It is formed by the directed movement of free electrons and that in this case no changes in the substance from which the conductor is made do not occur.

Such conductors, in which the passage of an electric current is not accompanied by chemical changes in their substance, are called conductors of the first kind. These include all metals, coal and a number of other substances.

But there are also such conductors of electric current in nature, in which chemical phenomena occur during the passage of current. These conductors are called conductors of the second kind. These include mainly various solutions in water of acids, salts and alkalis.

If you pour water into a glass vessel and add a few drops of sulfuric acid (or some other acid or alkali) to it, and then take two metal plates and attach conductors to them by lowering these plates into the vessel, and connect a current source to the other ends of the conductors through a switch and an ammeter, then gas will be released from the solution, and it will continue continuously until the circuit is closed. acidified water is indeed a conductor. In addition, the plates will begin to be covered with gas bubbles. Then these bubbles will break away from the plates and come out.

When an electric current passes through the solution, chemical changes occur, as a result of which gas is released.

Conductors of the second kind are called electrolytes, and the phenomenon that occurs in the electrolyte when an electric current passes through it is.

Metal plates dipped into the electrolyte are called electrodes; one of them, connected to the positive pole of the current source, is called an anode, and the other, connected to the negative pole, is called cathode.

What causes the passage of electric current in a liquid conductor? It turns out that in such solutions (electrolytes), acid molecules (alkalis, salts) under the action of a solvent (in this case, water) decompose into two components, and one particle of the molecule has a positive electrical charge, and the other negative.

The particles of a molecule that have an electric charge are called ions. When an acid, salt or alkali is dissolved in water, a large number of both positive and negative ions appear in the solution.

Now it should become clear why an electric current passed through the solution, because between the electrodes connected to the current source, it was created, in other words, one of them turned out to be positively charged and the other negatively. Under the influence of this potential difference, positive ions began to move towards the negative electrode - the cathode, and negative ions - towards the anode.

Thus, the chaotic movement of ions has become an ordered counter-movement of negative ions in one direction and positive ones in the other. This charge transfer process constitutes the flow of electric current through the electrolyte and occurs as long as there is a potential difference across the electrodes. With the disappearance of the potential difference, the current through the electrolyte stops, the orderly movement of ions is disturbed, and chaotic movement sets in again.

As an example, consider the phenomenon of electrolysis when an electric current is passed through a solution of copper sulphate CuSO4 with copper electrodes lowered into it.

The phenomenon of electrolysis when current passes through a solution of copper sulphate: C - vessel with electrolyte, B - current source, C - switch

There will also be a counter movement of ions to the electrodes. The positive ion will be the copper (Cu) ion, and the negative ion will be the acid residue (SO4) ion. Copper ions, upon contact with the cathode, will be discharged (attaching the missing electrons to themselves), i.e., they will turn into neutral molecules of pure copper, and deposited on the cathode in the form of the thinnest (molecular) layer.

Negative ions, having reached the anode, are also discharged (give away excess electrons). But at the same time, they enter into a chemical reaction with the copper of the anode, as a result of which a molecule of copper Cu is attached to the acidic residue SO4 and a molecule of copper sulfate CuS O4 is formed, which is returned back to the electrolyte.

Since this chemical process takes a long time, copper is deposited on the cathode, which is released from the electrolyte. In this case, instead of the copper molecules that have gone to the cathode, the electrolyte receives new copper molecules due to the dissolution of the second electrode - the anode.

The same process occurs if zinc electrodes are taken instead of copper ones, and the electrolyte is a solution of zinc sulfate ZnSO4. Zinc will also be transferred from the anode to the cathode.

In this way, difference between electric current in metals and liquid conductors lies in the fact that in metals only free electrons, i.e., negative charges, are charge carriers, while in electrolytes it is carried by oppositely charged particles of matter - ions moving in opposite directions. Therefore they say that electrolytes have ionic conductivity.

The phenomenon of electrolysis was discovered in 1837 by B. S. Jacobi, who carried out numerous experiments on the study and improvement of chemical current sources. Jacobi found that one of the electrodes placed in a solution of copper sulphate, when an electric current passes through it, is covered with copper.

This phenomenon is called electroplating, finds extremely wide practical application now. One example of this is the coating of metal objects with a thin layer of other metals, i.e. nickel plating, gilding, silver plating, etc.

Gases (including air) do not conduct electricity under normal conditions. For example, naked, being suspended parallel to each other, are isolated from one another by a layer of air.

However, under the influence of high temperature, a large potential difference, and other reasons, gases, like liquid conductors, ionize, i.e., particles of gas molecules appear in them in large numbers, which, being carriers of electricity, contribute to the passage of electric current through the gas.

But at the same time, the ionization of a gas differs from the ionization of a liquid conductor. If in a liquid a molecule breaks up into two charged parts, then in gases, under the action of ionization, electrons are always separated from each molecule and an ion remains in the form of a positively charged part of the molecule.

One has only to stop the ionization of the gas, as it ceases to be conductive, while the liquid always remains a conductor of electric current. Consequently, the conductivity of a gas is a temporary phenomenon, depending on the action of external factors.

However, there is another one called arc discharge or just an electric arc. The phenomenon of an electric arc was discovered at the beginning of the 19th century by the first Russian electrical engineer V. V. Petrov.

