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A conductor of electricity is a solid body in which there are many free electrons. Electrons can move freely in matter, but cannot leave the surface. There are so many free electrons in a metal that any electric field sets many of them in motion. And either the current of electrons that has arisen in this way must continuously maintain its existence due to external sources of energy, or the movement of electrons stops as soon as they discharge the sources that caused the field in the beginning. In terms of electrostatics, we do not consider continuous current sources (we will talk about them in magnetostatics), so the electrons move only until they are located so that zero electric field is created everywhere inside the conductor. As a rule, this happens in small fractions of a second. If there were any field left inside, it would force some more electrons to move; only such an electrostatic solution is possible, when the field is equal to zero everywhere inside.

A conductor of electricity is characterized by the fact that its electrons are very mobile.

Conductors of electricity are of two kinds - according to the nature of the movement - through them an electric current.

Conductors of electricity are bodies in which electric conduction currents can be created.

Conductors of electricity - tols, in which electric currents can occur. Electric currents can arise when carriers of electric charges exist or form in bodies. Such an ordered movement of electric charges is an electric current. In electrolytes, charge carriers are ions - parts of the molecules of the solute.

Conductors of electricity are bodies in which electric currents can be created.

Let a conductor of electricity enclosed in a tube (see fig. VIII.

Since the conductor of electricity is water contained in the pores of the rock, in order to interpret the electrical log curves, it is necessary to know the factors that affect the water resistance. Pure water does not conduct electricity. Salts dissolved in water form charged ions that carry electrons or electrical charges. The conductivity of a solution is determined by the concentration and mobility of the ions. The mobility of ions in solution depends on two factors - the nature of the ions and the temperature. Ion of everyone chemical compound has its own mobility. However, the determination of the conductivity of a solution based on chemical analysis and using data on the mobility of individual ions is impractical.

All conductors of electricity have fluctuations in electrical voltage (current), or noise. In semiconductor diodes, four main components of internal noise should be distinguished: thermal noise, shot noise, 1 / / - noise, noise in the region breakdown r-p transition on the reverse branch of the current-voltage characteristic.

Every person, constantly using electrical appliances, is faced with:

1. conductors that pass electric current;

2. dielectrics with insulating properties;

3. semiconductors that combine the characteristics of the first two types of substances and change them depending on the applied control signal.

A distinctive feature of each of these groups is the property of electrical conductivity.

What is a conductor

Conductors include those substances that have in their structure a large number of free, rather than bound, electric charges that can start moving under the influence of an applied external force. They can be in solid, liquid or gaseous state.

If you take two conductors, between which a potential difference is formed, and connect a metal wire inside them, then an electric current will flow through it. Its carriers will be free electrons, not held by the bonds of atoms. They characterize or the ability of any substance to pass through itself electric charges - current.

The value of electrical conductivity is inversely proportional to the resistance of the substance and is measured by the appropriate unit: Siemens (Sm).

1 cm=1/1 ohm.

In nature, charge carriers can be:

electrons;

ions;

holes.

According to this principle, electrical conductivity is divided into:

electronic;

ionic;

hole.

The quality of the conductor makes it possible to evaluate the dependence of the current flowing in it on the value of the applied voltage. It is customary to call it by the designation of the units of measurement of these electrical quantities - the current-voltage characteristic.

Conductors with electronic conductivity

The most common representatives of this type are metals. They create an electric current solely due to the movement of the flow of electrons.

Inside metals, they are in two states:

bound by the forces of atomic cohesion;

free.

Electrons held in orbit by the forces of attraction of the atomic nucleus, as a rule, do not participate in the creation of electric current under the action of external electromotive forces. Free particles behave differently.

If an EMF is not applied to a metal conductor, then free electrons move randomly, randomly, in any direction. Their movement is due to thermal energy. It is characterized by different speeds and directions of movement of each particle at any given time.

When the energy of an external field with a strength E is applied to the conductor, then a force directed opposite to the acting field acts on all the electrons together and each separately. It creates a strictly oriented movement of electrons, or in other words, an electric current.

The current-voltage characteristic of metals is a straight line that fits into Ohm's law for a section and a complete circuit.

In addition to pure metals, other substances also have electronic conductivity. These include:

alloys;

individual modifications of carbon (graphite, coal).

All of the above substances, including metals, are classified as conductors of the 1st kind. Their electrical conductivity is in no way connected with the transfer of the mass of a substance due to the passage of an electric current, but is determined only by the movement of electrons.

