An electric charge placed at a certain point in space changes the properties of this space. That is, the charge generates an electric field around itself. An electrostatic field is a special kind of matter.
The electrostatic field does not change over time.
The strength characteristic of the electric field is the intensity
The strength of the electric field at a given point is a vector physical quantity that is numerically equal to the force acting on a unit positive charge placed at a given point of the field.
If the test charge is acted upon by forces from several charges, then these forces are independent according to the principle of superposition of forces, and the resultant of these forces is equal to the vector sum of forces. The principle of superposition (superposition) of electric fields: The electric field strength of the system of charges at a given point in space is equal to the vector sum of the strengths of the electric fields created at a given point in space by each charge of the system separately:or
It is convenient to represent an electric field graphically using lines of force.
Lines of force (lines of electric field strength) are called lines whose tangents at each point of the field coincide with the direction of the strength vector at a given point.
Lines of force start at positive charge and end at negative (Power lines of electrostatic fields of point charges.).
The density of the lines of tension characterizes the field strength (the denser the lines are, the stronger the field).
The electrostatic field of a point charge is inhomogeneous (closer to the charge, the field is stronger).Lines of force of electrostatic fields of infinite uniformly charged planes.
The electrostatic field of infinite uniformly charged planes is homogeneous. An electric field, the strength at all points of which is the same, is called uniform.
Power lines of electrostatic fields of two point charges.
Potential is an energy characteristic of an electric field.
Potential- a scalar physical quantity equal to the ratio of the potential energy possessed by an electric charge at a given point of the electric field to the value of this charge.The potential shows what potential energy a unit positive charge, placed at a given point of the electric field, will have. φ = W / q
where φ is the potential at a given point in the field, W is the potential energy of the charge at a given point in the field.
The unit of measurement of potential in the SI system is taken [φ] = B(1V = 1J / C)
The potential at a point is taken as a unit of potential, for moving to which from infinity of an electric charge of 1 C, it is required to perform work equal to 1 J.
Considering the electric field created by the system of charges, one should use to determine the field potential superposition principle:
The potential of the electric field of the system of charges at a given point in space is equal to the algebraic sum of the potentials of the electric fields created at a given point in space by each charge of the system separately:
An imaginary surface, at all points of which the potential takes the same values, is called equipotential surface. When an electric charge moves from point to point along the equipotential surface, its energy does not change. An infinite set of equipotential surfaces for a given electrostatic field can be constructed.
The intensity vector at each point of the field is always perpendicular to the equipotential surface drawn through this point of the field.
An electric field is a vector field that acts around particles with an electric charge. It is part of the electromagnetic field. It is characterized by the absence of real visualization. It is invisible, and can be seen only as a result of forceful action, to which other charged bodies with opposite poles react.
How an electric field works and works
In fact, the field is a special state of matter. Its action is manifested in the acceleration of bodies or particles that have an electric charge. Its characteristic features include:
- Action only in the presence of an electric charge.
- Lack of boundaries.
- The presence of a certain amount of impact.
- The ability to determine only by the result of the action.
The field is inextricably linked with the charges that are in a particular particle or body. It can form in two cases. The first provides for its appearance around electric charges, and the second when electromagnetic waves move, when the electromagnetic field changes.
Electric fields act on electrically charged particles stationary relative to the observer. As a result, they receive a forceful influence. An example of the impact of the field can be observed in everyday life. To do this, it is enough to create an electric charge. Physics textbooks offer the simplest example for this, when a dielectric is rubbed against a woolen product. It is quite possible to get the field by taking a plastic ballpoint pen and rubbing it on your hair. A charge is formed on its surface, which leads to the appearance of an electric field. As a result, the handle attracts small particles. If it is presented to finely torn pieces of paper, they will be attracted to it. The same result can be achieved with a plastic comb.
A common example of the manifestation of an electric field is the formation of small light flashes when removing clothes made of synthetic materials. As a result of being on the body, dielectric fibers accumulate charges around them. When such a piece of clothing is removed, the electric field is subjected to various impact forces, which leads to the formation of light flashes. This is especially true for winter clothing, in particular sweaters and scarves.
Field properties
3 indicators are used to characterize the electric field:
- Potential.
- Tension.
- Voltage.
