Bodies made of dielectrics. Active dielectrics

6. Active dielectrics.

Dielectrics, which are called active these are dielectrics, the properties of which change very much under the influence of various external factors (a factor is the driving force of a process). These dielectrics are used in various devices for energy management or for converting incoming information (in memory cells, radioelectric devices). In this regard, the requirements for active dielectrics are reversed: they must greatly change their properties, electrical characteristics, even with small external influences. The greater the response to external influence, the better such a dielectric will perform its functions.
Active dielectrics include ferroelectrics, piezoelectrics, electrets
Ferroelectrics- these are dielectrics with spontaneous (spontaneous) polarization, the direction of which can be changed using an external electric field. This is the so-called domain polarization, when the direction of the vectors of spontaneous polarization of particles in one domain is the same, but different domains are different. When exposed to an external electric field, the direction of the spontaneous polarization vectors of different domains begins to change in the direction of the external electric field, but this process of reorientation of the spontaneous polarization vectors proceeds in a non-linear dependence on the electric field strength. This dependence of electric induction on the strength of an external electric field, by analogy with magnetic induction, is called dielectric hysteresis loop.
The permittivity of such dielectrics can reach ultrahigh values ​​- several thousand units. However, the permittivity of ferroelectrics depends very strongly on temperature—usually, it is maximum in a certain temperature range and much less outside this range. Such a strong dependence of εr on temperature is a significant disadvantage of ferroelectrics.
Ferroelectrics include Rochelle salt (these dielectrics are named after Seignet, the French pharmacist who discovered the salt), barium titanate, and hundreds of other substances that have different types of chemical bonding, structural structure, and physical properties. Due to the large values ​​of εr, miniature capacitors are made from ferroelectrics with different electrical properties that determine the scope.
Known:
- teaconds - based on titanium ceramics (TiO2)
- variconds - materials with pronounced non-linear properties, that is, a strong dependence of εr on the strength of an external electric field) - they are used to make non-linear capacitors used in counting devices, in automation and radio engineering.
Piezoelectrics- from the Greek "pressure" - these are dielectrics with a piezoelectric effect, that is, as a result of pressure or mechanical stress, the dielectric is polarized and electric charges are formed on its surface. These charges are proportional to the mechanical stress, change sign with it, and disappear when it is removed. Each piezoelectric is an electromechanical transducer. Piezoelectric single crystals (quartz, tourmaline, Rochelle salt) and piezoelectric ceramics (mainly based on barium titanate) are used. They are used for electro-acoustic devices, in ultrasonic technology, in radio engineering filters, sound recording and sound recording equipment, in electronic pressure sensors.
electret a dielectric body is called, which retains polarization for a long time and creates an electric field in the space surrounding it after the removal of the external electric field. The electric field of an electret can be very strong. There are several types of electrets (according to the method of obtaining):
- thermoelectrics (the melt is cooled in an external electric field)
- photoelectrets (simultaneous exposure to light and electric field)
- corona electrets (in a corona discharge at reduced pressure).
Electrets are made from organic substances (waxes, sugars), inorganic substances (ceramics) and alkali halide crystals.
Electrets can store an electric field for years, but quickly lose their properties with increasing temperature and humidity.
Electrets are sources of a constant electric field, used in various devices: in electrophotography, electret microphones and telephones, in electronic memory elements, etc. Electrets can be obtained from almost all known dielectrics.
Pyroelectrics– they change the value of spontaneous polarization with a change in temperature. Unlike ferroelectrics, the directions of their spontaneous polarization cannot be changed by an external electric field. When the temperature changes, the spontaneous polarization changes, and a current appears in the electrical circuit. Used in thermal sensors.
A number of ferroelectrics have electro-optical effect- they change the refractive index of the medium under the action of an external electric field, which is used in lasers [optical quantum generators - sources of optical (coherent) radiation with a certain wavelength, with a high degree of directivity] for modulation (change) of laser radiation. In addition, ferroelectrics are used to create the working body of lasers - lasers that emit light of a constant wavelength. Of course, these are different materials.
There are a lot of ferroelectrics, they have a variety of properties, due to which their application is extremely diverse in modern technology.