If metals and alloys are placed in a medium of ultralow temperatures, they pass into a state of superconductivity.

Conductors with ionic conductivity

This class includes substances in which an electric current is created due to the movement of charges by ions. They are classified as conductors of the second kind. This:

solutions of alkalis, acids, salts;

melts of various ionic compounds;

various gases and vapours.

Electric current in liquid

The liquid media conducting electric current, in which the transfer of matter together with charges and its deposition on the electrodes, is commonly called electrolytes, and the process itself is called electrolysis.

It occurs under the influence of an external energy field by applying a positive potential to the anode electrode and a negative one to the cathode.

Ions inside liquids are formed due to the phenomenon of electrolytic dissociation, which consists in the splitting of a part of the molecules of a substance that have neutral properties. An example is copper chloride, which aqueous solution breaks down into its constituent copper ions (cations) and chlorine (anions).

CuCl2꞊Cu2++2Cl-

Under the action of the applied voltage to the electrolyte, the cations begin to move strictly towards the cathode, and the anions - towards the anode. In this way, chemically pure copper without impurities is obtained, which is released at the cathode.

In addition to liquids, there are also solid electrolytes in nature. They are called superionic conductors (super-ionics), which have a crystalline structure and the ionic nature of chemical bonds, which cause high electrical conductivity due to the movement of ions of the same type.

The current-voltage characteristic of electrolytes is shown by a graph.

Electric current in gases

In its normal state, the gaseous medium has insulating properties and does not conduct current. But under the influence of various perturbing factors, the dielectric characteristics can drop sharply and provoke the passage of ionization of the medium.

It arises from the bombardment of neutral atoms by moving electrons. As a result, one or more bound electrons are knocked out of the atom, and the atom receives a positive charge, turning into an ion. At the same time, inside the gas is formed additional quantity electrons that continue the ionization process.

Thus, inside the gas, an electric current is created by the simultaneous movement of positive and negative particles.

spark discharge

Upon heating or increasing the intensity of the applied electro magnetic field inside the gas, a spark first jumps. According to this principle, natural lightning is formed, which consists of channels, a flame and a discharge torch.

Under laboratory conditions, a spark jump can be observed between the electrodes of an electroscope. The practical implementation of a spark discharge in the spark plugs of internal combustion engines is known to every adult.

arc discharge

A spark is characterized by the fact that all the energy of the external field is immediately spent through it. If the voltage source is able to support the flow of current through the gas, then an arc occurs.

An example of an electric arc is the welding of metals different ways. For its flow, the emission of electrons from the cathode surface is used.

corona discharge

It occurs inside a gaseous medium with high intensities and non-uniform electromagnetic fields, which manifests itself on high-voltage overhead power lines with a voltage of 330 kV and above.

It flows between the wire and the closely spaced plane of the transmission line. During a corona discharge, ionization occurs by the method of electron impact near one of the electrodes, which has a region of increased tension.

glow discharge

It is used inside gases in special discharge gas-light lamps and tubes, voltage stabilizers. It is formed by lowering the pressure in the discharge gap.

When the ionization process in gases reaches a large value and they form equal number positive and negative charge carriers, then this state is called plasma. The glow discharge occurs in the plasma medium.

The current-voltage characteristic of the flow of currents in gases is shown in the picture. It consists of sections:

1. dependent;

2. self-discharge.

The first is characterized by what happens under the influence of an external ionizer and fades when it stops. And the independent discharge continues to flow under any condition.

Conductors with hole conductivity

These include:

germanium;

selenium;

silicon;

compounds of individual metals with tellurium, sulfur, selenium and some organic substances.

They are called semiconductors and belong to group No. 1, that is, they do not form the transfer of matter during the flow of charges. To increase the concentration of free electrons inside them, it is necessary to spend additional energy on detaching bound electrons. It is called ionization energy.

An electron-hole transition operates in the composition of a semiconductor. Due to its semiconductor passes current in one direction and blocks in the opposite direction when an opposite external field is applied to it.

Conductivity in semiconductors is:

1. own;

2. impurity.

The first type is inherent in structures in which charge carriers appear in the process of ionization of atoms of their substance: holes and electrons. Their concentration is mutually balanced.

The second type of semiconductors is created by including crystals with impurity conductivity. They possess atoms of a tri- or pentavalent element.

At very low temperatures Substances of certain categories of metals and alloys go into a state called superconductivity. For these substances, the electrical resistance to current decreases to almost zero.

