Electromagnetic field, special shape matter. Through electro magnetic field interaction occurs between charged particles.
The behavior of the electromagnetic field is studied by classical electrodynamics. The electromagnetic field is described by Maxwell's Equations, which relate the quantities characterizing 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; at accelerated movement particles, the electromagnetic field “breaks away” from them and exists independently in the form of electromagnetic waves.
From Maxwell's equations it follows that an alternating electric field generates a magnetic field, and an alternating magnetic field generates an electric one, therefore 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 field 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.
The electromagnetic field in a vacuum, that is, in a free state, not associated with particles of matter, exists in the form electromagnetic waves, and propagates in emptiness 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 tension electric field E and magnetic field induction IN. Electrical induction values are also used to describe the electromagnetic field in a medium D and magnetic field strength N. In matter, as well as in the presence of very strong gravitational fields, that is, near very large masses substances, the speed of propagation of the electromagnetic field is less than 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 upon transition from one inertial system reference to another in accordance with 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. Electromagnetic field energy density = 1/2(ED+BH).
An electromagnetic field propagates in space. The energy flux density of the electromagnetic field is determined by the Poynting vector S=, unit of measurement W/m2. 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 = S/s 2 = /s 2.
At high frequencies of the electromagnetic field, its quantum properties and the electromagnetic field can be considered as a flow of field quanta - photons. In this case, the electromagnetic field is described
Details Category: Electricity and magnetism Published 06/05/2015 20:46 Views: 11962Under certain conditions, alternating electric and magnetic fields can generate each other. They form an electromagnetic field, which is not their totality at all. This is a single whole in which these two fields cannot exist without each other.
From the history
The experiment of the Danish scientist Hans Christian Oersted, carried out in 1821, showed that electricity generates a magnetic field. In turn, a changing magnetic field can generate electric current. This has been proven English physicist Michael Faraday, who discovered the phenomenon in 1831 electromagnetic induction. He is also the author of the term “electromagnetic field”.
At that time, Newton's concept of long-range action was accepted in physics. It was believed that all bodies act on each other through the void at an infinitely high speed (almost instantly) and at any distance. It was assumed that electric charges interact In a similar way. Faraday believed that emptiness does not exist in nature, and interaction occurs with terminal speed through some material environment. This medium for electric charges is electromagnetic field. And it travels at a speed equal to the speed of light.
Maxwell's theory
Combining the results previous studies, English physicist James Clerk Maxwell created in 1864 electromagnetic field theory. According to it, a changing magnetic field generates a changing electric field, and an alternating electric field generates an alternating magnetic field. Of course, first one of the fields is created by a source of charges or currents. But in the future, these fields can already exist independently of such sources, causing each other to appear. That is, electric and magnetic fields are components of a single electromagnetic field. And every change in one of them causes the appearance of another. This hypothesis forms the basis of Maxwell's theory. The electric field generated by the magnetic field is a vortex. Its lines of force are closed.
This theory is phenomenological. This means that it is created based on assumptions and observations, and does not consider the cause of electric and magnetic fields.
Properties of the electromagnetic field
An electromagnetic field is a combination of electric and magnetic fields, therefore at each point in its space it is described by two main quantities: the electric field strength E and magnetic field induction IN .
Since the electromagnetic field is the process of converting an electric field into a magnetic field, and then magnetic into electric, its state is constantly changing. Propagating in space and time, it forms electromagnetic waves. Depending on the frequency and length, these waves are divided into radio waves, terahertz radiation, infrared radiation, visible light, ultraviolet radiation, x-rays and gamma rays.
The vectors of intensity and induction of the electromagnetic field are mutually perpendicular, and the plane in which they lie is perpendicular to the direction of propagation of the wave.
In the theory of long-range action, the speed of propagation of electromagnetic waves was considered infinitely large. However, Maxwell proved that this was not the case. In a substance, electromagnetic waves propagate at a finite speed, which depends on the dielectric and magnetic permeability of the substance. Therefore, Maxwell's Theory is called the theory of short-range action.
Maxwell's theory was confirmed experimentally in 1888. German physicist Heinrich Rudolf Hertz. He proved that electromagnetic waves exist. Moreover, he measured the speed of propagation of electromagnetic waves in a vacuum, which turned out to be equal to the speed of light.
