. It follows from Maxwell's work that such fields as electric and magnetic coexist closely with each other.

That is, for the existence of a magnetic field, a moving electric charge is required. Well, the electric field is created due to the resting electric charge. There is such a transparent relationship between the fields. From this we can draw another conclusion that in different systems countdown can be observed different kinds fields.

If we follow Maxwell's theory, then we can summarize that alternating electric and magnetic fields are not able to exist separately, because when the magnetic field changes, it generates an electric field, and a changing electric field generates a magnetic one.

Natural sources of electromagnetic fields

For a modern person, it is not a secret that the electromagnetic fields, although they remain invisible to our eyes, but surround us everywhere.

Natural sources of EMF include:

First, it is the permanent electric and magnetic field of the Earth.
Secondly, such sources include radio waves that convert such space sources like the sun, stars, etc.
Thirdly, these sources are also atmospheric processes such as lightning discharges, etc.

Anthropogenic (artificial) sources of electromagnetic fields

except natural sources emergence of EMF, they also arise due to anthropogenic sources. These sources include X-rays, which are used in medical institutions. They are also used to transmit information using various radio stations, mobile stations and also TV antennas. And the electricity that is in each outlet also generates an EMF, but it is true, of a lower frequency.

Impact of EMF on human health

Modern society currently does not think of its own life, without such benefits of civilization as the presence of various household appliances, computers, mobile communications. They, of course, make our life easier, but they create electromagnetic fields around us. Naturally, we cannot see EMF, but they surround us everywhere. They are present in our homes, at work, and even in transport.

We can safely say that modern man lives in a continuous electromagnetic field, which, unfortunately, has a huge impact on human health. With prolonged exposure to the electromagnetic field on the human body, such unpleasant symptoms as chronic fatigue, irritability, disturbed sleep, attention and memory appear. Such prolonged exposure to EMF can cause a person's headache, infertility, disturbances in the functioning of the nervous and cardiac systems, as well as the appearance of oncological diseases.