DIELECTRIC BODIES

DIELECTRIC BODIES

otherwise, insulators, that is, bodies that do not conduct electricity, are not a conductor.

A complete dictionary of foreign words that have come into use in the Russian language. - Popov M., 1907 .

DIELECTRIC BODIES

non-conductive electricity, insulators.

, 1907 .

INSULATORS OR DIELECTRIC BODIES

in general, all bodies that conduct electricity badly and serve to insulate conductors; in particular, glass or porcelain glasses are called by this name, upotr. on the telegraph line to insulate the wire at the points of attachment to the poles.

Dictionary of foreign words included in the Russian language. - Pavlenkov F., 1907 .


See what "DIELECTRIC BODIES" are in other dictionaries:

    The name given by Michael Faraday to bodies that do not conduct, or otherwise poorly conduct electricity, such as air, glass, various resins, sulfur, etc. Such bodies are also called insulators. Before Faraday's research, carried out in 30 ... ...

    The name given by Michael Faraday to bodies that are non-conductive or, otherwise, badly conduct electricity, such as air, glass, various resins, sulfur, etc. Such bodies are also called insulators. Before Faraday's research, carried out in the 30s ... ... Encyclopedia of Brockhaus and Efron

    Bad conductors of electricity and therefore used to insulate conductors. Dictionary of foreign words included in the Russian language. Chudinov A.N., 1910. INSULATORS OR DIELECTRIC BODIES in general, all bodies that conduct poorly ... ... Dictionary of foreign words of the Russian language

    Substances that conduct electricity poorly. The term "D." (from Greek diá through and English electric electric) was introduced by M. Faraday (See Faraday) to designate substances through which electric fields penetrate. In any substance... Great Soviet Encyclopedia

    ULTRA SHORT WAVES- were first used in the therapy of Schlipgake (Schliephake). Alternating currents used in diathermy are characterized by a frequency of 800,000 to 1 million oscillations per second at a wavelength of 300-400 m. Currently, currents with a frequency of 10 ... Big Medical Encyclopedia

    electric- 3.45 electrical [electronic, programmable electronic]; E / E / PE (electrical / electronic / programmable electronic; E / E / PE) based on electrical and / or electronic and / or programmable electronic technology. Source … Dictionary-reference book of terms of normative and technical documentation

    encyclopedic Dictionary F. Brockhaus and I.A. Efron

    One of the divisions of the doctrine of electrical phenomena, which includes the study of the distribution of electricity, provided that it is in equilibrium, on bodies and the determination of those electrical forces that arise in this case. The foundation of E. was laid by the work ... ... Encyclopedic Dictionary F.A. Brockhaus and I.A. Efron

    Classical electrodynamics ... Wikipedia

    Classical electrodynamics The magnetic field of a solenoid Electricity Magnetism Electrostatics Coulomb's law ... Wikipedia

Books

  • Fundamental principles of the processes of chemical deposition of films and structures for nanoelectronics , Team of authors , The monograph presents the results of the development of chemical vapor deposition processes of metal and dielectric films using non-traditional volatile initial… Category: Technical Literature Series: Integration projects of the SB RAS Publisher: Federal State Unitary Enterprise "Publishing House of the Siberian Branch of the Russian Academy of Sciences", electronic book(fb2, fb3, epub, mobi, pdf, html, pdb, lit, doc, rtf, txt)
  • Solid State Physics for Engineers Tutorial , Gurtov V. , Osaulenko R. , Tutorial is a systematic and accessible presentation of the course of physics solid body, containing the basic elements of condensed matter physics and its applications for ... Category:

DEFINITION, PURPOSE AND CLASSIFICATION

ELECTRICAL INSULATING MATERIALS

Dielectrics- substances in which electrostatic fields can exist for a long time. These materials, in contrast to conductors, practically do not conduct electric current under the action of a constant voltage applied to them.

The purpose of electrical insulation is primarily to prevent the passage of current in ways that are undesirable for the operation of an electrical device. In addition, dielectrics in electrical devices, in particular capacitors, play an active role, providing the capacitance of the required value.