Potential
This property is one of the main ones. Potential indicates the amount of stored energy used to move charges. As they shift, energy is wasted, gradually approaching zero. An ordinary steel spring can be a visual analogy for this principle. In a calm position, it has no potential, but only until it is compressed. From such an impact, it receives the energy of counteraction, therefore, after the cessation of the influence, it will definitely be straightened. When the spring is released, it instantly straightens. If there are objects in her path, she will begin to move them. Returning directly to the electric field, the potential can be compared to the applied forces to straighten back.
The electric field has potential energy, which makes it capable of performing a certain action. But moving a charge in space, it depletes its resource. In the same case, if the movement of the charge inside the field is carried out under the influence of an external force, then the field not only does not lose its potential, but also replenishes it.
Also, for a better understanding of this value, one more example can be given. Suppose that an insignificant positively charged charge is located far beyond the range of the electric field. This makes him completely neutral and excludes mutual contact. If, as a result of the action of any external force, the charge moves towards the electric field, then upon reaching its boundary, it will be drawn into a new trajectory. The energy of the field spent on the influence relative to the charge at a certain point of influence, and will be called the potential at this point.
The expression of the electric potential is carried out through the unit of measurement Volts.
Tension
This measure is used to quantify a field. This value is calculated as the ratio of the positive charge affecting the force of the action. In simple language, tension expresses the strength of the e-field in a specific place and time. The higher the intensity, the more pronounced the effect of the field on surrounding objects or living beings will be.
Voltage
This parameter is derived from potential. It is used to demonstrate the quantitative relationship of the action that the field produces. That is, the potential itself shows the amount of accumulated energy, and the voltage shows the losses to ensure the movement of charges.
In an electric field, positive charges move from points of high potential to places where it is lower. As for negative charges, they move in the opposite direction. As a consequence, work is carried out using the potential energy of the field. In fact, the voltage between the points qualitatively expresses the work done by the field to transfer a unit of oppositely charged charges. Thus, the terms voltage and potential difference are one and the same.
Visual display of the field
The electric field has a conventional visual expression. For this, graphic lines are used. They coincide with the lines of force action that radiate charges around them. In addition to the line of action of the forces, their direction is also important. For the classification of lines, it is customary to use a positive charge as the basis for determining directions. Thus, the arrow of motion of the field goes from positive particles to negative ones.
Drawings depicting e-fields have an arrow-like direction on the lines. Schematically, they always have a conventional beginning and an end. Thus, they do not lock on to themselves. Lines of force originate at the point where the positive charge is located and end at the place of negative particles.
The electric field can have different types of lines, depending not only on the polarity of the charge, which contributes to their formation, but also on the presence of external factors. So, when opposite fields meet, they begin to act attractively on each other. Distorted lines take on the shape of bent arcs. In the same case, when 2 identical fields meet, they are repelled in opposite directions.
Scope of application
The electric field has a number of properties that have found useful applications. This phenomenon is used to create various equipment for work in several very important areas.
Medical use
Exposure to an electric field on certain parts of the human body makes it possible to increase its actual temperature. This property has found its application in medicine. Specialized devices provide exposure to the necessary areas of damaged or diseased tissues. As a result, their blood circulation is improved and a healing effect arises. The field acts with a high frequency, therefore, a point effect on the temperature gives its results and is quite palpable for the patient.
Application in chemistry
This area of science involves the use of various pure or mixed materials. In this regard, work with e-fields could not bypass this industry. The components of mixtures interact with the electric field in different ways. In chemistry, this property is used to separate liquids. This method has found laboratory application, but it is also found in industry, although less often. For example, when exposed to a field, polluting components are separated in oil.
The electric field is applied for water filtration treatment. It is capable of separating individual groups of pollutants. This method of processing is much cheaper than using replacement cartridges.
Electrical engineering
The use of an electric field has very interesting applications in electrical engineering. So, a source-to-consumer method has been developed. Until recently, all developments were theoretical and experimental. There is already an efficient implementation of the technology of the USB plug-in smartphone. This method does not yet allow the transmission of energy over a long distance, but it is being improved. It is quite possible that in the near future the need for charging cables with power supplies will disappear completely.