IN integral form this law looks like this:
Gauss's law for magnetic field
The flux of magnetic induction through a closed surface is zero.
The physical meaning of this law is that in nature there is no magnetic charges. The poles of a magnet cannot be separated. The magnetic field lines are closed.
Faraday's Law of Induction
A change in magnetic induction causes the appearance of a vortex electric field.
,
Magnetic field circulation theorem
This theorem describes the sources of the magnetic field, as well as the fields themselves created by them.
Electric current and changes in electrical induction generate a vortex magnetic field.
,
,
E– electric field strength;
N– magnetic field strength;
IN- magnetic induction. This is a vector quantity that shows the force with which the magnetic field acts on a charge of magnitude q moving with speed v;
D – electrical induction, or electrical displacement. Represents vector quantity, equal to the amount tension vector and polarization vector. Polarization is caused by the displacement of electric charges under the influence of an external electric field relative to their position when there is no such field.
Δ - operator Nabla. The action of this operator on a specific field is called the rotor of this field.
Δ x E = rot E
ρ - density of external electric charge;
j- current density - a value showing the strength of the current flowing through a unit area;
With– speed of light in vacuum.
The study of the electromagnetic field is a science called electrodynamics. She considers its interaction with bodies that have an electric charge. This interaction is called electromagnetic. Classical electrodynamics only describes continuous properties electromagnetic field using Maxwell's equations. Modern quantum electrodynamics believes that the electromagnetic field also has discrete (discontinuous) properties. And so electromagnetic interaction occurs with the help of indivisible particles-quanta that have no mass and charge. The electromagnetic field quantum is called photon .
Electromagnetic field around us
An electromagnetic field is formed around any conductor carrying alternating current. Sources of electromagnetic fields are power lines, electric motors, transformers, urban electric transport, railway transport, electrical and electronic household appliances - televisions, computers, refrigerators, irons, vacuum cleaners, radiotelephones, mobile phones, electric shavers - in a word, everything related to consumption or transmission of electricity. Powerful sources of electromagnetic fields are television transmitters, antennas of cellular telephone stations, radar stations, microwave ovens, etc. And since there are quite a lot of such devices around us, electromagnetic fields surround us everywhere. These fields affect environment and man. This is not to say that this influence is always negative. Electric and magnetic fields have existed around humans for a long time, but the power of their radiation a few decades ago was hundreds of times lower than today.
Before a certain level electromagnetic radiation can be safe for humans. Thus, in medicine, low-intensity electromagnetic radiation is used to heal tissues, eliminate inflammatory processes, and have an analgesic effect. UHF devices relieve spasms of the smooth muscles of the intestines and stomach, improve metabolic processes in the body's cells, reducing capillary tone, and lower blood pressure.
But strong electromagnetic fields cause disruptions in the functioning of the human cardiovascular, immune, endocrine and nervous systems, and can cause insomnia, headaches, and stress. The danger is that their impact is almost invisible to humans, and disturbances occur gradually.
How can we protect ourselves from the electromagnetic radiation surrounding us? It is impossible to do this completely, so you need to try to minimize its impact. First of all, you need to arrange household appliances in such a way that they are located away from the places where we are most often. For example, don't sit too close to the TV. After all, the further the distance from the source of the electromagnetic field, the weaker it becomes. Very often we leave the device plugged in. But the electromagnetic field disappears only when the device is disconnected from the electrical network.
Natural electromagnetic fields also affect human health - cosmic radiation, Earth's magnetic field.
1. Introduction. Subject of study in valeology.
3. Main sources of electromagnetic field.
5. Methods of protecting human health from electromagnetic influence.
6. List of materials and literature used.
1. Introduction. Subject of study in valeology.
1.1 Introduction.
Valeology - from lat. "valeo" - "hello" - scientific discipline, studying 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 averaged 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 being accumulated, and practical research is being actively conducted. There is a gradual transition from the status of a scientific discipline to the status of an independent science.
1.2 Subject of study in valeology.
The subject of study in valeology is the individual health of a healthy person and the factors influencing it. Also, valeology deals with 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 experts from 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 life forms, characterized by variability over relatively long time periods and practical staticity over short ones.
