Electromagnetic waves. Electromagnetic field

Electromagnetic field

The electromagnetic field refers to this type of matter that occurs around moving charges. It consists of electric, as well as magnetic fields. Their existence is interconnected, as they can not be separate and independently of each other, because, one field creates another.

Now let's try to approach the topic electronic magnetic field in details. From the definition, it can be concluded that in the event of a change in the electric field, the prerequisites for the occurrence of the magnetic field appear. And since the electric field has a property with time to change and cannot be called unchanged, the magnetic field is also variable.

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

And even if the current will turn off in the conductor, the electromagnetic field will not disappear anyway, but will continue to exist and distribute in space.

Properties of electromagnetic waves

Maxwell theory. Vortex electric field

James Clerk Maxwell, a famous British physicist in 1857, a work was written in 1857, in which he led evidence that the fields such as electrical and magnetic are closely related to each other.

According to his theory, it was necessary that the variable magnetic field had a property to create such a new EP, which differs from the previous electric field created using the current source, since this new electric field is vortex.

And here we see that the vortex electric field is a field that the power lines are closed. That is, it should be noted that the electric field has the same closed lines as the magnetic field.

From this it follows that the alternating magnetic field can create a vortex electric field, and the vortex electric field has the ability to make the charges move. And in the end we get an induction electric current. Maxwell follows that fields such as electric and magnetic closely exist with each other.

That is, a moving electric charge is needed for the existence of a magnetic field. Well, the electric field is created thanks to the resting electrical charge. This is such a transparent relationship exists between the fields. From this we can make another conclusion that various types of fields can be observed in different reference systems.

If you follow Maxwell's theory, then we can sum up that the variables electrical and magnetic fields are not able to exist separately, because with a change, the magnetic field generates an electric field, and the changing electric field generates magnetic.

Natural sources of electromagnetic fields

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

Natural sources of EMF include:

First, it is a constant electric and magnetic polo of the Earth.
Secondly, such sources include radio waves, transforming such space sources as the sun, stars, etc.
Thirdly, these sources are atmospheric processes as lightning discharges, etc.

Anthropogenic (artificial) sources of electromagnetic fields

In addition to natural sources of EMF, they still arise and thanks to anthropogenic sources. Such sources include X-rays that are used in medical institutions. They are used to transmit information using various radio stations, mobile stations and also TV antennas. Yes, and electricity that is in every rosette also forms EMF, but truth, lower frequency.

Effect of EMF on human health

Modern society is currently not thinking of his life, without such benefits of civilization as the presence of various household appliances, computers, mobile communications. Of course, they facilitate our lives, but create electromagnetic fields around us. Naturally, we can not see EMF with you, but they surround us everywhere. They are present in our homes, at work and even in transport.

We can safely say that a modern person lives in a solid electromagnetic field, which, unfortunately, has a huge effect on human health. With a long-term effect of the electromagnetic field on the human body, such unpleasant symptoms appear as chronic fatigue, irritability, sleep disruption, attention and memory. Such prolonged effects of EMF can cause human headache, infertility, violations in the work of nervous and cardiac systems, as well as the emergence of oncological diseases.

Electromagnetic field, a special form of matter. Through the electromagnetic field, interaction between charged particles is carried out.

The behavior of the electromagnetic field is studied by classical electrodynamics. The electromagnetic field is described by Maxwell equations that bind the values \u200b\u200bcharacterizing the field with its sources, that is, with charges and currents distributed in space. The electromagnetic field of fixed or uniformly moving charged particles is inextricably linked with these particles; With an accelerated movement of the particles, the electromagnetic field "breaks" from them and exists independently in the form of electromagnetic waves.

From the Maxwell equations it follows that the alternating electric field generates a magnetic, and the alternating magnetic field generates electric, so the electromagnetic field can exist in the absence of charges. The generation of the electromagnetic field by the alternating magnetic field and the magnetic field by the electrical variables leads to the fact that the electrical and magnetic fields do not exist separately, independently of each other. Therefore, the electromagnetic field is the form of matter, determined at all points with two vector magnitudes, which characterize the two components - "electric field" and "magnetic field", and has a power effect on charged particles, depending on their speed and the amount of their charge.

The electromagnetic field in vacuo, that is, in a free state, not associated with particles of the substance, exists in the form of electromagnetic waves, and is distributed in emptiness in the absence of very strong gravitational fields at speeds, equal speed Sveta c. \u003d 2, 998. 10 8 m / s. This field is characterized by electric field strength. E. and magnetic field induction IN. To describe the electromagnetic field, electrical induction is also used in the medium. D. and magnetic field tension N.. In substance, as well as in the presence of very strong gravitational fields, it is near the very large mass of the substance, the speed of propagation of the electromagnetic field is less than the magnitude c..

The components of vectors characterizing the electromagnetic field form, according to the theory of relativity, one physical quantity - the tensor of the electromagnetic field, the components of which are converted to the transition from one inertial reference system to the other in accordance with the Lorentz transforms.

The electromagnetic field has energy and pulse. The existence of the pulse of the electromagnetic field was first discovered experimentally in the experiments of P. N. Lebedev to measure the pressure of light in 1899. The electromagnetic field always has energy. Electromagnetic field energy density \u003d 1/2 (ED + VN).

