The phenomenon of electromagnetic current induction: the essence, who discovered
The word "induction" in Russian means the processes of excitation, guidance, creation of something. In electrical engineering, this term has been used for more than two centuries.
After getting acquainted with the publications of 1821, describing the experiments of the Danish scientist Oersted on the deviations of the magnetic needle near the conductor with electric shock, Michael Faraday set himself the task of: convert magnetism to electricity.
After 10 years of research, he formulated the basic law electromagnetic induction, explaining that inside any closed circuit, an electromotive force is induced. Its value is determined by the rate of change magnetic flux penetrating the contour under consideration, but taken with a minus sign.
Broadcast electromagnetic waves at a distance
The first guess that dawned on the brain of a scientist was not crowned with practical success.
He placed two closed conductors side by side. Near one I installed a magnetic needle as an indicator of the passing current, and in the other wire I applied a pulse from a powerful galvanic source of that time: a volt column.
The researcher assumed that with a current pulse in the first circuit, the changing magnetic field in it would induce a current in the second conductor, which would deflect the magnetic needle. But, the result was negative - the indicator did not work. Or rather, he lacked sensitivity.
The scientist's brain foresaw the creation and transmission of electromagnetic waves over a distance, which are now used in radio broadcasting, television, wireless control, Wi-Fi technologies and similar devices. He was simply let down by the imperfect element base of the measuring devices of that time.
Power generation
After an unsuccessful experiment, Michael Faraday modified the conditions of the experiment.
For the experiment, Faraday used two coils with closed circuits. In the first circuit, he supplied an electric current from a source, and in the second he observed the appearance of an EMF. The current passing through the turns of winding No. 1 created a magnetic flux around the coil, penetrating winding No. 2 and forming an electromotive force in it.
During Faraday's experiment:
- turned on the pulse supply of voltage to the circuit with stationary coils;
- when the current was applied, he injected the upper one into the lower coil;
- permanently fixed winding No. 1 and introduced winding No. 2 into it;
- change the speed of movement of the coils relative to each other.
In all these cases, he observed the manifestation of the induction emf in the second coil. And only when passing direct current there was no electromotive force on winding No. 1 and fixed coils.
The scientist determined that the EMF induced in the second coil depends on the speed at which the magnetic flux changes. It is proportional to its size.
The same pattern is fully manifested when a closed loop passes through. Under the action of the EMF, an electric current is formed in the wire.
The magnetic flux in the case under consideration changes in the circuit Sk created by a closed circuit.
In this way, the development created by Faraday made it possible to place a rotating conductive frame in a magnetic field.
It was then made from a large number of turns, fixed in rotation bearings. At the ends of the winding, slip rings and brushes sliding along them were mounted, and a load was connected through the leads on the case. The result is a modern alternator.
Its over simple design was created when the winding was fixed on a stationary case, and the magnetic system began to rotate. In this case, the method of generating currents at the expense was not violated in any way.
The principle of operation of electric motors
The law of electromagnetic induction, which was substantiated by Michael Faraday, made it possible to create various designs electric motors. They have a similar device with generators: a movable rotor and a stator, which interact with each other due to rotating electromagnetic fields.
Electricity transformation
Michael Faraday determined the occurrence of an induced electromotive force and an induction current in a nearby winding when changing magnetic field in the adjacent coil.
The current inside the nearby winding is induced by switching the switch circuit in coil 1 and is always present during the operation of the generator on winding 3.
On this property, called mutual induction, the operation of all modern transformer devices is based.
To improve the passage of the magnetic flux, they have insulated windings put on a common core, which has a minimum magnetic resistance. It is made from special grades of steel and formed in typesetting thin sheets in the form of sections of a certain shape, called a magnetic circuit.
Transformers transmit alternating energy by mutual induction. electromagnetic field from one winding to another so that in this case there is a change, a transformation of the magnitude of the voltage at its input and output terminals.
The ratio of the number of turns in the windings determines transformation ratio, and the thickness of the wire, the design and volume of the core material - the amount of transmitted power, the operating current.
Work of inductors
The manifestation of electromagnetic induction is observed in the coil during a change in the magnitude of the current flowing in it. This process is called self-induction.