When performing electrical installation and repair work, an LED is used, acting on the basis of a circuit. In addition to a number of functions, it can respond to an electric field. Due to this, when the probe approaches the phase wire, the indicator starts to glow without actually touching the conductive core. It reacts to the field emanating from the conductor even through the insulation. The presence of an electric field allows you to find conductive wires in the wall, as well as determine their break points.
You can protect yourself from the effects of the electric field with a metal shield, inside which it will not be. This property is widely used in electronics to eliminate the mutual influence of electrical circuits that are located fairly close to each other.
Potential future applications
There are also more exotic possibilities for the electric field, which science does not yet possess. These are communications faster than the speed of light, teleportation of physical objects, movement in one instant between open locations (wormholes). However, the implementation of such plans will require much more sophisticated research and experiments than conducting experiments with two possible outcomes.
However, science is developing all the time, discovering all the new possibilities of using the electric field. In the future, its scope of use may expand significantly. It is possible that it will find application in all significant areas of our life.
Electrostatic field as well as the electric field is a special form of matter that surrounds bodies that have an electric charge. But unlike the latter, an electrostatic field is created only around stationary charged bodies, that is, when there are no conditions for creating an electric current.
An electrostatic field is characterized by properties that distinguish it from other types of fields generated in electrical circuits.
Its main difference is that its lines of force never intersect or touch each other. If an electrostatic field is created by a positive charge, then its lines of force begin with a charge and end somewhere in infinity. If we are dealing with a negative charge, then the lines of force of its electrostatic field, on the contrary, begin somewhere at infinity, and end at the charge itself. That is, they are directed from a positive charge or to a negative one.
By the way, the larger the charge, the stronger the field it creates and the greater the density of its lines of force. 
True, the field lines are rather a graphic (imaginary) image of it, adopted in physics and electronics. In fact, none of the margins creates clear drawn lines.
The main characteristic by which the electrical and physical properties of the electrostatic field are judged is its strength. It shows with what force the field acts on electric charges.
The entire surrounding space is permeated by electromagnetic fields.
There are natural and man-made sources of electromagnetic fields.
Natural sources of electromagnetic field:
- atmospheric electricity;
- radio emission from the Sun and galaxies (relic radiation uniformly distributed in the Universe);
- electric and magnetic fields of the Earth.
Sources technogenic electromagnetic fields are various transmitting equipment, switches, separating high-frequency filters, antenna systems, industrial installations equipped with high-frequency (HF), ultra-high-frequency (UHF) and microwave (microwave) generators.
Sources of electromagnetic fields in production
The sources of EMF in production include two large groups of sources:
Dangerous effects on workers can be caused by:
- RF EMF (60 kHz - 300 GHz),
- electric and magnetic fields of industrial frequency (50 Hz);
- electrostatic fields.
Sources of radio frequency waves are primarily radio and television broadcasting stations. The classification of radio frequencies is given in table. 1. The effect of radio waves largely depends on the characteristics of their propagation. It is influenced by the nature of the relief and cover of the Earth's surface, large objects and structures located on the way, etc. Woodlands and uneven terrain absorb and scatter radio waves.
Table 1. RF range
Electrostatic fields are created in power plants and during electrical processes. Depending on the sources of formation, they can exist in the form of an actual electrostatic field (the field of stationary charges). In industry, electrostatic fields are widely used for electro-gas cleaning, electrostatic separation of ores and materials, electrostatic application of paints and varnishes and polymer materials. Static electricity is generated during the manufacture, testing, transportation and storage of semiconductor devices and integrated circuits, grinding and polishing of cases for radio and television receivers, in the rooms of computing centers, in duplicating equipment, as well as in a number of other processes where dielectric materials are used. Electrostatic charges and the electrostatic fields created by them can occur when dielectric fluids and some bulk materials move through pipelines, pouring dielectric fluids, rolling film or paper into a roll.
Magnetic fields are created by electromagnets, solenoids, capacitor-type installations, cast and sintered magnets, and other devices.
Sources of electric fields
Any electromagnetic phenomenon, considered as a whole, is characterized by two sides - electrical and magnetic, between which there is a close connection. The electromagnetic field also always has two interconnected sides - the electric field and the magnetic field.
