How the electromagnetic field occurs. Electromagnetic field
Electromagnetic field - this is generating variables electrical and magnetic fields.
The theory of the electromagnetic field was created by James Maxwell in 1865
He theoretically proved that:
Any change over time of the magnetic field leads to the emergence of a changing electric fieldAnd any change with the time of the electric field generates a changing magnetic field.
If the electrical charges move with acceleration, the electrical field created by them periodically changes and itself creates an alternating magnetic field in space, etc.
Sources of the electromagnetic field can be:
- moving magnet;
- electric charge moving with acceleration or fluctuating (in contrast to the charge of moving at a constant speed, for example, in the case of direct current In the conductor, a constant magnetic field is created here.
Electric field There is always around an electric charge, in any reference system, magnetic - in the one relative to which the electric charges are moving.
The electromagnetic field exists in the reference system relative to which the electrical charges move with acceleration.
Try to decide
A piece of amber treated the fabric, and he charged with static electricity. What field can be detected around a fixed amber? Around moving?
The charged body rests relative to the surface of the Earth. The car is evenly and straightforwardly moving relative to the surface of the Earth. Is it possible to detect a constant magnetic field in the reference system associated with the car?
Which field occurs around the electron if he: rests; moving at a constant speed; Moves with acceleration?
The kinescope creates a flow of uniformly moving electrons. Is it possible to detect a magnetic field in the reference system associated with one of the moving electrons?
ELECTROMAGNETIC WAVES
Electromagnetic wheels are an electromagnetic field spreading in space with a finite rate depending on the properties of the medium
Properties of electromagnetic waves:
- express not only in the substance, but also in vacuo;
- spread in vacuo at the speed of light (C \u003d 300,000 km / c);
- these are transverse waves;
- This is a running wave (tolerate energy).
The source of electromagnetic waves are accelerated moving electrical charges.
Electric charge fluctuations are accompanied by electromagnetic radiation having a frequency equal to the frequency of vibrations of charges.
Scale of electromagnetic waves
All the space around us is permeated with electromagnetic radiation. The sun surrounding our bodies, transmitter antennas emit electromagnetic waves, which, depending on their oscillation frequency, wear different names.
Radio waves are electromagnetic waves (C of a wavelength from more than 10000m to 0.005m), which serve to transmit signals (information) to a distance without wires.
In radio communication, radio waves are created by high-frequency currents flowing in an antenna.
Radio waves of various lengths are distributed in different ways.
Electromagnetic radiation with a wavelength smaller than 0.005m, but more than 770 nm, i.e. lying between the radio wave range and the range of visible light are called infrared radiation (IR).
Infrared radiation emit any heated bodies. Furnaces, water heating batteries, electric incandescent bulbs serve as sources of infrared radiation. With the help of special devices, infrared radiation can be converted to visible light and get images of heated items in complete darkness. Infrared radiation is used for drying painted products, walls of buildings, wood.
The visible light includes radiation from a long wave from about 770 nm to 380nm, from red to violet light. The meanings of this section of the spectrum of electromagnetic radiation in a person's life are exceptionally large, since almost all of the information about the world around the world is obtained by vision. Light is a prerequisite for the development of green plants and, therefore, prerequisite For the existence of life Earth.
An invisible eye electromagnetic radiation with a long wave is less than that of purple light, is called ultraviolet radiation (UV). Ultraviolet radiation can be killed by white-and-made bacteria, so medicine is widely used. Ultraviolet radiation in the composition of sunlight causes biological processes, leading to a darkening of human skin - tanning. Drainage lamps are used as sources of ultraviolet radiation in medicine. Tubes of such lamps are made of quartz transparent for ultraviolet rays; Therefore, these lamps are called quartz lamps.
X-rays (RI) are invisible to Az. They pass without substantial absorption through significant layers of substance, opaque for visible light. X-rays are found by their ability to cause a certain glow of some crystals and act on the film. The ability of X-rays to penetrate the thick layers of substances is used to diagnose diseases of the internal organs of a person.
Details Category: Electricity and Magnetism Published 05.06.2015 20:46 Views: 11962The electrical and magnetic field variables under certain conditions can generate each other. They form an electromagnetic field, which is not at all their set. This is a single integer in which these two fields cannot exist without each other.