The transition occurs due to a change in thermal properties. In relation to the absorption or release of heat during the transition to the superconducting state in the absence of a magnetic field, superconductors are divided into 2 types: No. 1 and No. 2.

The phenomenon of superconductivity of conductors occurs due to the formation of Cooper pairs, when a bound state is created for two neighboring electrons. The created pair has a double charge of the electron.

The distribution of electrons in a metal in a state of superconductivity is shown by a graph.

The magnetic induction of superconductors depends on the intensity of the electromagnetic field, and the magnitude of the latter is affected by the temperature of the substance.

The superconductivity properties of conductors are limited critical values limiting magnetic field and temperature for them.

Thus, conductors of electric current can be made of completely different substances and have different characteristics from each other. They are always affected by conditions. environment. For this reason, the boundaries performance characteristics conductors are always specified by technical standards.

When electricity appeared in our lives, few people knew about its properties and parameters, and they used various materials, it was noticeable that at the same value of the voltage of the current source on the consumer was different meaning voltage. It was clear that this was influenced by the type of material used as a conductor. When scientists took up the issue of studying this problem, they came to the conclusion that electrons are charge carriers in the material. And the ability to conduct electric current is isolated by the presence of free electrons in the material. It was found that some materials have a large number of these electrons, while others do not have them at all. Thus, there are materials that, and some do not have this ability.
Based on the above, all materials were divided into three groups:

• conductors;
• semiconductors;
• dielectrics;

Each of the groups has found wide application in electrical engineering.

conductors

guides are materials that conduct electricity well, they are used for the manufacture of wires, cable products, contact groups, windings, tires, conductive cores and tracks. Overwhelming majority electrical devices and devices is made on the basis of conductive materials. Moreover, I will say that the entire electric power industry could not exist without these substances. The group of conductors includes all metals, some liquids and gases.

It is also worth mentioning that among the conductors there are super conductors, the resistance of which is almost zero, such materials are very rare and expensive. And conductors with high resistance - tungsten, molybdenum, nichrome, etc. Such materials are used to make resistors, heating elements, and lamp coils.

But the lion's share in the electrical field belongs to ordinary conductors: copper, silver, aluminum, steel, various alloys of these metals. These materials have found the widest and greatest application in electrical engineering, especially copper and aluminum, since they are relatively cheap, and their use as conductors of electric current is most appropriate. Even copper is limited in its use, it is used as winding wires, multi-core cables, and more critical devices, copper busbars are even rarer. But aluminum is considered the king among the conductors of electric current, even if it has a higher resistivity than copper, but this is offset by its very low cost and corrosion resistance. It is widely used in power supply, cable products, overhead lines, busbars, conventional wires etc.

Semiconductors

Semiconductors, something between conductors and semiconductors. Their main feature is their dependence to conduct electric current from external conditions. The key condition is the presence of various impurities in the material, which just provide the ability to conduct electric current. Also, with a certain arrangement of two semiconductor materials. Based on these materials, this moment, many semiconductor devices have been produced: , LEDs, transistors,semistors, thyristors, stabistors, various microcircuits. There is a whole science devoted to semiconductors and devices based on them: electronic engineering. All computers, mobile devices. What can I say, almost all of our equipment contains semiconductor elements.

Semiconductor materials include: silicon, germanium, graphite, gr aphene, indium, etc.

Dielectrics

Well, the last group of materials is dielectrics Substances that are not capable of conducting electricity. Such materials include: wood, paper, air, oil, ceramics, glass, plastics, polyethylene, polyvinyl chloride, rubber, etc. Dielectrics are widely used due to their properties. They are used as an insulating material. They protect the contact of two current-carrying parts, do not allow a person to directly touch these parts. The role of a dielectric in electrical engineering is no less important than the role of conductors, as they ensure the stable, safe operation of all electrical and electronic devices. All dielectrics have a limit to which they are not able to conduct electric current, it is called breakdown voltage. This is an indicator at which the dielectric begins to pass an electric current, while heat is released and the dielectric itself is destroyed. This value of the breakdown voltage for each dielectric material is different and is given in reference materials. The higher it is, the better, the dielectric is considered more reliable.

The parameter characterizing the ability to conduct electric current is resistivity R , unit [ Ohm ] and conductivity, reciprocal of resistance. The higher this parameter, the worse the material conducts electric current. For conductors, it is from a few tenths to hundreds of ohms. In dielectrics, the resistance reaches tens of millions of ohms.