A source of industrial frequency electric fields are current-carrying parts of operating electrical installations (power lines, inductors, capacitors of thermal installations, feeder lines, generators, transformers, electromagnets, solenoids, pulse installations of semi-periodic or capacitor type, cast and sintered magnets, etc.). Long-term exposure to an electric field on the human body can cause disruption of the functional state of the nervous and cardiovascular systems, which is expressed in increased fatigue, decreased quality of work, pain in the heart, changes in blood pressure and pulse.
For an electric field of industrial frequency in accordance with GOST 12.1.002-84, the maximum permissible level of electric field strength, in which it is not allowed to stay in which without the use of special protective equipment during the whole working day, is 5 kV / m. In the interval over 5 kV / m to 20 kV / m inclusive, the permissible residence time T (h) is determined by the formula T = 50 / E - 2, where E is the intensity of the acting field in the controlled area, kV / m. With a field strength above 20 kV / m up to 25 kV / m, the time spent by personnel in the field should not exceed 10 minutes. The maximum permissible value of the electric field strength is set equal to 25 kV / m.
If it is necessary to determine the maximum permissible electric field strength for a given residence time in it, the intensity level in kV / m is calculated using the formula E - 50 / (T + 2), where T is the time spent in the electric field, h.
The main types of collective protection means against the influence of an electric field of industrial frequency currents are shielding devices - an integral part of an electrical installation designed to protect personnel in open switchgears and on overhead power lines (Fig. 1).
The shielding device is necessary when inspecting equipment and during operational switching, monitoring the production of work. Structurally, shielding devices are made in the form of canopies, awnings or partitions made of metal ropes. rods, nets. Shielding devices must be anti-corrosive and grounded.
Rice. 1. Shielding canopy over the passage to the building
To protect against the influence of an electric field of power-frequency currents, shielding suits are also used, which are made of a special fabric with metallized threads.
Sources of electrostatic fields
At enterprises, substances and materials with dielectric properties are widely used and obtained, which contributes to the generation of static electricity charges.
Static electricity is generated by friction (contact or separation) of two dielectrics against each other or dielectrics against metals. At the same time, electric charges can accumulate on the rubbing substances, which easily drain into the ground if the body is a conductor of electricity and it is grounded. On dielectrics, electric charges are held for a long time, as a result of which they are called static electricity.
The process of the emergence and accumulation of electric charges in substances is called electrification.
The phenomenon of static electrification is observed in the following main cases:
- in the stream and when splashing liquids;
- in a stream of gas or steam;
- upon contact and subsequent removal of two solid
- dissimilar bodies (contact electrification).
A discharge of static electricity occurs when the intensity of the electrostatic field above the surface of a dielectric or conductor, due to the accumulation of charges on them, reaches a critical (breakdown) value. For air, the breakdown voltage is 30 kV / cm.
People working in the area affected by the electrostatic field have a variety of disorders: irritability, headache, sleep disturbance, loss of appetite, etc.
The permissible levels of intensity of electrostatic fields are established by GOST 12.1.045-84 “Electrostatic fields. Permissible levels at workplaces and requirements for control "and the Sanitary and Hygienic Standards for Permissible Electrostatic Field Strength (GN 1757-77).
These regulatory legal acts apply to electrostatic fields created during the operation of high voltage direct current electrical installations and electrification of dielectric materials, and establish permissible levels of electrostatic field strength at the workplaces of personnel, as well as general requirements for control and protective equipment.
The permissible levels of the intensity of electrostatic fields are set depending on the time spent at the workplace. The maximum permissible level of intensity of electrostatic fields is 60 kV / m for 1 hour.
When the intensity of electrostatic fields is less than 20 kV / m, the residence time in electrostatic fields is not regulated.
In the voltage range from 20 to 60 kV / m, the permissible time spent by personnel in an electrostatic field without protective equipment depends on the specific voltage level at the workplace.