When the circuit breaker is turned on in the above diagram induction current modifies the nature of the rectilinear increase in the operating current in the circuit, as well as during a trip.
When an alternating voltage, not a constant voltage, is applied to a conductor wound into a coil, the current value reduced by the inductive resistance flows through it. The energy of self-induction shifts the phase of the current with respect to the applied voltage.
This phenomenon is used in chokes, which are designed to reduce the large currents that occur when certain conditions equipment operation. Such devices, in particular, are used.
Design feature of the magnetic circuit at the inductor - a cut of the plates, which is created to further increase the magnetic resistance to the magnetic flux due to the formation of an air gap.
Chokes with a split and adjustable position of the magnetic circuit are used in many radio engineering and electrical devices. Quite often they can be found in designs welding transformers. They reduce the magnitude of the electric arc passed through the electrode to the optimum value.
Induction Furnaces
The phenomenon of electromagnetic induction manifests itself not only in wires and windings, but also inside any massive metal objects. The currents induced in them are called eddy currents. During the operation of transformers and chokes, they cause heating of the magnetic circuit and the entire structure.
To prevent this phenomenon, the cores are made of thin metal sheets and insulated between themselves with a layer of varnish that prevents the passage of induced currents.
In heating structures, eddy currents do not limit, but create the most favorable conditions for their passage. widely used in industrial production to create high temperatures.
Electrical measuring devices
A large class of induction devices continues to operate in the energy sector. Electric meters with a rotating aluminum disc, similar to the design of the power relay, sedative systems pointer measuring instruments operate on the basis of the principle of electromagnetic induction.
Gas magnetic generators
If, instead of a closed frame, a conductive gas, liquid or plasma is moved in the field of a magnet, then the charges of electricity under the action of magnetic lines of force will deviate in strictly defined directions, forming an electric current. Its magnetic field on the mounted electrode contact plates induces an electromotive force. Under its action, an electric current is created in the connected circuit to the MHD generator.
This is how the law of electromagnetic induction manifests itself in MHD generators.
There are no such complex rotating parts as the rotor. This simplifies the design, allows you to significantly increase the temperature working environment and, at the same time, the efficiency of power generation. MHD generators operate as backup or emergency sources capable of generating significant electricity flows in short periods of time.
Thus, the law of electromagnetic induction, justified by Michael Faraday at one time, continues to be relevant today.
The law of electromagnetic induction underlies modern electrical engineering, as well as radio engineering, which, in turn, forms the core of modern industry, which has completely transformed our entire civilization. Practical use electromagnetic induction began only half a century after its discovery. At that time, technological progress was still relatively slow. The reason why electrical engineering plays such an important role in all of our modern lives is because electricity is the most convenient form of energy and it is precisely because of the law of electromagnetic induction. The latter makes it easy to obtain electricity from mechanical energy (generators), to flexibly distribute and transport energy (transformers) and convert it back into mechanical energy (electric motor) and other types of energy, and all this happens with very high efficiency. Some 50 years ago, the distribution of energy between machines in factories was carried out through complex system shafts and belt drives - the forest of transmissions was characteristic detail industrial "interior" of that time. Modern machine tools are equipped with compact electric motors fed through a hidden electrical wiring system.
Modern industry uses single system electricity supply, covering the entire country, and sometimes several neighboring countries.
The power supply system starts with a power generator. The operation of the generator is based on the direct use of the law of electromagnetic induction. Schematically the simplest generator It is a stationary electromagnet (stator), in the field of which a coil (rotor) rotates. The alternating current excited in the rotor winding is removed with the help of special movable contacts - brushes. Since it is difficult to pass large power through moving contacts, an inverted generator circuit is often used: a rotating electromagnet excites current in the stationary stator windings. Thus, the generator converts the mechanical energy of the rotation of the rotor into electricity. The latter is driven by either thermal energy (steam or gas turbine) or mechanical energy (hydro turbine).