Dipole dielectrics are those whose molecules are built in space asymmetrically; they generally have a higher permittivity than neutral dielectrics. Dipole dielectrics are more hygroscopic and more easily wetted by water than neutral dielectrics.

Dielectrics are also divided into heteropolar (ionic), whose molecules are relatively easy to split into oppositely charged parts (ions), and homeopolar, not split into ions.

According to the chemical composition, electrical insulating materials are divided into organic, in containing carbon, and inorganic, not containing carbon. Usually, inorganic materials have higher heat resistance, than organic.

ELECTRICAL CONDUCTIVITY OF DIELECTRIC

By their very purpose, dielectrics under the influence of a constant voltage should not pass current at all, i.e., they should be non-conductors. However, all practically used electrical insulating materials, when a constant voltage is applied, pass some insignificant current, the so-called leakage current. Thus, the resistivity of electrical insulating materials is not infinite, although it is very large.

Resistance section of insulation is equal to the ratio of the DC voltage applied to this section of insulation U (in volts) to leakage current I(in amperes) through this section:

Insulation conductivity

.

Distinguish volume resistance isolation R V , numerically determining the obstacle created by the insulation to the passage of current through its thickness, and surface resistanceR S which determines the obstacle to the passage of current along the surface of the insulation and characterizes the presence of increased conductivity of the surface layer of the dielectric due to moisture, pollution, etc.

Impedance insulation is defined as the result of two resistances connected in parallel between the electrodes, volumetric and surface:

For a flat section of insulation with a cross section S[cm 2 ] and thickness h[cm] volume resistance (excluding edge effects) is:

.

Numerically ρ V equals the resistance (in ohms) of a cube with an edge of 1 cm from a given material, if the current passes through two opposite faces of the cube:

.

1 Ohm∙cm= 10 4 Ohm∙mm 2 /m= 10 6 µOhm∙cm= 10 -2 Ohm∙m.

The reciprocal of the volume resistivity

,

called specific volume conductivity material.

Values ρ V practically used solid and liquid electrical insulating materials range from approximately 10 8 -10 10 Ohm∙cm for relatively low-quality materials used in low-responsibility cases (wood, marble, asbestos cement, etc.) up to 10 16 -10 18 Ohm∙cm for materials such as amber, polystyrene, polyethylene, etc. For non-ionized gases ρ V about 10 19 -10 20 Ohm∙cm. The ratio of the specific resistances of a high-quality solid dielectric and a good conductor (at normal temperature) is expressed by a colossal number - about 10 22 -10 24 .

Specific surface resistanceρ S characterizes the property of an electrically insulating material to create surface resistance in the insulation made from it. Surface resistance (neglecting the influence of the edges) between electrodes with straight edges parallel to each other with a length b, at a distance from each other a, with the exclusion of the volumetric leakage current through the thickness of the material is equal to , where .

Value ρ S numerically equal to the resistance of a square (of any size) on the surface of a given material , sat current is supplied to the electrodes limiting the two opposite sides of this square .

The physical nature of the electrical conductivity of dielectrics

The electrical conductivity of dielectrics is explained by the presence in them of free (i.e., not associated with certain molecules and able to move under the action of an applied electric field) charged particles: ions, molions (colloidal particles), sometimes electrons.

Most characteristic of most electrical insulating materials ionic conductivity. It should be noted that in a number of cases the basic substance of the dielectric undergoes electrolysis; an example is glass, in which, due to its transparency, the evolution of electrolysis products can be directly observed. When a direct current is passed through glass heated to reduce conductivity, characteristic tree-like deposits (“dendrites”) of the metals that make up the glass, primarily sodium, form at the cathode. Even more often, such cases are observed when the molecules of the basic substance of the dielectric do not have the ability to easily ionize, but ionic electrical conductivity takes place due to impurities almost inevitably present in the dielectric - impurities of moisture, salts, acids, alkalis, etc. Even very small, sometimes with impurities that are difficult to detect by chemical analysis can significantly affect the conductivity of a substance; Therefore, in the manufacture of dielectrics and in general in the technique of electrical insulation, the purity of the starting products and the cleanliness of the workplace are of such great importance. For a dielectric with an ionic character of electrical conductivity, Faraday's law is strictly observed, that is, the proportionality between the amount of electricity passed through the insulation (at direct current) and the amount of the substance released during electrolysis.