3. Adaptation – the ability of life forms to adapt to changing conditions of existence and overloads. In case of adaptation disorders or too sudden and radical changes in conditions, maladjustment occurs - stress.
4. Phenotype is a combination of environmental factors that influence the development of a living organism. Also, the term “phenotype” characterizes a set of features of the development and physiology of an organism.
5. Genotype is a combination of hereditary factors that influence the development of a living organism, being 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 specific organism.
Health (as defined by WHO).
2. Electromagnetic field, its types, characteristics and classification.
2.1 Basic definitions. Types of electromagnetic field.
An electromagnetic field is a special form of matter through which interaction between electrically charged particles occurs.
Electric field – created by electric charges and charged particles in space. The picture shows a picture power lines(imaginary lines used to visually represent fields) electric field for two charged particles at rest:
Magnetic field - created by the movement of electric charges along a conductor. The picture of the field lines for a single conductor is shown in the figure:
The physical reason for the existence of an 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 the carrier (charged particle).
However, with the accelerated movement of carriers, the electromagnetic field “breaks off” 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 (movement of carriers - electrons) in the antenna emitting them disappears).
2.2 Basic characteristics of the electromagnetic field.
The electric field is characterized by the electric field strength (designation “E”, SI dimension – V/m, vector). The magnetic field is characterized by the magnetic field strength (designation “H”, SI dimension – A/m, vector). The module (length) of the vector is usually measured.
Electromagnetic waves are characterized by wavelength (designation "(", SI dimension - m), their emitting source - 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 (designation “B”, SI dimension - T) can also be used as a characteristic of the magnetic field.
2.3 Classification of electromagnetic fields.
The most commonly used is the so-called “zonal” classification of electromagnetic fields according to the degree of distance 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 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 quickly decreases (proportional to the square or cube of the distance to the source). In this zone the generated electromagnetic wave is not yet fully formed.
The “far” zone is the zone of the formed electromagnetic wave. Here the field strength decreases in inverse proportion to the distance to the source. In this zone, the experimentally determined relationship between the electric and magnetic field strengths is valid:
where 377 is a constant, wave impedance of vacuum, Ohm.
Electromagnetic waves are usually classified by frequency:
|Name |Borders |Name |Borders |
| frequency | range | wave | range |
|range | |range | |
| Extremely low, | Hz | Decamegameter | Mm |
|Ultra-low, SLF | Hz | Megameter | Mm |
|Infra-low, INF | KHz | Hecto-kilometer | |
|Very low, VLF | KHz | Myriameter | km |
|Low frequencies, LF| KHz|Kilometer | km |
|Average, midrange | MHz | Hectometer | km |
|High, HF | MHz | Decameter | m |
|Very high, VHF| MHz|Meter | m |
|Ultrahigh, UHF| GHz |Decimeter | m |
|Ultra-high, microwave | GHz | Centimeter | cm |
| Extremely high, | GHz|Millimeter | mm |
|Hyperhigh, HHF | |Decimmillimeter | mm |
Usually only the electric field strength E is measured. At frequencies above 300 MHz, the wave energy flux density, or the Pointing vector (designation “S”, SI dimension - W/m2) is sometimes measured.
3. The main sources of the electromagnetic field.
The main sources of the electromagnetic field can be identified:
Power lines.
Electrical wiring (inside buildings and structures).
Household electrical appliances.
Personal computers.
TV and radio broadcasting stations.
Satellite and cellular communications (devices, repeaters).
Electric transport.
Radar installations.
3.1 Power lines (PTL).
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 within wide limits, depending on its electrical load. The standards establish the boundaries of sanitary protection zones near power lines (according to SN 2971-84):
|Operating voltage |330 and below |500 |750 |1150 |
|Power lines, kV | | | | |
|Size |20 |30 |40 |55 |
| sanitary-protective | | | | |
|zones, m | | | | |
(in fact, the boundaries of the sanitary protection zone are established along the boundary line of maximum electric field strength, equal to 1 kV/m, farthest from the wires).
3.2 Electrical wiring.
Electrical wiring includes: power supply cables for building life support systems, current distribution wires, as well as distribution boards, power boxes and transformers. Electrical wiring is the main source of industrial frequency electromagnetic fields in residential premises. In this case, the level of 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. In this case, the radiation level varies within wide limits depending on the model, device design and specific operating mode. 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 operation of the device. The electric field strength near electrical household appliances does not exceed tens of V/m.