At the other end of the power supply system are various executive mechanisms that use electricity, the most important of which is an electric motor (electric motor). The most common, due to its simplicity, is the so-called asynchronous motor, invented independently in 1885-1887. Httalian physicist Ferraris and the famous Croatian engineer Tesla (USA). The stator of such an engine is a complex electromagnet that creates a rotating field. The rotation of the field is achieved using a system of windings in which the currents are phase shifted. In the simplest case, it suffices to take a superposition of two fields in perpendicular directions, shifted in phase by 90° (Fig. VI.10).
Such a field can be written as a complex expression:
which represents a two-dimensional vector of constant length, rotating counterclockwise with a frequency o. Although formula (53.1) is similar to the complex representation of alternating current in § 52, its physical meaning different. In the case of alternating current, only the real part of the complex expression had a real value, but here the complex value represents a two-dimensional vector, and its phase is not only the phase of the oscillations of the components variable field, but also characterizes the direction of the field vector (see Fig. VI.10).
In engineering, it is common to use somewhat more complex scheme rotation of the field using the so-called three-phase current, i.e. three currents, the phases of which are shifted by 120 ° relative to each other. These currents create a magnetic field in three directions, rotated one relative to the other by an angle of 120 ° (Fig. VI.11). Note that such a three-phase current is automatically obtained in generators with a similar arrangement of windings. received wide use in the technique of three-phase current was invented
Rice. VI.10. Scheme for obtaining a rotating magnetic field.
Rice. VI.11. Scheme of an asynchronous motor. For simplicity, the rotor is shown as a single turn.
in 1888 by the outstanding Russian electrical engineer Dolivo-Dobrovolsky, who built in Germany on this basis the world's first technical power line.
The rotor winding of an induction motor consists in the simplest case of short-circuited turns. An alternating magnetic field induces a current in the coils, which leads to the rotation of the rotor in the same direction as the magnetic field. In accordance with Lenz's rule, the rotor tends to "catch up" with the rotating magnetic field. For a loaded motor, the rotor speed is always less than the field, since otherwise the induction EMF and the current in the rotor would turn to zero. Hence the name - asynchronous motor.
Task 1. Find the speed of rotation of the rotor of an induction motor depending on the load.
The equation for the current in one turn of the rotor has the form
where - the angular velocity of the field sliding relative to the rotor, characterizes the orientation of the coil relative to the field, the location of the coil in the rotor (Fig. VI.12, a). Passing to complex quantities (see § 52), we obtain the solution (53.2)
The torque acting on a coil in the same magnetic field is
Rice. VI.12. To the problem of asynchronous motor. a - a turn of the rotor winding in a "sliding" field; b - load characteristic of the engine.
Usually the rotor winding contains big number evenly spaced turns, so that summation over 9 can be replaced by integration, resulting in the total torque on the motor shaft
where is the number of turns of the rotor. The dependency graph is shown in Fig. VI.12, b. The maximum torque corresponds to the slip frequency Note that the ohmic resistance of the rotor only affects the slip frequency, not the maximum motor torque. The negative slip frequency (the rotor “overtakes” the field) corresponds to the generator mode. To maintain this mode, it is necessary to expend external energy, which is converted into electrical energy in the stator windings.
For a given torque, the slip frequency is ambiguous, but only the mode is stable
The main element of the systems for converting and transporting electricity is a transformer that changes the AC voltage. For long-distance transmission of electricity, it is advantageous to use the maximum possible voltage, limited only by insulation breakdown. At present, transmission lines operate with a voltage of about For a given transmitted power, the current in the line is inversely proportional to the voltage, and the losses in the line fall as the square of the voltage. On the other hand, much lower voltages are needed to power consumers of electricity, mainly for reasons of simplicity of design (insulation), as well as safety. Hence the need for voltage transformation.
Usually the transformer consists of two windings on a common iron core (Fig. VI. 13). An iron core is needed in a transformer to reduce stray flux and therefore better flux linkage between the windings. Since iron is also a conductor, it passes a variable
Rice. V1.13. Schematic of an AC transformer.
Rice. VI.14. Scheme of the Rogowski belt. The dashed line conditionally shows the integration path.
magnetic field only to a shallow depth (see § 87). Therefore, the cores of transformers have to be made laminated, that is, in the form of a set of thin plates electrically isolated from one another. For a power frequency of 50 Hz, the usual plate thickness is 0.5 mm. For transformers at high frequencies (in radio engineering), you have to use very thin plates (mm) or ferrite cores.