From the history
The experience of the Danish scientist Hans Christian Ersteda, spent in 1821, showed that electricity generates a magnetic field. In turn, the changing magnetic field can generate an electric current. This proved the English physicist Michael Faraday, opened in 1831 the phenomenon of electromagnetic induction. He is the author of the term "electromagnetic field".
In those days, Newton's long-rise concept was adopted in physics. It was believed that all the bodies act on each other through the emptiness with an infinitely high speed (almost instantly) and at any distance. It was assumed that electrical charges interact in a similar way. Faradays also believed that there are no voids in nature, and the interaction occurs at a final rate through a certain material environment. This medium for electrical charges is electromagnetic field. And it applies at a speed equal to the speed of light.
Theory Maxwell
Combining the results of previous studies, english physicist James Clerk Maxwell In 1864 created theory of electromagnetic field. According to it, the changing magnetic field generates a changing electric field, and the variable electric field generates an alternating magnetic field. Of course, at first one of the fields is created by the source of charges or currents. But in the future these fields can already exist independently of such sources, causing each other's appearance. I.e, electric and magnetic fields are components of a single electromagnetic field.. And any change in one of them causes the appearance of another. This hypothesis is the basis of the Maxwell theory. The electric field generated by the magnetic field is vortex. His power lines are closed.
This theory is phenomenological. This means that it is based on assumptions and observations, and does not consider the cause that causes the occurrence of electrical and magnetic fields.
Properties of electromagnetic field
The electromagnetic field is a combination of electric and magnetic fields, so at each point of its space it is described by two main values: electric field tension E. and magnetic field induction IN .
Since the electromagnetic field is the process of turning the electric field into magnetic, and then the magnetic into electric, then its condition is constantly changing. Spreading 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-ray and gamma radiation.
The voltage and induction vectors of the electromagnetic field are mutually perpendicular, and the plane in which they lie are perpendicular to the direction of propagation of the wave.
In a long-range theory, the speed of propagation of electromagnetic waves was considered an endless large. However, Maxwell proved that it is not. In the substance, electromagnetic waves propagate with a final velocity, which depends on the dielectric and magnetic permeability of the substance. Therefore, Maxwell's theory is called the theory of closestream.
An experimentally theory of Maxwell confirmed the German physicist Heinrich Rudolf Hertz in 1888. He proved that electromagnetic waves exist. Moreover, it measured the speed of propagation of electromagnetic waves in a vacuum, which turned out to be equal to the speed of light.
In integrated form, this law looks like this:
Gauss law for magnetic field
The flow of magnetic induction through a closed surface is zero.
The physical meaning of this law is that there are no magnetic charges in nature. It is impossible to divide the magnets of the magnet. The power lines of the magnetic field are closed.
Faraday induction law
The change in magnetic induction causes the appearance of a vortex electric field.
,
Magnetic field circulation theorem
This theorem describes the sources of magnetic pouls, as well as the fields themselves created by them.
Electric current and change of electrical induction generate a vortex magnetic field.
,
,
E. - electric field strength;
N. - the tension of the magnetic field;
IN - magnetic induction. This vector magnitude showing how power the magnetic field acts on the charge Q value moving at a speed V;
D. - Electrical induction, or electrical displacement. It is a vector value equal to the sum of the voltage vector and polarization vector. Polarization is caused by the displacement of electrical charges under the action of an external electric field relative to their position when there is no such field.
Δ - Operator recruit. The action of this operator on a specific field is called the rotor of this field.
Δ x E \u003d Rot E
ρ - density of third-party electric charge;
j. - current density - the value showing the strength of the current flowing through the area of \u200b\u200bthe area;
from - The speed of light in vacuum.
The study of the electromagnetic field is engaged in science, called electrodynamics. She considers his interaction with bodies having an electric charge. This interaction is called electromagnetic. Classical electrodynamics describes only the continuous properties of the electromagnetic field using the Maxwell equations. Modern quantum electrodynamics believes that the electromagnetic field also has discrete (interrupted) properties. And such electromagnetic interaction occurs with the help of indivisible particles-quanta, not having masses and charge. Kvant electromagnetic field called photon .
