Electromagnetic fields and radiation surround us everywhere. 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, exactly electrical devices created modern world the way we know it. However, in recent times Increasingly, the question is 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 are known from school course physics are a special Key Feature similar fields is the ability to interact in a certain way with bodies and particles that have an electric charge. As the name implies, electromagnetic fields are a combination of magnetic and electric fields, and in this case they are so closely interconnected that they are considered to be a single entity. 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 magnetic and electric fields. One of the consequences of the theory was the fact that any perturbation (change) of the electrical magnetic field is the cause of the appearance of electromagnetic waves propagating in vacuum with Calculations have shown that light (all parts of the spectrum: infrared, visible, ultraviolet) is precisely an electromagnetic wave. In general, classifying radiation by wavelength, they distinguish between X-ray, radio, etc.
The appearance of Maxwell's theory was preceded by the work of Faraday (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, 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 appliance 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 their zone of action.
If earlier, when there was only “Ilyich’s light bulb” in the room, the question did not bother anyone. Things are different now: measurement electromagnetic field performed using special devices to measure the field strength. Both EMF components are fixed in certain range frequencies (depending on the sensitivity of the device). The SanPiN document indicates PDN ( allowable rate). At enterprises and large companies, EMF PDN checks are periodically performed. It should be noted 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. The equipment is completely safe when the power cord is unplugged from the socket.
Obviously, few people will dare to completely abandon the use of electrical equipment. However, you can additionally protect yourself by connecting home 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 coiled ones, amplify EMF by mutual induction. And, of course, the close placement of several turned-on devices at once should be avoided.
electricity around us
Electromagnetic field (definition from TSB)- This special form 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. Perhaps only due to the presence of an electromagnetic field, particles can receive a charge. Just like the chicken and egg story. The bottom line is that charged particles and the 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 to remember is that this special form of matter! The electromagnetic field theory was developed by James Maxwell in 1865.
What is an electromagnetic field? One can imagine that we live in the electromagnetic Universe, which is completely permeated by the 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, electromagnetic fields can be divided into two types: static, that is, emitted by charged bodies (particles) and integral to them, and dynamic, propagating in space, being torn off from the source that radiated it. A dynamic electromagnetic field in physics is represented as two mutually perpendicular waves: electric (E) and magnetic (H).
The fact that an electric field is generated by an alternating magnetic field, and 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. At fast motion these charged particles, the electromagnetic field "breaks away" from them and exists independently in the form of 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. Value geomagnetic field The earth is changing by earth's surface from 35 µT at the equator to 65 µT near the poles.
Earth's electric field directed normally to the earth's surface, negatively charged relative to the upper layers of the atmosphere. The electric field strength near the Earth's surface is 120…130 V/m and decreases approximately exponentially with height. Annual changes in EP are similar in nature throughout the Earth: the maximum intensity is 150...250 V/m in January-February and the minimum is 100...120 V/m in June-July.
atmospheric electricity- This electrical phenomena in 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 Sun. Earth negatively charged; there is a large potential difference between it and the atmosphere. The strength of the electrostatic field increases sharply during thunderstorms. The frequency range of atmospheric discharges lies 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 emit EMF in the range of 10 kHz - 100 GHz. This is explained chaotic movement 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 watts. Human body also emits EMF 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:
Sources of low-frequency radiation (0 - 3 kHz)
This group includes all systems for the production, transmission and distribution of electricity (power lines, transformer substations, power stations, various cable systems), home and office electrical and electronic equipment, including PC monitors, electric vehicles, 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 car traffic. Electromagnetic waves generated during the movement of vehicles interfere with television and radio reception, and can also have harmful effect on the human body.
RF 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), radio telephones (car, radio telephones, CB radio, amateur radio transmitters, industrial radio telephones), directional radio communications (satellite radio communications, ground relay stations), navigation (air traffic, shipping, radio point), locators (air communication, shipping, traffic locators, air traffic control). This also includes various technological equipment using microwave radiation, alternating (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 measures to protect against their effects on the body.
The main technogenic sources are:
A feature of exposure 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).
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 over time in the magnetic field results in a changing electric field, and any change over time in the electric field 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 (as opposed to a charge moving with constant speed, for example, in the case direct current in the 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 with final 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 various lengths are distributed 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 range visible light, are called infrared radiation (IR).
Infrared radiation emit any heated body. Sources of infrared radiation are stoves, water heaters, electric lamps incandescent. 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 prerequisite for the development of green plants and, therefore, 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 is capable of killing pathogenic bacteria, so it is widely used in medicine. UV radiation included sunlight causes biological processes leading 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, 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 thick layers of substances is used to diagnose diseases. internal organs person.
Electromagnetic field
The electromagnetic field refers to the kind 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.
And now let's try to approach the topic of the electromagnetic field in more detail. From the definition, we can conclude that in the case of a change in the electric field, prerequisites for the emergence of a magnetic field appear. And since the electric field tends to change over time and cannot be called constant, the magnetic field is also variable.
When one field changes, another is generated. And no matter what the next field will be, the source will be the previous field, that is, the conductor with current, and not its original source.
And even in the case when the current is turned off in the conductor, the electromagnetic field will still not disappear anywhere, but will continue to exist and spread in space.
Properties of electromagnetic waves
Maxwell's theory. Vortex electric field
James Clerk Maxwell, famous British physicist in 1857, a work was written 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 tends to create such a new electric field, which differs from the previous electric field created using a current source, since this new electric field is vortex.
And here we see that the vortex electric field is such a field for which lines of force are closed. That is, it should be noted that the lines of the electric field are as closed as those of the magnetic field.
From this follows the conclusion 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 the induction electricity. It follows from Maxwell's work that such fields as electric and magnetic closely exist with each other.
That is, a moving electric charge is necessary for the existence of a magnetic field. Well, the electric field is created due to the resting electric charge. Here such transparent interrelation exists between fields. From this we can draw another conclusion, that in different systems readings can be observed different kinds fields.
If we follow Maxwell's theory, then we can conclude that alternating electric and magnetic fields are not able to exist separately, because when a 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 electromagnetic fields, although they remain invisible to our eyes, 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 such atmospheric processes as lightning discharges, etc.
Anthropogenic (artificial) sources of electromagnetic fields
Except natural sources appearance of EMF, they also arise due to anthropogenic sources. Such sources include X-rays, which are used in medical institutions. They are also used to transmit information using various radio stations, mobile communication stations and also TV antennas. Yes, and the electricity that is in every outlet also forms an EMF, but it is true, at a lower frequency.
The impact of EMF on human health
Modern society currently cannot imagine its life without such benefits of civilization as the presence of various household appliances, computers, mobile communications. They, of course, make our lives easier, but they create electromagnetic fields around us. Naturally, you and I cannot see EMF, but they surround us everywhere. They are present in our homes, at work and even in transport.
It is safe to say that modern man lives in a continuous electromagnetic field, which, unfortunately, has a huge impact on human health. With prolonged influence of the electromagnetic field on the human body, there are such unpleasant symptoms, as chronic fatigue, irritability, sleep disturbance, attention and memory. Such prolonged exposure to EMF can cause headaches, infertility, disorders in the functioning of the nervous and cardiac systems, as well as the appearance of oncological diseases in a person.
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. electromagnetic wave In a vacuum, it propagates 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. The electromagnetic wave is always 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, the tension 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)