Measures of protection against static electricity are aimed at preventing the occurrence and accumulation of static electricity charges, creating conditions for the dissipation of charges and eliminating the danger of their harmful effects. Basic protection measures:
- prevention of the accumulation of charges on electrically conductive parts of the equipment, which is achieved by grounding equipment and communications on which charges may appear (devices, tanks, pipelines, conveyors, unloading devices, overpasses, etc.);
- reduction of the electrical resistance of the processed substances;
- the use of static electricity neutralizers that create positive and negative ions near electrified surfaces. Ions carrying a charge opposite to the surface charge are attracted to it and neutralize the charge. According to the principle of operation, neutralizers are divided into the following types: corona discharge(induction and high voltage), radioisotope, the action of which is based on the ionization of air by alpha-radiation of plutonium-239 and beta-radiation of promethium-147, aerodynamic, representing an expansion chamber, in which ions are generated by means of ionizing radiation or corona discharge, which are then supplied by an air stream to the place of formation of static electricity charges;
- reducing the intensity of static electricity. It is achieved by appropriate selection of the speed of movement of substances, excluding spraying, crushing and spraying of substances, removal of electrostatic charge, selection of friction surfaces, purification of combustible gases and liquids from impurities;
- drainage of static electricity charges that accumulate on people. This is achieved by providing workers with conductive footwear and antistatic gowns, the device of electrically conductive floors or earthed areas, platforms and work platforms. grounding of door handles, handrails of stairs, handles of devices, machines and apparatus.
Sources of magnetic field
Power frequency magnetic fields (MF) arise around any electrical installations and power frequency conductors. The higher the current, the higher the intensity of the magnetic field.
Magnetic fields can be constant, pulsed, infra-low-frequency (up to 50 Hz), and variable. The action of the MP can be continuous and intermittent.
The degree of influence of the MF depends on its maximum intensity in the working space of a magnetic device or in the zone of influence of an artificial magnet. The dose received by a person depends on the location of the workplace in relation to the MP and the mode of work. Constant MFs do not cause any subjective influences. Under the action of variable MF, characteristic visual sensations, the so-called phosphenes, are observed, which disappear at the moment of cessation of exposure.
With constant work under conditions of exposure to MF that exceed the maximum permissible levels, dysfunctions of the nervous, cardiovascular and respiratory systems, the digestive tract, and changes in the composition of the blood develop. With a predominantly local effect, vegetative and trophic disorders can occur, as a rule, in the area of the body that is under the direct influence of the MP (most often the hands). They are manifested by a sensation of itching, pallor or cyanosis of the skin, swelling and thickening of the skin, in some cases hyperkeratosis (keratinization) develops.
The strength of the MP at the workplace should not exceed 8 kA / m. The strength of a MP power transmission line with a voltage of up to 750 kV usually does not exceed 20-25 A / m, which does not pose a danger to humans.
Sources of electromagnetic radiation
Sources of electromagnetic radiation in a wide frequency range (super- and infra-low-frequency, radio-frequency, infrared, visible, ultraviolet, X-ray - Table 2) are powerful radio stations, antennas, microwave generators, induction and dielectric heating installations, radars, lasers, measuring and monitoring devices, research installations, medical high-frequency devices and devices, personal electronic computers (PC), video display terminals on cathode-ray tubes, used both in industry, scientific research, and in everyday life.
Microwave ovens, televisions, mobile phones and cordless telephones are also sources of increased electromagnetic radiation hazards.
Table 2. Spectrum of electromagnetic radiation
Low frequency radiation
Production systems are sources of low frequency radiation. transmission and distribution of electricity (power plants, transformer substations, power transmission systems and lines), power grids of residential and office buildings, electrically powered transport and its infrastructure.
With prolonged exposure to low-frequency radiation, headaches, changes in blood pressure, fatigue develop, hair loss, brittle nails, weight loss, and a persistent decrease in working capacity may occur.
To protect against low-frequency radiation, either radiation sources (Fig. 2) or areas where a person can be shielded.
Rice. 2. Shielding: a - inductor; b - capacitor
Sources of radio frequency radiation
The source of RF EMF are:
- in the range of 60 kHz - 3 MHz - unshielded elements of equipment for induction processing of metal (injection, annealing, melting, soldering, welding, etc.) and other materials, as well as equipment and devices used in radio communications and broadcasting;
- in the range 3 MHz - 300 MHz - unshielded elements of equipment and devices used in radio communications, radio broadcasting, television, medicine, as well as equipment for heating dielectrics;
- in the range 300 MHz - 300 GHz - unshielded elements of equipment and instruments used in radar, radio astronomy, radio spectroscopy, physiotherapy, etc. Long-term exposure to radio waves on various systems of the human body causes different consequences.