The table below shows the maximum permissible levels magnetic induction for the most powerful magnetic field sources among household electrical appliances:
|Device |Interval of maximum permissible |
| |magnetic induction values, µT|
|Coffee maker | |
|Washing machine | |
|Iron | |
|Vacuum cleaner | |
|Electric stove | |
| Daylight lamp (fluorescent lamps LTB, | |
| Electric drill (electric motor | |
| power W) | |
| Electric mixer (electric motor power | |
| W) | |
|TV | |
|Microwave oven (induction, microwave) | |
3.4 Personal computers.
The main source of adverse effects on the health of a computer user is the visual display facility (VDI) of the monitor. In most modern monitors, the CVO is a cathode ray tube. The table lists the main factors affecting the health of SVR:
|Ergonomic |Factors of electromagnetic influence |
| |fields of a cathode ray tube |
| Significant reduction in contrast | Electromagnetic field in frequency |
| reproduced image in the | MHz range. |
| external illumination of the screen with direct rays | |
|light. | |
|Mirror reflection rays of light from |Electrostatic charge on the surface |
|screen surface (glare). |monitor screen. |
|Cartoon character |Ultraviolet radiation (range |
|image reproduction |wavelength nm). |
|(high frequency continuous update | |
| Discrete nature of the image | Infrared and X-ray |
|(subdivision into points). |ionizing radiation. |
In the future, as the main factors of the impact of SVO on health, we will consider only the factors of exposure to the electromagnetic field of a cathode ray tube.
In addition to the monitor and system unit, a personal computer may also include a large number of other devices (such as printers, scanners, surge protectors, etc.). All these devices operate using electric current, which means 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 assembled. |. |
| I/O devices (printers, | Hz. |
|scanners, disk drives, etc.). | |
|Uninterruptible power supplies, |. |
|line filters and stabilizers. | |
The electromagnetic field of personal computers has a very 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). Considering the fact that personal computers are now actively used in all sectors of human activity, their impact on human health is subject to careful study and control.
3.5 Television and radio transmitting stations.
Russia currently hosts a significant number of radio broadcasting stations and centers of various affiliations.
Transmitting stations and centers are located in specially designated areas and can occupy fairly large areas (up to 1000 hectares). In 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 transmitting antenna and a feed line supplying the broadcast signal.
The electromagnetic field emitted by the antennas of radio broadcasting centers has a complex spectral composition and individual distribution of strengths depending on the configuration of the antennas, the terrain and the architecture of the adjacent buildings. Some average data for various types of radio broadcasting centers are presented in the table:
|Type |Normed |Normed |Features. |
|broadcast|tension |tension | |
|go center. | electric | magnetic field, | |
| |fields, V/m. |A/m. | |
| LW - radio stations | 630 | 1.2 | Highest tension |
|(frequency | | |field is achieved at |
|KHz, | | |distances less than 1 length |
|power | | |waves from the radiating |
|transmitters 300 –| | | antennas. |
|500 kW). | | | |
|CB – radio stations |275 |<нет данных>| Near the antenna (on |
|(frequency, | | |some observed |
|power | | |decrease in tension |
|50 transmitters - | | |electric field. |
|200 kW). | | | |
| HF radio stations | 44 | 0.12 | Transmitters can be |
|(frequency | | | located on |
|MHz, | | |densely built up |
|power | | | territories, as well as | |
|10 transmitters – | | | roofs of residential buildings. |
|100 kW). | | | |
|Television |15 |<нет данных>| Transmitters usually |
|radio broadcast| | | located at heights |
|e centers (frequencies | | |more than 110 m above average |
| MHz, | | |building level. |
|power | | | |
|100 transmitters | | | |
|KW – 1MW and | | | |
|more). | | | |
3.6 Satellite and cellular communications.
3.6.1 Satellite communications.
Satellite communication systems consist of a transmitting station on Earth and travelers - repeaters in orbit. Satellite communication transmitting stations emit a narrowly directed wave beam, the energy flux density of which reaches hundreds of W/m. Satellite communication systems create high electromagnetic field strengths at significant distances from the antennas. For example, a 225 kW station operating at a frequency of 2.38 GHz creates an energy flux density of 2.8 W/m2 at a distance of 100 km. Energy dissipation relative to the main beam is very small and occurs most of all in the area where the antenna is directly located.