Task 2. What voltage should the transformer core plates be insulated to?
If the number of plates in the core and the voltage per turn of the transformer winding, then the voltage between adjacent plates
In the simplest case of the absence of a scattered flow, the EMF ratio in both windings is proportional to the number of their turns, since the induction EMF per turn is determined by the same flux in the core. If, in addition, the losses in the transformer are small, and the load resistance is large, then it is obvious that the ratio of the voltages on the primary and secondary windings is also proportional. This is the principle of operation of the transformer, which thus makes it easy to change the voltage many times over.
Task 3. Find the voltage transformation ratio for an arbitrary load.
Neglecting losses in the transformer and leakage (ideal transformer), we write the equation for currents in the windings in the form (in SI units)
where is the complex load resistance (see § 52) and the expression (51.2) is used for the induction EMF of a complex circuit. With the help of relation (51.6); you can find the voltage transformation ratio without solving equations (53.6), but simply by dividing them one by the other:
The transformation ratio turns out to be equal, therefore, simply to the ratio of the number of turns at any load. The sign depends on the choice of the beginning and end of the windings.
To find the current transformation ratio, you need to solve the system (53.7), as a result of which we get
In the general case, the coefficient turns out to be some complex value, i.e., a phase shift appears between the currents in the windings. Of interest special case small load Then, i.e., the ratio of currents becomes the inverse of the ratio of voltages.
This transformer mode can be used to measure high currents (current transformer). It turns out that the same simple transformation of currents is also preserved for an arbitrary dependence of the current on time with a special design of the current transformer. In this case, it is called the Rogowski coil (Fig. VI.14) and is a flexible closed solenoid of arbitrary shape with uniform winding. The operation of the belt is based on the law of conservation of the circulation of the magnetic field (see § 33): where integration is performed along the contour inside the belt (see Fig. VI.14), is the total measured current covered by the belt. Assuming that the transverse dimensions of the belt are small enough, we can write the induction emf induced on the belt as follows:
where is the cross section of the belt, a is the winding density, both values are assumed to be constant along the belt; inside the belt, if the density of the winding of the belt and its cross section 50 are constant along the length (53.9).
Simple conversion electrical voltage possible only for alternating current. This determines its decisive role in modern industry. In cases where direct current is required, significant difficulties arise. For example, in ultra-long power transmission lines, the use of direct current provides significant advantages: heat loss, since there is no skin effect (see § 87) and there are no resonant
(wave) transients when turning on - off the transmission line, the length of which is of the order of the wavelength of alternating current (6000 km for an industrial frequency of 50 Hz). The difficulty lies in rectifying high voltage alternating current at one end of the transmission line and inverting it at the other.
After the discoveries of Oersted and Ampère, it became clear that electricity has a magnetic force. Now it was necessary to confirm the influence of magnetic phenomena on electrical ones. This problem was brilliantly solved by Faraday.
In 1821, M. Faraday made an entry in his diary: "Turn magnetism into electricity." After 10 years, this problem was solved by him.
So, Michael Faraday (1791-1867) - English physicist and chemist.
One of the founders of quantitative electrochemistry. First received (1823) in liquid state chlorine, then hydrogen sulfide, carbon dioxide, ammonia and nitrogen dioxide. Discovered (1825) benzene, studied its physical and some Chemical properties. Introduced the concept of dielectric permittivity. Faraday's name entered the system of electrical units as a unit of electrical capacitance.
Many of these works could, by themselves, immortalize the name of their author. But the most important of scientific works Faraday are his research in the field of electromagnetism and electrical induction. Strictly speaking, an important branch of physics that treats the phenomena of electromagnetism and induction electricity, and which is currently of such great importance for technology, was created by Faraday from nothing.
When Faraday finally devoted himself to research in the field of electricity, it was found that with ordinary conditions the presence of an electrified body is sufficient for its influence to excite electricity in every other body.