With an increase temperature the specific resistance of electrical insulating materials, as a rule, is greatly reduced. It is obvious that the operating conditions of the electrical insulation become more difficult in this case. At low temperatures, on the contrary, even very poor dielectrics acquire high values ρ V .

The presence of even small amounts of water can significantly reduce ρ V dielectric. This is due to the fact that the impurities present in water dissociate into ions, or the presence of water can contribute to the dissociation of the molecules of the substance itself. Thus, the operating conditions of electrical insulation become heavier and, when hydration. Humidity has a strong influence on the change ρ V fibrous and some other materials in which moisture can form continuous films along the fibers - "bridges" penetrating the entire dielectric from one electrode to another.

Hygroscopic materials for protection against moisture after drying are impregnated or coated with non-hygroscopic varnishes, compounds, etc. When drying electrical insulation, moisture is removed from it, and its resistance increases. Therefore, as the temperature rises ρ V wetted material may even increase at first (if the effect of moisture removal outweighs the effect of temperature increase), and only after a significant part of the moisture has been removed does the decrease begin. ρ V .

The insulation resistance may decrease with voltage increase, which is of significant practical importance: by measuring the insulation resistance (of a machine, cable, capacitor, etc.) at a voltage that is lower than the operating voltage, we can get an overestimated resistance value.

addiction R from on the magnitude of the voltage due to a number of reasons:

    the formation of space charges in the dielectric;

    poor contact between the electrodes and the measured insulation, etc.

At sufficiently high intensities, electrons can be released by the forces of the electric field; the additional electronic conductivity created in this case leads to a significant increase in the total electrical conductivity. This phenomenon precedes the development of dielectric breakdown.

When a constant voltage is applied to a solid dielectric, in most cases the current gradually decreases with time, asymptotically approaching a certain steady value. Thus, gradually the conductivity of the dielectric increases, and the resistance decreases. The change in conductivity with time is associated with the influence of the formation of space charges, with the processes of electrolysis in the dielectric, and other reasons.

The nature of the change in specific surface resistance ρ S dielectrics on various factors (temperature, humidity, voltage value, time of exposure to voltage) is similar to the nature of the change ρ V discussed above. Value ρ S hygroscopic dielectrics are highly sensitive to moisture.

Polarization of dielectrics

The most important property of dielectrics is their ability to polarize under the action of an externally applied electric voltage. Polarization is reduced to a change in the spatial position of the charged material particles of the dielectric, and the dielectric acquires induced electric moment, and it generates an electric charge. If we consider some section of insulation with electrodes to which voltage is applied U [B], then the charge of this section Q [Cl] is defined by the expression

Q= CU .

Here With is the capacitance of a given section of insulation, measured in farads (f).

The capacitance of the insulation depends both on the material (dielectric) and on the geometric dimensions and configuration of the insulation.

The ability of a given dielectric to form an electrical capacitance is called its permittivity and denoted ε . Value ε vacuum is taken as a unit.

Let be With about- the capacity of the vacuum condenser of arbitrary shape and size. If, without changing the size, shape and relative position of the capacitor plates, fill the space between its plates with a material with a dielectric constant ε , then the capacitance of the capacitor will increase and reach the value

C=ε C about .

Thus, the permittivity of a substance is a number showing how many times the capacitance of a vacuum capacitor will increase if, without changing the size and shape of the capacitor electrodes, the space between the electrodes is filled with this substance. The capacitance of a capacitor of given geometric dimensions and shape is directly proportional to ε dielectric.

The value of the permittivity is included in many basic equations of electrostatics. Yes, by law Coulomb the force of mutual repulsion of two point electric charges magnitude Q 1 and Q 2 (absolute units of charge) located in a medium with permittivity ε at a distance from each other h[cm] , is:

The dielectric constant is a dimensionless quantity. For gases, it is very close to 1. Thus, for air under normal conditions ε= 1.00058. For most liquid and solid electrical insulating materials ε – of the order of several units, less often tens and very rarely exceeds 100. Some substances of a special class - ferroelectrics - under certain conditions have exceptionally high values ​​of the dielectric constant.