3.6.2 Cellular communications.
Cellular radiotelephony is one of the most rapidly developing telecommunication systems today. 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 electromagnetic fields. The system uses the principle of dividing the coverage area into zones, or so-called “cells,” with a radius of km. The table below presents the main characteristics of the cellular communication systems operating in Russia:
|Name|Working |Working |Maximum |Maximum |Radius |
|systems, |range |range |radiated |radiated |coverings |
|principle |basic |mobile |power |power |unit |
|transmission |stations, |devices,|basic |mobile |basic |
|information. |MHz. |MHz. | stations, W. |devices, |stations, |
| | | | |Tue |km. |
|NMT450. | |
|Analog. |5] |5] | | | |
|AMPS. |||100 |0.6 | |
|Analog. | | | | | |
|DAMPS (IS – |||50 |0.2 | |
|136). | | | | | |
|Digital. | | | | | |
|CDMA. |||100 |0.6 | |
|Digital. | | | | | |
|GSM – 900. |||40 |0.25 | |
|Digital. | | | | | |
|GSM – 1800. | |
|Digital. |0] |5] | | | |
The radiation intensity of the base station is determined by the load, that is, the presence of owners cell phones 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 station load is almost zero. The intensity of radiation from mobile devices depends to a large extent on the state of the communication channel “mobile radiotelephone – base station” (the greater the distance from the base station, the higher the intensity of radiation from the device).
3.7 Electric transport.
Electric transport (trolleybuses, trams, metro trains, etc.) is powerful source electromagnetic field in the frequency range Hz. In this case, in the vast majority of cases, the role of the main emitter is played by the traction electric motor (for trolleybuses and trams, aerial pantographs compete with the electric motor in terms of the intensity of the emitted electric field). The table shows data on the measured value of magnetic induction for some types of electric transport:
|Mode of transport and type |Average value | Maximum value |
| current consumption. |magnetic induction, µT. | Magnetic magnitude |
| | |induction, µT. |
|Commuter electric trains.|20 |75 |
|Electric transport with |29 |110 |
|drive direct current | | |
|(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 intermittency of the radiation. Temporary intermittency of radiation is also observed, due to the cyclic operation of the radar on 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 special character radiation they can create zones on the ground with high density energy flow (100 W/m2 or more).
4. The influence of the electromagnetic field on individual human health.
The human body always reacts to an external electromagnetic field. Due to different wave composition and other factors, the electromagnetic field of different sources affects human health in different ways. As a result, in this section The impact of various sources on health will be considered separately. However, the field, which is sharply dissonant with the natural electromagnetic background artificial sources in almost all cases it affects the health of people in the area of its influence Negative influence.
Extensive research into the influence of electromagnetic fields on health began in our country in the 60s. It was found that the human nervous system is sensitive to electromagnetic influence, and also that the field has a so-called information effect when exposed to a person at intensities below the threshold value thermal effect(the magnitude of the field strength at which its thermal effect begins to appear).
The table below shows the most common complaints about the deterioration of the health of people in the area of exposure to fields from various sources. The sequence and numbering of sources in the table corresponds to their sequence and numbering adopted in Section 3:
|Source |The most common complaints. |
|electromagnetic | |
|1. Lines |Short-term irradiation (on the order of several minutes) can|
| power transmission lines (power lines). |lead to a negative reaction only in those who are particularly sensitive |
| | people or patients with certain types of allergies |
| | diseases. Prolonged exposure usually leads to |
| |various pathologies of the cardiovascular and nervous systems |
| |(due to subsystem imbalance nervous regulation). When |
| |ultra-long (about 10-20 years) continuous irradiation |
| |possible (according to unverified data) the development of some |
| |oncological diseases. |
|2. Internal |Current data on complaints of deterioration |
|electrical wiring of buildings|health related directly to the work of internal |
| and buildings. |there are no electrical networks. |
|3. Household | There are unverified data on skin complaints, |
| electrical appliances. |cardiovascular and nervous pathologies in long-term |
| | systematic use of old microwave ovens |
| |models (up to 1995). There are also similar |
| | data regarding application microwave ovens everyone |
| |models in production conditions (for example, for heating |
| | food in a cafe). In addition to microwave ovens, there is data on |
| | negative impact on the health of people with televisions |
| | as a visualization device, a cathode ray tube. |
Scientific and technological progress is accompanied by a sharp increase in 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.