At the same time, it was known that the wire through which the current passes and which is also an electrified body does not have any effect on other wires placed nearby. What caused this exception? This is the question that interested Faraday and the solution of which led him to the most important discoveries in the field of induction electricity.
Faraday wound two insulated wires parallel to each other on the same wooden rolling pin. He connected the ends of one wire to a battery of ten elements, and the ends of the other to a sensitive galvanometer. When the current was passed through the first wire, Faraday turned all his attention to the galvanometer, expecting to notice from its oscillations the appearance of a current in the second wire. However, there was nothing of the kind: the galvanometer remained calm. Faraday decided to increase the current and introduced 120 galvanic cells into the circuit. The result is the same. Faraday repeated this experiment dozens of times, all with the same success. Anyone else in his place would have left the experiment, convinced that the current passing through the wire has no effect on the adjacent wire. But Faraday always tried to extract from his experiments and observations everything that they could give, and therefore, not having received a direct effect on the wire connected to the galvanometer, he began to look for side effects.
electromagnetic induction electric current field
He immediately noticed that the galvanometer, remaining completely calm during the entire passage of the current, began to oscillate at the very closing of the circuit, and when it was opened, it turned out that at the moment when the current was passed into the first wire, and also when this transmission ceased, during the second wire is also excited by a current, which in the first case has the opposite direction with the first current and is the same with it in the second case and lasts only one instant.
Being instantaneous, instantly disappearing after their appearance, inductive currents would have no practical value, if Faraday had not found a way, with the help of an ingenious device (switch), to constantly interrupt and again conduct the primary current coming from the battery through the first wire, due to which more and more inductive currents are continuously excited in the second wire, thus becoming constant. So a new source was found electrical energy, in addition to previously known (friction and chemical processes), - induction, and the new kind of this energy is induction electricity.
ELECTROMAGNETIC INDUCTION(lat. inductio - guidance) - the phenomenon of generating a vortex electric field alternating magnetic field. If a closed conductor is introduced into an alternating magnetic field, then an electric current will appear in it. The appearance of this current is called current induction, and the current itself is called inductive.
Khudoley Andrey, Khnykov Igor
Practical application of the phenomenon of electromagnetic induction.
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Electromagnetic induction in modern technology Performed by students of 11 "A" class MOUSOSH No. 2 of the city of Suvorov Khnykov Igor, Khudoley Andrey
The phenomenon of electromagnetic induction was discovered on August 29, 1831 by Michael Faraday. The phenomenon of electromagnetic induction consists in the occurrence of an electric current in a conducting circuit, which either rests in a magnetic field that changes in time, or moves in a constant magnetic field in such a way that the number of magnetic induction lines penetrating the circuit changes.
The EMF of electromagnetic induction in a closed loop is numerically equal and opposite in sign to the rate of change of the magnetic flux through the surface bounded by this loop. The direction of the induction current (as well as the magnitude of the EMF) is considered positive if it coincides with the selected direction of bypassing the circuit.
Faraday's experiment A permanent magnet is inserted into or removed from a coil connected to a galvanometer. When the magnet moves in the circuit, an electric current arises. Within one month, Faraday experimentally discovered all the essential features of the phenomenon of electromagnetic induction. At present, Faraday's experiments can be carried out by anyone.
The main sources of the electromagnetic field The main sources of the electromagnetic field are: Power lines. Wiring (inside buildings and structures). Household electrical appliances. Personal computers. TV and radio transmitting stations. Satellite and cellular communications (devices, repeaters). Electric transport. radar installations.
Power lines The wires of an operating power line create an electromagnetic field of industrial frequency (50 Hz) in the adjacent space (at distances of the order of tens of meters from the wire). Moreover, the field strength near the line can vary over a wide range, depending on its electrical load. In fact, the boundaries of the sanitary protection zone are established along the boundary line furthest from the wires of the maximum electric field strength, equal to 1 kV / m.
Electrical wiring Electrical wiring includes: power cables for building life support systems, power distribution wires, as well as branching boards, power boxes and transformers. Electrical wiring is the main source of the industrial frequency electromagnetic field in residential premises. In this case, the level of the electric field strength emitted by the source is often relatively low (does not exceed 500 V/m).