All three types of materials are widely used in the electric power industry and electrical engineering. They are also closely related to each other.

Substances through which electric charges are transmitted are called conductors of electricity.

Good conductors of electricity are metals, soil, solutions of salts, acids or alkalis in water, graphite. The human body also conducts electricity.

Of the metals, the best conductors of electricity are silver, copper and aluminum, so electrical network wires are most often made of copper or aluminum.

Substances through which charges are not transferred are called non-conductors (or insulators). Good insulators include ebonite, amber, porcelain, rubber, various, silk, kerosene, oils. Insulators (for example, the rubber sheath of a cable) are used to isolate wires through which current flows from external objects.

Questions

1. What substances are called conductors of electricity?
2. What substances are called insulators?
3. Name conductors and insulators of electricity.

Electrical circuit and its components

A battery (galvanic cell) can serve as a source of electric current.

At the power plant, electricity is generated by generators driven by steam and hydraulic turbines.

Electric motors, lamps, tiles powered by electric current are called receivers or consumers. Electrical energy is delivered to the receiver via wires.

Switches are used to turn electricity receivers on and off at the right time. The current source, receivers and switches, interconnected by wires, make up an electrical circuit.

In order for there to be current in the circuit, it must be closed, that is, it must consist only of conductors of electricity. If at any point the wire breaks, or an insulator is put in its place, the current in the target will stop. Such a circuit is called an open circuit.

Questions

1. What is the role of the current source in the circuit?
2. What are the parts of an electrical circuit?
3. What is a closed circuit? open?
4. What receivers or consumers do you know?

Electrical circuits

When you study geography, you use a plan and a map. Forests, villages, mountains and rivers are plotted on the plan and map with the help of conditional topographic signs.

In electrical engineering, a drawing card is also used. In such a drawing, the symbols depict the sources, receivers, switches, wires and products that make up the electrical circuit, as well as the connections between them. Such a drawing is called an electrical circuit.

Knowing conventions(see table below), it is easy to understand wiring diagram. If the same designations are repeated on the same diagram, then numbers are placed near the conventional signs, and the size, type and purpose are indicated in the plate attached to the diagram.

Questions

1. What is an electrical circuit?
2. What is shown on the electrical diagram?

Conventions constituent parts electrical circuit on the diagrams

Name	Symbol

"Plumbing", I.G. Spiridonov,
G.P. Bufetov, V.G. Kopelevich

Portable lighting or connecting cords of electrical household appliances are connected to a socket outlet using plugs. In the base of the insulating material of the socket, two brass sockets are fixed, to which wires from the electrical network are connected. Power socket The power plug consists of a body with a cord hole. The housing is made of insulating material and has metal bushings…

In industrial premises, in addition to switches, general circuit breakers are installed. V big houses Knife switches allow you to immediately turn off an entire section of the electrical network (for example, a floor or a group of apartments). At school, knife switches are installed in closed switchboards of training workshops, where they serve to turn on the electric motors of various machines. Breakers are: one-, two- and three-pole. Knife switches a - single-pole; b - bipolar; ...

It is often necessary to connect the wires of the electrical cord to the socket, switch, socket and to the clamps of electrical appliances. To do this, the ends of the wires to be connected are most often closed with a ring if they are put on bolts, sometimes with a poke when they are inserted into special bushings and fastened with screws. Termination of the ends of the wires a - ring; b - poke. When sealing with a ring, the ends of the wires ...

If the device does not work, then you should: by turning on a table or a special control lamp, check whether the socket is working; with a working socket, check by turning on the same lamp whether the cord of the device and the pins of the plug are not damaged. If plug socket and the plug, as well as the cord are in good condition, the device itself is damaged. The device may not work if it is burned out. a heating element or…

The main electrical quantities of an electrical circuit include current, voltage and resistance. Current strength Current strength refers to the electric charge passing through cross section wires per unit of time. Using the expressions "current strength", "strong current", "weak current", we must know what these expressions mean. The expression "strong current" means that a large ...

The term has two meanings: 1) an electrically conductive substance (for example, metal or electrolyte), 2) a part, product or structure that allows electricity to be transmitted.

The first value is used in physics and materials science, where all materials are divided into conductors, dielectrics and semiconductors according to their electrical conductivity. In power engineering, the second meaning of this term is more often used. Broadcast electrical energy it can occur along conductors - from one element of the source, converter or receiver of electrical energy to another along connecting conductors at a distance of several nanometers (for example, in integrated circuits) to several meters (for example, in powerful power equipment); - from one element of an electrical installation to another or from one electrical installation to another along electric lines at a distance of several meters (for example, within one installation) to several thousand kilometers (between large power systems).