Range electromagnetic vibrations includes wavelengths from 1000 km to 0.001 µm and by frequency f from 3×10 2 to 3×10 20 Hz. The electromagnetic field is characterized by a set of vectors of electrical and magnetic components. Different ranges of electromagnetic waves have a common physical nature, but differ in energy, nature of propagation, absorption, reflection and effect on the environment and humans. 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/m2.
The connection between them is determined by the dependence:
Energy connection I and frequencies f vibrations 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. There are 3 zones surrounding the EMF source (Fig. 9):
A) Near zone(induction), where there is no wave propagation, no energy transfer, and therefore the electrical and magnetic components of EMF are considered independently. Zone R boundary< l/2p.
b) Intermediate zone(diffraction), where waves overlap each other, forming maxima and standing waves. Zone boundaries l/2p< R < 2pl. Основная характеристика зоны суммарная плотность потоков энергии волн.
V) Radiation zone(wave) with the boundary R > 2pl. There is wave propagation, therefore the characteristic of the radiation zone is the energy flux density, i.e. amount of energy incident per unit surface I(W/m2).
 |
Rice. 1.9. Zones of electromagnetic field existence
The electromagnetic field, as it moves away from the radiation sources, attenuates inversely proportional to the square of the distance from the source. In the induction zone, the electric field strength decreases in inverse proportion to the distance to the third power, and the magnetic field decreases in inverse proportion to the square of the distance.
Based on the nature of their impact on the human body, EMFs are divided into 5 ranges:
Power frequency electromagnetic fields (PFEMF): f < 10 000 Гц.
Electromagnetic radiation in the radio frequency range (RF EMR) f 10,000 Hz.
Electromagnetic fields of the radio frequency part of the spectrum are divided into four subranges:
1) f from 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 from 300 MHz to 300,000 MHz (300 GHz).
Sources of industrial-frequency electromagnetic fields are high-voltage power lines, open distribution devices, all electrical networks and devices powered by 50 Hz alternating current. 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 in this range are strongly absorbed by the soil and at a distance of 50-100 m from the line, the voltage drops to several tens of volts per meter. With systematic exposure to EP, functional disturbances in the activity of the nervous and cardiovascular systems are observed. With increasing field strength in the body, persistent functional changes occur in the central nervous system. Along with biological effect electric field between a person and a metal object, discharges can occur due to the body potential, which reaches several kilovolts if the person is isolated from the Earth.
Permissible levels of electric field strength at workplaces are established by GOST 12.1.002-84 “Electric fields of industrial frequency”. The maximum permissible level of EMF IF voltage is set at 25 kV/m. The permissible time spent in such a field is 10 minutes. Staying in an EMF IF with a voltage of more than 25 kV/m without protective equipment is not allowed, and staying in an EMF IF with a voltage of up to 5 kV/m is allowed throughout the entire working day. To calculate the permissible time of stay in the ED at voltages above 5 to 20 kV/m inclusive, the formula is used T = (50/E) - 2, where: T- permissible time of stay in the EMF IF, (hour); E- intensity of the electrical component of the EMF IF, (kV/m).
Sanitary standards SN 2.2.4.723-98 regulate the maximum permissible limits of the magnetic component of the EMF IF in the workplace. Magnetic component strength N should not exceed 80 A/m during an 8-hour stay in the conditions of this field.
The intensity of the electrical component of the EMF IF in residential buildings and apartments is regulated by SanPiN 2971-84 “Sanitary standards and rules for protecting the population from the effects of the 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 in urban areas. The MPL standards for the magnetic component of EMF IF for residential and urban environments have not currently been developed.
RF EMR is used for heat treatment, metal smelting, radio communications, and medicine. The 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 damaged.