Household electrical appliances Sources of electromagnetic fields are all household appliances that operate using electric current. At the same time, the level of radiation varies over the widest range, depending on the model, the device device and the specific mode of operation. Also, the level of radiation strongly depends on the power consumption of the device - the higher the power, the higher the level of the electromagnetic field during the operation of the device. The electric field strength near household appliances does not exceed tens of V/m.
Personal Computers The main source of adverse health effects for a computer user is the monitor's display device (VOD). In addition to the monitor system block a personal computer may also include a large number of other devices (such as printers, scanners, network filters and so on.). All these devices work with the use of electric current, which means that they are sources of an electromagnetic field.
The electromagnetic field of personal computers has the most complex wave and spectral composition and is difficult to measure and quantify. It has magnetic, electrostatic and radiation components (in particular, the electrostatic potential of a person sitting in front of a monitor can range from -3 to +5 V). Given the condition that personal computers are now actively used in all industries human activity, their impact on human health is subject to careful study and control
Television and radio transmitting stations A significant number of radio broadcasting stations and centers are currently located on the territory of Russia. various accessories. Transmitting stations and centers are located in areas specially designated for them and can occupy quite large territories(up to 1000 ha). By their structure, they include one or more technical buildings, where radio transmitters are located, and antenna fields, on which up to several dozen antenna-feeder systems (AFS) are located. Each system includes a radiating antenna and a feeder line that brings the broadcast signal.
Satellite communication Satellite communication systems consist of a transmitting station on the Earth and satellites - repeaters in orbit. Transmitting satellite communication stations emit a narrowly directed wave beam, the energy flux density in which reaches hundreds of W/m. Satellite communication systems create high electromagnetic field strengths at considerable distances from antennas. For example, a station with a power of 225 kW, operating at a frequency of 2.38 GHz, creates an energy flux density of 2.8 W/m2 at a distance of 100 km. The scattering of energy relative to the main beam is very small and occurs most of all in the area of \u200b\u200bthe direct placement of the antenna.
Cellular communication Cellular radiotelephony is today one of the most intensively developing telecommunication systems. The main elements of the system cellular communication are base stations and mobile radiotelephones. Base stations maintain radio communication with mobile devices, as a result of which they are sources of an electromagnetic field. The system uses the principle of dividing the coverage area into zones, or so-called "cells", with a radius of km.
The radiation intensity of the base station is determined by the load, that is, the presence of owners cell phones in the service area of a particular base station and their desire to use the phone for a conversation, which, in turn, depends fundamentally on the time of day, the location of the station, the day of the week, and other factors. At night, the loading of stations is almost zero. The radiation intensity of mobile devices depends largely on the state of the communication channel "mobile radiotelephone - base station" (the greater the distance from the base station, the higher the radiation intensity of the device).
Electric transport Electric transport (trolleybuses, trams, subway trains, etc.) is a powerful source of electromagnetic field in the Hz frequency range. At the same time, in the overwhelming majority of cases, the traction electric motor acts as the main emitter (for trolleybuses and trams, air current collectors compete with the electric motor in terms of the intensity of the radiated electric field).
Radar installations Radar and radar installations usually have reflector-type antennas (“dishes”) and emit a narrowly directed radio beam. Periodic movement of the antenna in space leads to spatial discontinuity of radiation. There is also a temporary discontinuity of radiation due to the cyclic operation of the radar for radiation. They operate at frequencies from 500 MHz to 15 GHz, but some special installations can operate at frequencies up to 100 GHz or more. Due to the special nature of the radiation, they can create zones with a high energy flux density (100 W/m2 or more) on the ground.
Metal detectors Technologically, the principle of operation of a metal detector is based on the phenomenon of registering an electromagnetic field that is created around any metal object when it is placed in an electromagnetic field. This secondary electromagnetic field differs both in intensity (field strength) and in other parameters. These parameters depend on the size of the object and its conductivity (gold and silver have much better conductivity than, for example, lead) and, of course, on the distance between the metal detector antenna and the object itself (depth of occurrence).