Electromagnetic field around us
The electromagnetic field is formed around any conductor with alternating current. Sources of electromagnetic fields are power lines, electric motors, transformers, urban electric transport, railway transport, electric and electronic household appliances - televisions, computers, refrigerators, irons, vacuum cleaners, radio telephones, mobile phones, electric shavers - in short, everything related to consumption or Electricity transmission. Powerful sources of electromagnetic fields - television transmitters, cellular telephone antennas, radar stations, microwave ovens, etc. And since such devices around us are quite a lot, then electromagnetic fields surround us everywhere. These fields affect environment and man. It is impossible to say that this effect is always negative. Electric and magnetic fields existed around a person for a long time, but the power of their radiation has been hundreds of times below the current one for several decades.
Until a certain level, electromagnetic radiation can be safe for humans. So, in medicine with the help of electromagnetic radiation of low intensity healing tissue, eliminate inflammatory processeshave an analgesic effect. UHF devices remove the spasms of the smooth muscles of the intestine and the stomach, improve the metabolic processes in the cells of the body, reducing the tone of the capillaries, reduce blood pressure.
But strong electromagnetic fields cause malfunction of cardiovascular, immune, endocrine and human nervous systems, can cause insomnia, headaches, stress. The danger is that their impact is almost imperceptibly for a person, and violations arise gradually.
How to protect yourself from the environment around us? It is impossible to do this completely, so you need to try to minimize its impact. First you need to position appliances So that they are away from those places where we are most often. For example, you do not need to 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 included in the outlet. But the electromagnetic field disappears only when the device turns off from the electrical network.
Influence on human health and natural electromagnetic fields - cosmic radiation, magnetic field of the Earth.
What is an electromagnetic field, as it affects human health and why measure it - you will learn from this article. Continuing to acquaint you with the assortment of our store, we will tell about the useful devices - indicators of the electromagnetic field (EMF). They can be used both in enterprises and in everyday life.
What is an electromagnetic field?
The modern world is unthinkable without household appliances, mobile phones, electricity, trams and trolley buses, televisions and computers. We are accustomed to them and absolutely not thinking about the fact that any electrical device creates an electromagnetic field around itself. It is invisible, but affects any living organisms, including a person.
The electromagnetic field is a special form of matter that occurs when the interaction of moving particles with electrical charges. The electrical and magnetic field are interconnected with each other and can generate one other - that is why, as a rule, they speak together as a single, electromagnetic field.
The main sources of electromagnetic fields include:
- power lines;
- transformer substations;
- wiring, telecommunications, television and internet cables;
- Ties of cellular communication, radio and broadcasters, amplifiers, cellular antennas and satellite phones, Wi-Fi Routers;
- computers, televisions, displays;
- household electrical appliances;
- induction and microwave (microwave) furnaces;
- electric transport;
- Radars.
Effect of electromagnetic fields on human health
Electromagnetic fields affect any biological organisms - on plants, insects, animals, people. Scientists studying the effect of EMF per person came to the conclusion that the long-term and regular effect of electromagnetic fields can lead to:
- increased fatigue, sleep disorders, headaches, pressure reduction, reduction of the pulse rate;
- disorders in immune, nervous, endocrine, sex, hormonal, cardiovascular systems;
- development of oncological diseases;
- Development of diseases of the Central nervous system;
- Allergic reactions.
Protection against EMF.
Exist sanitary normsestablishing the maximum allowable levels of electromagnetic field strength depending on the time of stay in the danger zone - for residential premises, jobs, places near the sources of a strong field. If there is no possibility to reduce the radiation structurally, for example, from the line of electromagnetic gear (EMF) or cellular tower, then official instructions are being developed, protective equipment for working personnel, sanitary quarantine areas of limited access.
Different instructions regulate the time of the person's stay in the danger zone. Screening grids, films, glazing, suits made of metallized tissue based on polymer fibers are able to reduce the intensity of electromagnetic radiation thousands of times. At the request of the GOST, the EMF radiation zone is protected and are supplied with warning signs "Not to enter, dangerous!" and sign danger electromagnetic field.
Special services with devices constantly monitor the level of EMF tension at workplaces and in residential areas. You can independently take care of your health by buying portable device "Impulse" or pulse Kit + SOEKS Nitrate Tester.
Why do we need household instruments for measuring the electromagnetic field strength?