EMF RF exposure to the body causes polarization of atoms and molecules of tissues, orientation of polar molecules, the appearance of ionic currents in tissues, and heating of tissues due to the absorption of EMF energy. It breaks the structure electrical potentials, fluid circulation in the cells of the body, biochemical activity of molecules, blood composition.
The biological effect of RF EMR depends on its parameters: wavelength, intensity and mode of radiation (pulsed, continuous, intermittent), the area of the irradiated surface, and the 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, causing disturbances in neuroendocrine regulation, changes in the blood, clouding of the lens of the eyes (exclusively 4 subbands), metabolic disorders.
Hygienic standardization 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 monitoring." EMF levels at workplaces are controlled by measuring the intensity of the electrical and magnetic components in the frequency range 60 kHz-300 MHz, and in the frequency range 300 MHz-300 GHz the energy flux density (PED) of EMF, taking into account the time spent in the irradiation zone.
For EMF radio frequencies from 10 kHz to 300 MHz, the strength of the electric and magnetic components of the field is regulated depending on the frequency range: the higher the frequencies, the lower the permissible value of the strength. For example, the electrical component of EMF for frequencies 10 kHz - 3 MHz is 50 V/m, and for frequencies 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 it creates are regulated, i.e. energy flow passing through a unit of irradiated surface during the action. The maximum value of energy flux density should not exceed 1000 μW/cm2. The time spent in such a field should not exceed 20 minutes. Staying in the field in a PES equal to 25 μW/cm 2 is allowed during an 8-hour work shift.
In urban and domestic environment RF EMR regulation is carried out in accordance with SN 2.2.4/2.1.8-055-96 “Electromagnetic radiation in the radio frequency range”. In residential premises, the RF EMR PES 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 crimping tubular blanks, stamping, cutting holes, cleaning castings). Sources pulse magnetic The fields at the workplace are open working inductors, electrodes, and current-carrying busbars. A pulsed magnetic field affects metabolism in brain tissue, endocrine systems regulation.
Electrostatic field(ESP) is a 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 magnitude of this charge. ESP intensity is measured in V/m. ESPs arise in power plants, in electrotechnological processes. ESP is used in electrical gas cleaning and when applying paint and varnish coatings. ESP has a negative effect on the central nervous system; workers in the zone develop ESP headache, sleep disturbance, etc. In ESP sources, in addition to biological effects, air ions pose a certain danger. The source of air ions is the corona that appears on the wires at voltage E>50 kV/m.
Acceptable tension levels ESPs are installed by GOST 12.1.045-84 “ Electrostatic fields. Permissible levels at workplaces and requirements for monitoring.” The permissible level of ESP tension is established depending on the time spent at the workplace. The ESP voltage level is set to 60 kV/m for 1 hour. When the ESP voltage is less than 20 kV/m, the time spent 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 frequency (Hz) . The main criteria for the danger of a laser are its power, wavelength, pulse duration and radiation exposure.
According to the degree of danger, lasers are divided into 4 classes: 1 - output radiation is not dangerous to the eyes, 2 - direct and specularly reflected radiation is dangerous to the eyes, 3 - diffusely reflected radiation is dangerous to the eyes, 4 - diffusely reflected radiation is dangerous to the skin. .
The laser class according to the degree of danger of the generated radiation is determined by the manufacturer. When working with lasers, personnel are exposed to harmful and dangerous production factors.
To the group of physical harmful and hazardous factors when operating lasers include:
Laser radiation (direct, diffuse, specular or diffusely reflected),
Increased laser power supply voltage,
Dustiness of the air in the working area due to the products of interaction of laser radiation with the target, increased level ultraviolet and infrared radiation,
Ionizing and electromagnetic radiation V work area, increased brightness of light from pulsed pump lamps and the risk of explosion of laser pumping systems.
Personnel servicing lasers are exposed to hazardous chemicals 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, irradiation time and irradiated surface area), localization of the effect and characteristics of the irradiated object. Laser radiation causes organic changes in the irradiated tissues (primary effects) and specific changes in the body itself (secondary effects). When exposed to radiation, rapid heating of the irradiated tissue occurs, i.e. thermal burn. As a result of rapid heating 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 burns, up to necrosis. In addition to tissue changes, laser radiation causes functional changes in the body.