The most characteristic deviations in the central nervous system and the human cardiovascular system when exposed to radio waves of all ranges are. Subjective complaints - frequent headache, drowsiness or insomnia, fatigue, weakness, excessive sweating, memory loss, distraction, dizziness, darkening of the eyes, an unreasonable feeling of anxiety, fear, etc.
The influence of the electromagnetic field of the medium-wave range with prolonged exposure to is manifested in excitatory processes, violation of positive reflexes. Changes in the blood are noted, up to leukocytosis. Dysfunction of the liver, dystrophic changes in the brain, internal organs and reproductive system were found.
The short-wavelength electromagnetic field provokes changes in the adrenal cortex, cardiovascular system, bioelectrical processes of the cerebral cortex.
VHF EMF causes functional changes in the nervous, cardiovascular, endocrine and other systems of the body.
The degree of danger of exposure to a person of microwave radiation depends on the power of the source of electromagnetic radiation, the mode of operation of the emitters, design features of the emitting device, EMF parameters, energy flux density, field strength, exposure time, size of the irradiated surface, individual properties of a person, location of workplaces and efficiency protective measures.
Distinguish between thermal and biological effects of microwave radiation.
The thermal effect is a consequence of the absorption of the energy of the EMF of the microwave radiation. The higher the field strength and the longer the exposure time, the more pronounced the thermal effect. When the energy flux density is W - 10 W / m 2, the body cannot cope with heat removal, the body temperature rises and irreversible processes begin.
The biological (specific) effect is manifested in the weakening of the biological activity of protein structures, the violation of the cardiovascular system and metabolism. This effect is manifested when the intensity of the EMF is less than the thermal threshold, which is equal to 10 W / m 2.
Exposure to EMF microwave radiation is especially harmful for tissues with an underdeveloped vascular system or insufficient blood circulation (eyes, brain, kidneys, stomach, gall and bladder). Irradiation of the eyes can lead to clouding of the lens (cataracts) and burns to the cornea.
To ensure the safety of work by sources of electromagnetic waves, systematic control of the actual standardized parameters is carried out at workplaces and in places where personnel may be located. The control is carried out by measuring the strength of the electric and magnetic fields, as well as by measuring the energy flux density.
Protection of personnel from exposure to radio waves is applied in all types of work if the working conditions do not meet the requirements of the standards. This protection is carried out in the following ways:
- matched loads and power absorbers, which reduce the intensity and density of the field of the energy flux of electromagnetic waves;
- shielding the workplace and radiation source;
- rational placement of equipment in the working room;
- selection of rational modes of operation of equipment and the mode of work of personnel.
The most effective use of matched loads and power absorbers (antenna equivalents) in the manufacture, tuning and testing of individual blocks and complexes of equipment.
An effective means of protection against the effects of electromagnetic radiation is the shielding of radiation sources and the workplace with screens that absorb or reflect electromagnetic energy. The choice of the design of the screens depends on the nature of the technological process, the power of the source, and the wavelength range.
Reflective screens are made from highly conductive materials such as metals (solid walls) or cotton fabrics with a metal backing. Solid metal screens are the most effective and even at a thickness of 0.01 mm provide an attenuation of the electromagnetic field by about 50 dB (100,000 times).
For the manufacture of absorbing screens, materials with poor electrical conductivity are used. Absorbent screens are made in the form of compressed rubber sheets of a special composition with conical solid or hollow spikes, as well as in the form of porous rubber plates filled with carbonyl iron with an pressed-in metal mesh. These materials are glued to the frame or to the surface of the radiating equipment.
An important preventive measure to protect against electromagnetic radiation is the fulfillment of the requirements for the placement of equipment and for the creation of premises in which there are sources of electromagnetic radiation.
Protection of personnel from overexposure can be achieved by placing HF, UHF and UHF generators, as well as radio transmitters in specially designed rooms.
The screens of radiation sources and workplaces are blocked with disconnecting devices, which makes it possible to exclude the operation of the radiating equipment when the screen is open.
The permissible levels of exposure to workers and the requirements for monitoring at workplaces for electromagnetic fields of radio frequencies are set out in GOST 12.1.006-84.