The physical essence of polarization

Polarization, like conduction, is due to the movement of electric charges in space. The difference between these two phenomena:

    during polarization there is a shift related with certain molecules of charges that cannot go beyond a given molecule, while conductivity is due to the movement (drift) of free charges that can move in a dielectric over a relatively long distance;

    shift during polarization - elastic shift of charges; at the end of the action of the voltage applied to the dielectric, the displaced charges tend to return to their original positions, which is not typical for conductivity;

    polarization of a homogeneous material occurs in almost all dielectric molecules, while the electrical conductivity of dielectrics is often due to the presence of a small amount of impurities (contaminants).

While the conduction current exists all the time while a constant voltage is applied to the dielectric from the outside, bias current (capacitive current) occurs only when the DC voltage is turned on or off, or in general when the magnitude of the applied voltage changes; for a long time there is a capacitive current only in a dielectric that is under the influence of AC voltage.

The most typical types of polarization are electronic, ionic and dipole.

Electronic polarization- displacement of electron orbits relative to the atomic nucleus. When an external electric field is applied, electronic polarization proceeds in an extremely short time (on the order of 10 -15 sec).

Ionic polarization(for ionic dielectrics) - displacement relative to each other of the ions that make up the molecule. This polarization proceeds in terms longer than electronic, but also in a very short time - about 10 -13 sec.

Electronic and ionic polarization - varieties deformation polarization, which is a shift of charges relative to each other in the direction of an external electric field.

Dipole (orientation) polarization is reduced to the rotation (orientation) of the dipole molecules of the substance. This polarization is numerically large compared to the deformation polarization and proceeds completely over time intervals that are different for molecules of different substances, but much longer than the duration of the deformation polarization.

It is obvious that only deformation polarization can take place in neutral dielectrics. These dielectrics have a relatively low dielectric constant (for example, for liquid and solid hydrocarbons ε about 1.9-2.8).

Table 1.1

The value of the dielectric constant of some substances

Dipole dielectrics, in which, in addition to deformation polarization, orientational polarization is also observed, have higher values ​​of permittivity compared to neutral dielectrics, and for dipole dielectrics, for example, for water, ε = 82.

The dielectric constant of a dipole substance, generally speaking, is the greater, the smaller the size of the molecule (or molecular weight). Yes, very large ε water is due to the very small size of its molecule.

Frequency dependence of permittivity. Since the time for establishing the deformation polarization is very short compared to the time for changing the sign of the voltage even at the highest frequencies used in modern radio electronics, the polarization of neutral dielectrics has time to fully establish itself in a time that can be neglected compared to the half-cycle of the alternating voltage. Therefore, a practically significant dependence ε on frequency neutral dielectrics do not.

For dipole dielectrics, with an increase in the frequency of the alternating voltage, the value ε at first also remains unchanged, but starting from some critical frequency, when the polarization does not have time to fully establish itself in one half-cycle, ε begins to decrease, approaching at very high frequencies the values ​​characteristic of neutral dielectrics; as the temperature rises, the critical frequency increases.

In sharply inhomogeneous dielectrics, in particular in dielectrics interspersed with water, the phenomenon of the so-called interlayerNoah polarization. Interlayer polarization is reduced to the accumulation of electric charges at the dielectric interfaces (in the case of a wetted dielectric, on the surface of the interspersed water). The processes of establishing interlayer polarization are very slow and can take minutes or even hours. Therefore, the increase in the capacitance of the insulation due to the moisture of the latter is the greater, the lower the frequency of the alternating voltage applied to the insulation.

Headdependence of the permittivity on temperature. For neutral dielectrics ε weakly depends on temperature, decreasing with an increase in the latter due to the thermal expansion of the substance, i.e., a decrease in the number of polarizable molecules per unit volume of the substance.

In dipole dielectrics at low temperatures, when the substance has a high viscosity, the orientation of the dipole molecules along the field is in most cases impossible or, in any case, difficult. With an increase in temperature and a decrease in viscosity, the possibility of dipole orientation becomes easier, as a result of which ε increases significantly. At high temperatures, due to the enhancement of thermal chaotic thermal vibrations of molecules, the degree of orderliness of the orientation of molecules decreases, which again leads to a decrease in ε .