The electromagnetic field negatively affects human health, so it is useful to know which places where you are (at home, in the office, on panstoneIn the garage) may be dangerous. You should understand that an increased electromagnetic background can create not only your electrical devices, phone numbers, televisions and computers, but also faulty wiring, electrical appliances of neighbors, industrial facilities located nearby.
Experts found out that the short-term impact of the EMF per person is almost harmlessly, but long-term foundation in the zone with an increased electromagnetic background is dangerous. These are such zones and can be detected using a "impulse" type instruments. So, you can check the places where you spend the most time; Children's and her bedroom; study. The device is listed, set regulatory documentsSo you can immediately estimate the degree of danger to you and your loved ones. It is possible that after the examination you decide to push the computer from the bed, get rid of cell phone With an enhanced antenna, change the old microwave oven to a new one, replace the insulation of the refrigerator door with the No Frost mode.
Electricity around us
Electromagnetic field (definition from BSE) - This is a special form of matter by 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 of a particle can receive a charge. As in history with chicken and egg. The point is that the charged particles and the electromagnetic field are inseparable from each other and can not exist without each other. Therefore, the definition does not give us the opportunity to understand the essence of the phenomenon of the electromagnetic field and the only thing that should be remembered that it is special form of matter! The theory of the electromagnetic field was developed by James Maxwell in 1865
What is an electromagnetic field? It can be imagined that we live in the electromagnetic universe, which is entirely completely permeated with 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 electoral. Accordingly, electromagnetic fields can be divided into two types: static, that is, emitted by charged bodies (particles) and inherent from them, and dynamic, distributed in space, being torn off from the source radiant. The dynamic electromagnetic field in physics is represented as two mutually perpendicular waves: electrical (E) and magnetic (H).
The fact that the electric field is generated by variable magnetic field, and magnetic The field is an electrical variable, leads to the fact that the electric and magnetic field variables do not exist separately from each other. The electromagnetic field of fixed or evenly moving charged particles is directly related to the particles themselves. With the accelerated movement of these charged particles, the electromagnetic field "breaks" from them and exists independently in the form of electromagnetic waves, not 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:
Magnetic field of land. The magnitude of the geomagnetic field of the Earth varies on the earth's surface from 35 mkl at the equator to 65 mkl near the poles.
Electrical field of landit is directed normally to the earth's surface, charged negatively relatively upper layers Atmosphere. The voltage of the electric field at the surface of the Earth is 120 ... 130 V / m and decreases with a height of approximately exponentially. Annual changes of EP are similar in nature throughout the land: the maximum voltage of 150 ... 250 V / m in January-February and the minimum 100 ... 120 V / m in June-July.
Atmospheric electricity - These are electrical phenomena in the earth's atmosphere. There are always positive and negative electrical charges in the air (reference) - ions arising under the action of radioactive substances, cosmic rays and ultraviolet radiation of the Sun. Earth Charged negatively; Between it and the atmosphere there is a big difference in potentials. The voltage of the electrostatic field increases sharply during the thunderstorms. The frequency range of atmospheric discharges lies between 100 Hz and 30 MHz.
Extraterrestrial sourcesinclude radiation outside the land atmosphere.
Biological electromagnetic background. Biological objects, like others physical bodiesAt temperatures above the absolute zero, EMF radiates 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 EMP with a frequency of 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 emissions (0 - 3 kHz)
This group includes all production systems, 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 for 18-32% of the territory of cities is formed as a result of automotive movement. Electromagnetic wavesarising from the movement of transport, create interference with television and radio and can also provide harmful effects on the human body.
Sources of high-frequency emissions (from 3 kHz to 300 GHz)
This group includes functional transmitters - sources of an electromagnetic field for transmitting or receiving information. These are commercial transmitters (radio, television), radio telephones (auto-, radiotelephones, radio units, amateur radio transmitters, production radiotelephones), directional radio communication (satellite radio communications, ground relay stations), navigation (air traffic, shipping, radio), locators (air Message, shipping, transport locators, air transport control). Here also applies different technological equipmentusing microwave radiation, variables (50 Hz - 1 MHz) and pulse fields, household equipment (Microwave ovens), means of visual display of information on electronic radial tubes (PC monitors, TVs, etc.). For scientific research In medicine, ultra-high frequency currents are used. Electromagnetic fields arising from such currents are certain professional harm, so it is necessary to take measures to protect against their impact on the body.
The main technogenic 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).