The electromagnetic field is distributed in space. The density of the power of the electromagnetic field is determined by the Pinging vector S \u003d., Unit of measurement W / m 2. Pinging vector direction perpendicular E. and H. and coincides with the direction of propagation of electromagnetic energy. Its value is equal to the energy transferred through a single platform perpendicular S. per unit time. Pulse density field in vacuum K \u003d S / C 2 \u003d / C 2.

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

The electromagnetic field is the variables of electrical and magnetic fields generating each other.
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 occurrence of a changing electric field, and any change with the electric field time 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 oscillating (in contrast to the charge moving at a constant speed, for example, in the case of direct current in the conductor, a constant magnetic field is created here).

The electric field always exists around the electric charge, in any reference system, magnetic - in the one relative to which the electric charges move.
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. The light is a prerequisite for the development of green plants and, consequently, a prerequisite for the existence of life of the 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 sunlight Causes biological processes leading to 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.

The electromagnetic field is such a type of matter that occurs around moving charges. For example, around the conductor with a current. The electromagnetic field consists of two components of this electric and magnetic field. Regardless of each other, they cannot exist. One generates another. When changing the electric field, magnetic occurs immediately. Electromagnetic Wave Spread Speed V \u003d C / EM Where e. and m. Accordingly, the magnetic and dielectric permeability of the medium in which the wave is distributed. The electromagnetic wave in the vacuum applies at the speed of light, that is, 300,000 km / s. Since the dielectric and magnetic permeability of the vacuum is considered to be equal to 1. When the electric field changes, a magnetic field occurs. Since the electrical field that caused it is not unchanged (that is, it changes in time) then 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 (it does not matter whether it is an electric or magnetic) source will serve the previous field, and not the original source, that is, a conductor with a current. Thus, even after turning off the current in the conductor, the electromagnetic field will continue to exist and distribute in space. The electromagnetic wave spreads in space in all directions from its source. You can imagine a light bulb, the rays of light from it spread in all directions. The electromagnetic wave in propagation transfers energy in space. The stronger the current in the conductor called the field, the greater the energy tolerant of the wave. Also, energy depends on the frequency of radiated waves, with an increase in it 2.3.4 times the energy of the wave will increase by 4.9.16 times, respectively. That is, the spread energy of the wave is proportional to the square of the frequency. The best conditions for the spread of waves are created when the conductor is long, equal to the wavelength. The power lines of the magnetic and electric flying mutually perpendicularly. Magnetic power lines cover the conductor with current and always closed. Electric power lines go from one charge to another. Electromagnetic wave is always a transverse wave. That is, the power lines both magnetic and electrical lie in the perpendicular plane to the distribution direction. Electromagnetic field strength Power characteristics of the field. Also tension, vector magnitude that is, it has the beginning and direction. Field voltage is aimed at tangent to power lines. Since the voltage of the electric and magnetic field is perpendicular to each other, that is, the rule by which you can determine the direction of propagation of the wave. When rotating the screw along the shortest path from the tension vector of the electric field to the magnetic field voltage vector, the progressive movement of the screw will indicate the direction of the wave propagation.

Magnetic field and its characteristics. When the electric current passes through the conductor around it is formed a magnetic field. A magnetic field represents one of the types of matter. It has an energy that manifests itself in the form of electromagnetic forces acting on separate moving electrical charges (electrons and ions) and their streams, i.e. electric current. Under the influence of electromagnetic forces, moving charged particles are deviated from their initial path in the direction perpendicular to the field (Fig. 34). The magnetic field is formed Only around moving electrical charges, and its action applies, too, only on moving charges. Magnetic and electric fields Inseparable and form together electromagnetic field. Any change electric fieldit leads to the appearance of a magnetic field and, on the contrary, any change in the magnetic field is accompanied by the occurrence of the electric field. Electromagnetic field It spreads at the speed of light, i.e. 300,000 km / s.

Graphic image of a magnetic field. A graphically magnetic field is depicted by magnetic power lines, which are carried out so that the direction of the power line at each point of the field coincides with the direction of the forces of the field; Magnetic power lines are always continuous and closed. The direction of the magnetic field at each point can be determined using a magnetic arrow. The North Pole arrows is always installed in the direction of the field forces. The end of the permanent magnet from which the power lines extends (Fig. 35, a) is considered to be the northern pole, and the opposite end, which includes the power lines - the southern pole (the power lines passing inside the magnet are not shown). The distribution of power lines between the poles of a flat magnet can be detected using steel sawdust, fastened to a sheet of paper, laid on the poles (Fig. 35, b). For a magnetic field in the air gap between two parallel-locatedly located variepete poles of a constant magnet, a uniform distribution of power magnetic lines is characterized (Fig. 36)

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 trolleybuses, 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 and satellite phone antennas, 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, gender, 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 the sign of the danger of the electromagnetic field.

Special services with devices constantly monitor the level of EMF tension at workplaces and in residential areas. You can also take care of your health by purchasing a portable Impulse device or a "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, in the garage, in the garage) may be dangerous. You must understand that an elevated electromagnetic background can create not only your electrical appliances, telephones, 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 contains values \u200b\u200bset by regulatory documents, so that 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 a cell phone with a reinforced antenna, change the old microwave oven to a new one, replace the insulation of the refrigerator door with the No Frost mode.