In crystals with ionic polarization, glasses, porcelain and other types of ceramics with a high content of the vitreous phase, the dielectric constant increases with increasing temperature.

Conductor- this is a body, inside which contains a sufficient amount of free electric charges that can move under the influence of an electric field. In conductors, an electric current can occur under the action of an applied electric field. All metals, solutions of salts and acids, moist soil, the bodies of people and animals are good conductors of electrical charges.

dielectric or insulator- a body that does not contain free electric charges inside. In insulators, electric current is not possible.

Dielectrics include - glass, plastic, rubber, cardboard, air. bodies made of dielectrics are called insulators. Absolutely non-conductive liquid - distilled, i.e. purified water. (any other water (tap or sea) contains some amount of impurities and is a conductor)

Polarization of a dielectric in an electric field- displacement of positive and negative charges in opposite directions, i.e. orientation of molecules.

The physical parameter that characterizes the dielectric is the permittivity. The permittivity may have dispersion.

Dielectrics include air and other gases, glass, various resins, and plastics are necessarily dry. Chemically pure water is also a dielectric.

Dielectrics are used not only as insulating materials.

Conductors and insulators differ from each other in how they conduct electricity. Conductors such as copper conduct current easily, while insulators (glass) only conduct current at high voltages. Conductors and insulators are used to control current. For example, a conductor is used in a lightning rod, causing lightning to hit the ground without causing damage. Insulators are used in switches to protect people.

If the device must conduct current, then it contains conductors with low resistance. Most electrical wires are made from metals that conduct electricity well. Most often, conductors are made of copper, this metal has high conductivity (low resistance).

When current flows through a wire, it encounters resistance. This causes the conductor to heat up. If an electrical device is used as a heater, it contains high resistance conductors such as thin nickel or chromium wire.

The conductivity and resistivity of a wire depend on its thickness. Thin wires have little conductivity (high resistance) compared to thick wires made from the same material.

Thin wires are used in low-voltage networks, for example, in telephones. Thicker conductors are designed for high currents - for example, powering an electric stove.

A conductor is a body that contains a sufficient amount of free electric charges that can move under the influence of an electric field.
In conductors, an electric current can occur under the action of an applied electric field.
All metals, solutions of salts and acids, moist soil, the bodies of people and animals are good conductors of electrical charges.

An insulator (or dielectric) is a body that does not contain free electric charges inside.
In insulators, electric current is not possible.
Dielectrics include - glass, plastic, rubber, cardboard, air. bodies made of dielectrics are called insulators.
Absolutely non-conductive liquid - distilled, i.e. purified water,
(any other water (tap or sea) contains some amount of impurities and is a conductor)

ELECTRIC CURRENT IN METALS

In metal there is always a large number of free electrons.
Electric current in metal conductors is an ordered movement of free electrons under the action of an electric field created by a current source.


ELECTRIC CURRENT IN LIQUIDS

Electric current can be carried out by solutions of salts and acids, as well as ordinary water (except distilled).
A solution that can conduct electricity is called an electrolyte.
In solution, the molecules of the solute are converted into positive and negative ions by the action of the solvent. Ions under the action of an electric field applied to the solution can move: negative ions - to the positive electrode, positive ions - to the negative electrode.
An electric current is generated in the electrolyte.
When current passes through the electrolyte, pure substances contained in the solution are released on the electrodes. This phenomenon is called electrolysis.
As a result of the action of an electric current, irreversible chemical changes occur in the electrolyte, and in order to further maintain the electric current, it must be replaced with a new one.

INTERESTING

In the 17th century, after William Gilbert established that many bodies have the ability to become electrified when they are rubbed, it was believed in science that all bodies in relation to electrification are divided into two types: those capable of being electrified by friction, and bodies that are not electrified by friction .
It was not until the first half of the 18th century that certain bodies were found to possess, in addition, the ability to propagate electricity. The first experiments in this direction were carried out by the English physicist Gray. In 1729 Gray discovered the phenomenon of electrical conduction. He found that electricity can be transmitted from one body to another through a metal wire. Electricity did not spread along the silk thread. It was Gray who divided substances into conductors and non-conductors of electricity. Only in 1739. it was finally established that all bodies should be divided into conductors and dielectrics.
___

By the beginning of the 19th century, it became known that the discharge of electric fish passes through metals, but does not pass through glass and air.