The set of lines and their nodes in an electrical installation is called wiring, and the set of lines and their nodes, connecting electrical installations, - electrical network. By purpose and length in power systems, backbone (main) and distribution networks are distinguished, at enterprises, intershop and shop networks, etc.

The transfer of electric charge through a conductor (linen thread) was discovered in 1663 by the mayor of the city of Magdeburg, Otto von Guericke (1602–1686), who had previously manufactured the world's first electrostatic generator in the same year. A more detailed study of electrical phenomena began in the 18th century, and on July 2, 1729, the English amateur physicist Stephen Gray (Stephen Gray, 1666-1735) laid, using to test the transmission of electricity, an 80.5-foot-long hemp rope on horizontal silk cords (Fig. 4.5.1); with this he created the world's first electric line. On July 14, he held a public demonstration of the line, which was already 650 feet long, and the wire in which was still hemp rope laid along silk cords stretched between poles (the first overhead line). The experiment, despite the very poor conductivity of the wire, was surprisingly successful; the rope was obviously (thanks to the English climate) quite wet. Gray also introduced for the first time the classification of substances into conductive and non-conductive. Ten years later (in 1739) another English physicist Jean Theophile Desaguliers (1683–1744) introduced the concept of conductor. the first overhead line with metal (iron) wires was built in 1744 in Erfurt (Erfurt, Germany) by the German professor of philosophy Andreas Gordon (Andreas Gordon, 1712–1751), and the first experimental cable (telegraph) line was laid in 1841 in St. Petersburg by Boris Semenovich Jacobi (Moritz Hermann Jacobi).

Rice. 1. The principle of the device of the first electric line by Stephen Gray. 1 hemp rope (wire), 2 silk cords (insulators)

In electrical engineering, both flexible and rigid conductors are used. The first includes various wires and cables, to the second tires. Wires and busbars can be insulated or uninsulated (bare). Insulated wires and cables may contain from one to several current-carrying conductors isolated from each other.

hallmark cable is an airtight sheath made of polymer materials(for example, from polyvinyl chloride) or from metal (at present most often from aluminum, earlier mainly from lead), protecting the cores from harmful effects environment. A simplified classification of conductors according to their flexibility, insulation and application is shown in fig. 2.

Rice. 2. Classification of conductors (simplified)

The metal part of the cores, depending on the cross section and the required flexibility, can be massive or consist of wires; the diameter of the wires can in this case range from tenths of a millimeter (in fine-wire conductors) to several millimeters. Conductors are required

high electrical conductivity,
- good contact properties,
- high dielectric strength isolation,
- sufficient mechanical strength,
- sufficient flexibility (in case of wires and cables),
- long-term chemical stability,
- good resistance to heat
- sufficient heat capacity,
- protection from external influences,
- environmental friendliness,
- ease of use in electrical work,
- moderate cost.

Of the electrically conductive materials, these requirements are best met
- pure (without any impurities) copper,
- pure aluminum (for reasons of reliability, starting with a section of 16 mm2),
- in wires of overhead lines
- combinations of aluminum and steel.
The most commonly used insulating material
- polyethylene n,
- polyvinyl chloride n, which resists ignition better than other materials, but which contains toxic and environmentally hazardous chlorine, - synthetic (including especially heat-resistant organosilicon) rubbers.

Conductors (and cores of stranded conductors) are divided according to their purpose
- on the working conductors(to which, in the case alternating current include phase and neutral conductors; some networks or installations may not have neutral conductors);
- on the protective conductors necessary to ensure the safety of people;
- on the auxiliary conductors(for example, for control, communication or signaling). The working conductors may all be insulated from earth, but often one of them (usually the neutral) is earthed. Such a working grounding achieves a lower and evenly distributed voltage of the phase conductors relative to the ground, which, for example, in high voltage networks reduces the cost of insulation.

Protective conductors are provided for reliable grounding of those parts of electrical installations that, if the insulation is broken, may become energized (open conductive parts). Such protective earthing must prevent the occurrence of dangerous voltage between these parts and the earth, and thereby exclude the possibility of injury to people. electric shock. V electrical networks low voltage, it was previously practiced to combine the protective and neutral conductors; at present, these conductors, for reasons of reliability and safety, are separated from each other.