The above technology determined the composition of the metal detector: it consists of four main blocks: an antenna (sometimes the emitting and receiving antennas are different, and sometimes they are the same antenna), an electronic processing unit, an information output unit (visual - LCD display or dial indicator and audio - speaker or headphone jack) and power supply.
Metal detectors are: Search Inspection For construction purposes
Search This metal detector is designed to search for all kinds of metal objects. As a rule, these are the largest in size, cost and, of course, in terms of the functions of the model. This is due to the fact that sometimes you need to find objects at a depth of up to several meters in the thickness of the earth. A powerful antenna is capable of generating a high level of electromagnetic field and detecting even the slightest currents at great depths with high sensitivity. For example, a search metal detector detects a metal coin at a depth of 2-3 meters in the earth, which may even contain ferruginous geological compounds.
Inspection cameras Used by special services, customs officers and security officers of various organizations to search for metal objects (weapons, precious metals, wires of explosive devices, etc.) hidden on the body and in the clothes of a person. These metal detectors are distinguished by compactness, ease of use, the presence of modes such as silent vibration of the handle (so that the searched person does not know that the search officer has found something). The range (depth) of detection of a ruble coin in such metal detectors reaches 10-15 cm.
Arched metal detectors, which outwardly resemble an arch and require a person to pass through it, are also widely used. Along them vertical walls laid ultra-sensitive antennas that detect metal objects at all levels of human growth. They are usually installed in front of places of cultural entertainment, in banks, institutions, etc. main feature arched metal detectors - high sensitivity (adjustable) and high speed of processing the flow of people.
For construction purposes This class of metal detectors, with the help of sound and light alarms, helps builders find metal pipes, structural elements or drives located both in the thickness of walls and behind partitions and false panels. Some metal detectors for construction purposes are often combined in one device with detectors wooden construction, voltage detectors on current-carrying wires, leakage detectors, etc.
We already know that an electric current, moving through a conductor, creates a magnetic field around it. Based on this phenomenon, man has invented and widely uses a wide variety of electromagnets. But the question arises: if electric charges, moving, cause the appearance of a magnetic field, but doesn’t it work and vice versa?
That is, can a magnetic field cause an electric current to flow in a conductor? In 1831, Michael Faraday found that in a closed conducting electrical circuit, when a magnetic field changes, an electric current arises. Such a current was called an induction current, and the phenomenon of the appearance of a current in a closed conducting circuit with a change in the magnetic field penetrating this circuit is called electromagnetic induction.
The phenomenon of electromagnetic induction
The name "electromagnetic" itself consists of two parts: "electro" and "magnetic". Electrical and magnetic phenomena are inextricably linked with each other. And if the electric charges, moving, change the magnetic field around them, then the magnetic field, changing, willy-nilly make the electric charges move, forming an electric current.
In this case, it is the changing magnetic field that causes the occurrence of an electric current. A permanent magnetic field will not cause movement electric charges, and accordingly, the induction current is not formed. A more detailed consideration of the phenomenon of electromagnetic induction, the derivation of formulas and the law of electromagnetic induction refers to the course of the ninth grade.
Application of electromagnetic induction
In this article, we will talk about the use of electromagnetic induction. The operation of many motors and current generators is based on the use of the laws of electromagnetic induction. The principle of their work is quite simple to understand.
A change in the magnetic field can be caused, for example, by moving a magnet. Therefore, if a magnet is moved inside a closed circuit by some third-party influence, then a current will appear in this circuit. So you can create a current generator.
If, on the contrary, a current from a third-party source is passed through the circuit, then the magnet inside the circuit will begin to move under the influence of the magnetic field generated by the electric current. In this way, an electric motor can be assembled.
The current generators described above convert mechanical energy into electrical energy at power plants. Mechanical energy is the energy of coal, diesel fuel, wind, water and so on. Electricity is supplied by wires to consumers and there it is converted back into mechanical energy in electric motors.
The electric motors of vacuum cleaners, hair dryers, mixers, coolers, electric meat grinders and numerous other devices that we use daily are based on the use of electromagnetic induction and magnetic forces. There is no need to talk about the use of these same phenomena in industry, it is clear that it is ubiquitous.