DO YOU KNOW

Electroplating.

Coating objects with a layer of metal using electrolysis is called electroplating. It is possible to metallize not only metal objects, but also objects made of wood, plant leaves, lace, dead insects. First you need to make these objects hard, and for this, hold them for some time in molten wax.
Then evenly cover with a layer of graphite (for example, by rubbing with a pencil lead) to make them conductive and lower them as an electrode into a galvanic bath with electrolyte, passing through it for some time el. current. After some time, the metal contained in the solution will stand out on this electrode and evenly cover the object.

Archaeological excavations dating back to the time of the Parthian kingdom allow us to assume that galvanic gilding and silvering of products was carried out two thousand years ago!
This is evidenced by the finds made in the tombs of the Egyptian pharaohs.


EXPERIMENTS WITH ELECTROLYTES

1. If you take a solution of copper sulfate, assemble an electrical circuit and lower the electrodes (graphite rods from a pencil) into the solution, then the light will light up. There is a current!
Repeat the experiment, replacing the electrode connected to the minus of the battery with an aluminum button. After some time, it will become "golden", i.e. covered with copper. This is the phenomenon of electroplating.

2. We will need: a glass with a strong solution of table salt, a flashlight battery, two pieces of copper wire about 10 cm long. Clean the ends of the wire with fine sandpaper. Connect one end of the wires to each pole of the battery. Dip the free ends of the wires into a glass of solution. Bubbles rise near the lowered ends of the wire!


DO IT YOURSELF!

1. Make a measuring device - a tester to determine whether a substance is a conductor of electric current. To do this, you need a battery, a lamp from a flashlight and connecting wires. Close the assembled electrical circuit to the conductor under study and, by the presence or absence of the glow of the lamp, determine whether the substance is a conductor.

2. You can demonstrate the presence of free electric charges in a liquid as follows: connect a metal kettle and an aluminum glass from the calorimeter with conductors to the galvanometer. Pour water into the kettle, in which you dissolve a little salt. Start pouring salt water from the kettle into a glass in a thin stream, the galvanometer will show the presence of an electric current. By changing the length and thickness of the jet, follow the change in the current strength.


With a grounding device, it is good to bury the wire to a depth of 2.5 m. However, in the field
doing so is not always possible. Therefore, grounding is often done in the form of a pin hammered into the ground. Why is it useful to pour salt water over the grounding point in this case?


NO-I-I!

In the event of a fire in electrical installations, turn off the breaker immediately. The fire caused by the current CANNOT be extinguished with water or a conventional fire extinguisher, because. the water jet is a conductor and can close the circuit again and restore the cause of the fire. In this case, it is necessary to use dry sand or a sandblast fire extinguisher.


THE HUMAN BODY IS A CONDUCTOR OF ELECTRICITY

If a person accidentally becomes energized, injury or even death is possible.

When working with electrical circuits, DO NOT:
- Do not touch bare wires with both hands at the same time.
- do not touch a bare wire while standing on the ground or on a damp (even cement or wooden) floor.
- Do not use faulty electrical appliances.
- Do not repair an electrical device without disconnecting it from the power source.

First aid for an electric shock.

Often the person himself cannot get rid of the wires with current, because. the electric current causes a convulsive contraction of the muscles, or the victim loses consciousness. First you need to disconnect the person from the current-carrying wires. To do this, turn off the current or unscrew the fuses near the meter. If the switch is far away, then it is necessary to pull it away from the wire with a wooden stick (non-conductive object). Underfoot should be an insulating surface: a rubber mat, dry boards or linoleum. It is possible to drag the victim away from the wires with bare hands only by the ends of dry clothes and with one hand. You can not touch those connected to the ground. conductive objects!
Then the victim should be put on his back and a doctor should be called.

Don't put your fingers in the socket, they'll come in handy!

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