Maximum permissible levels of exposure are regulated by “Sanitary norms and rules for the design and operation of lasers” 2392-81. The maximum permissible levels of irradiation are differentiated taking into account the operating mode of the lasers. For each operating mode, section of the optical range, the remote control value is determined using special tables. Dosimetric monitoring of laser radiation is carried out in accordance with GOST 12.1.031-81. When monitoring, the power density of continuous radiation, the energy density of pulsed and pulse-modulated radiation and other parameters are measured.
Ultraviolet radiation - This is electromagnetic radiation invisible to the eye, occupying 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 bactericidal and erythemal properties. Erythemal radiation power - this is a quantity characterizing beneficial effect UV radiation per person. The unit of erythemal radiation is taken to be Er, corresponding to a power of 1 W for a wavelength of 297 nm. Unit of erythemal illumination (irradiance) Er per square meter(Er/m2) or W/m2. Radiation dose Ner is measured in Er×h/m 2, i.e. this is the irradiation of the surface for certain time. The bactericidal power of the UV radiation flux is measured in bact. Accordingly, the bactericidal irradiation is bact per m 2, and the dose is bact per hour per m 2 (bq × h/m 2).
Sources of UV radiation in production are electric arc, autogenous flame, mercury-quartz burners and other temperature emitters.
Natural UV rays have positive influence on the body. In case of shortage sunlight“light starvation” occurs, vitamin D deficiency, weakened immunity, functional disorders nervous system. At the same time, UV radiation from industrial sources can cause acute and chronic occupational eye diseases. Acute lesion eye is called electroophthalmia. Erythema of the skin of the face and eyelids is often detected. TO chronic lesions Chronic conjunctivitis, lens cataract, skin lesions (dermatitis, swelling with blistering) should be included.
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. With an irradiation surface of 0.2 m2 for up to 5 minutes with a break of 30 minutes for a total duration of up to 60 minutes, the norm for UV-A is 50 W/m2, for UV-B 0.05 W/m2 and for UV -C 0.01 W/m2. At total duration irradiation of 50% of the work shift and a single irradiation of 5 min, the norm for UV-A is 10 W/m2, for UV-B 0.01 W/m2 with an irradiation area of 0.1 m2, and irradiation with UV-C not allowed.
Electromagnetic fields and radiation surround us everywhere. Just 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 is electrical devices created modern world as we know it. However, in Lately The question is increasingly being raised that electromagnetic fields (EMFs) generated by electrical equipment are harmful. Is it so? Let's try to figure it out.
Let's start with a definition. Electromagnetic fields, as is known from school course physicists represent a special Key Feature similar fields is the ability to interact in a certain way with bodies and particles that have electric charge. As the name suggests, electromagnetic fields are a combination of magnetic and electric fields, and in in this case they are so closely interconnected that they are considered a single whole. Features of interaction with charged objects are explained using
Electromagnetic fields were first expressed mathematically in theory by Maxwell in 1864. Actually, it was he who revealed the indivisibility of magnetic and electric fields. One of the consequences of the theory was the fact that any disturbance (change) of the electromagnetic field causes the appearance of electromagnetic waves propagating in a vacuum. Calculations have shown 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 Faraday's work (in 1831) on research in a conductor moving or located in a periodically changing magnetic field. Even earlier, in 1819, H. Oersted noticed that if a compass is placed next to a current-carrying conductor, its needle deviates from the natural one, which suggested a direct connection between magnetic and electric fields.
All this indicates that any electrical device is a generator of electromagnetic waves. This property 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 propagates not only in conductive materials, but also in dielectrics (for example, vacuum), a person is constantly in the zone of their action.
If earlier, when there was only “Ilyich’s lamp” in the room, the question did not bother anyone. Now everything is different: the electromagnetic field is measured using special devices to measure 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 (permissible norm). At enterprises and in large companies EMF PDN checks are carried out periodically. It is worth noting that there are still no final results of studies on the effects of EMF on living organisms. Therefore, for example, when working with computer technology 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 from the outlet.
Obviously, few people will decide to completely abandon the use of electrical equipment. However, you can further protect yourself by connecting home appliances to a grounded network, which allows the potential not to accumulate on the housing, but to “drain” into the ground loop. Various extension cords, especially those wound in rings, enhance EMF due to mutual induction. And, of course, you should avoid placing several switched on devices close together.