V. V. Petrov, doing numerous experiments, discovered that between two charcoal connected to a current source, a continuous electric discharge occurs through the air, accompanied by a bright light. In his writings, V. V. Petrov wrote that in this case, "the dark peace can be brightly enough illuminated." So for the first time electric light was obtained, which was practically applied by another Russian electrical scientist Pavel Nikolaevich Yablochkov.

"Yablochkov's Candle", whose work is based on the use of an electric arc, made a real revolution in electrical engineering in those days.

The arc discharge is used as a source of light even today, for example, in searchlights and projectors. The high temperature of the arc discharge allows it to be used for . At present, arc furnaces powered by a very high current are used in a number of industries: for the smelting of steel, cast iron, ferroalloys, bronze, etc. And in 1882, N. N. Benardos first used an arc discharge for cutting and welding metal.

In gas-light tubes, fluorescent lamps, voltage stabilizers, to obtain electron and ion beams, the so-called glow gas discharge.

A spark discharge is used to measure large potential differences using a spherical spark gap, the electrodes of which are two metal balls with a polished surface. The balls are moved apart, and a measured potential difference is applied to them. Then the balls are brought together until a spark jumps between them. Knowing the diameter of the balls, the distance between them, the pressure, temperature and humidity of the air, they find the potential difference between the balls according to special tables. This method can be used to measure, to within a few percent, potential differences of the order of tens of thousands of volts.

There are no absolute dielectrics in nature. The ordered movement of particles - carriers of electric charge - that is, current, can be caused in any medium, but this requires special conditions. We will consider here how electrical phenomena proceed in gases and how a gas can be changed from a very good dielectric into a very good conductor. We will be interested in the conditions under which it arises, and also in what features the electric current in gases is characterized.

Electrical properties of gases

A dielectric is a substance (medium) in which the concentration of particles - free carriers of an electric charge - does not reach any significant value, as a result of which the conductivity is negligible. All gases are good dielectrics. Their insulating properties are used everywhere. For example, in any circuit breaker, the opening of the circuit occurs when the contacts are brought into such a position that an air gap forms between them. Wires in power lines are also isolated from each other by an air layer.

The structural unit of any gas is a molecule. It consists of atomic nuclei and electron clouds, that is, it is a collection of electric charges distributed in space in some way. A gas molecule can be due to the peculiarities of its structure or be polarized under the action of an external electric field. The vast majority of the molecules that make up a gas are electrically neutral under normal conditions, since the charges in them cancel each other out.

If an electric field is applied to the gas, the molecules will assume a dipole orientation, occupying a spatial position that compensates for the effect of the field. The charged particles present in the gas under the influence of Coulomb forces will begin to move: positive ions - in the direction of the cathode, negative ions and electrons - towards the anode. However, if the field has insufficient potential, a single directed flow of charges does not arise, and one can rather speak of separate currents, so weak that they should be neglected. The gas behaves like a dielectric.

Thus, for the occurrence of an electric current in gases, a high concentration of free charge carriers and the presence of a field are required.

Ionization

The process of an avalanche-like increase in the number of free charges in a gas is called ionization. Accordingly, a gas in which there is a significant amount of charged particles is called ionized. It is in such gases that an electric current is created.

The ionization process is associated with a violation of the neutrality of molecules. As a result of the detachment of an electron, positive ions appear, the attachment of an electron to a molecule leads to the formation of a negative ion. In addition, there are many free electrons in an ionized gas. Positive ions and especially electrons are the main charge carriers for electric current in gases.

Ionization occurs when a certain amount of energy is imparted to a particle. Thus, an external electron in the composition of a molecule, having received this energy, can leave the molecule. Mutual collisions of charged particles with neutral ones lead to the knocking out of new electrons, and the process takes on an avalanche-like character. The kinetic energy of the particles also increases, which greatly promotes ionization.

Where does the energy expended on the excitation of electric current in gases come from? Ionization of gases has several sources of energy, according to which it is customary to name its types.

1. Ionization by an electric field. In this case, the potential energy of the field is converted into the kinetic energy of the particles.
2. Thermal ionization. An increase in temperature also leads to the formation of a large number of free charges.
3. Photoionization. The essence of this process is that the electrons are supplied with energy by electromagnetic radiation quanta - photons, if they have a sufficiently high frequency (ultraviolet, x-ray, gamma quanta).
4. Impact ionization is the result of the conversion of the kinetic energy of colliding particles into the energy of electron detachment. Along with thermal ionization, it serves as the main factor in the excitation of electric current in gases.

Each gas is characterized by a certain threshold value - the ionization energy necessary for an electron to break away from a molecule, overcoming a potential barrier. This value for the first electron ranges from several volts to two tens of volts; more energy is needed to detach the next electron from the molecule, and so on.

It should be taken into account that simultaneously with ionization in the gas, the reverse process occurs - recombination, that is, the restoration of neutral molecules under the action of the Coulomb forces of attraction.

Gas discharge and its types

So, the electric current in gases is due to the ordered movement of charged particles under the action of an electric field applied to them. The presence of such charges, in turn, is possible due to various ionization factors.

Thus, thermal ionization requires significant temperatures, but an open flame in connection with some chemical processes contributes to ionization. Even at a relatively low temperature in the presence of a flame, the appearance of an electric current in gases is recorded, and experiment with gas conductivity makes it easy to verify this. It is necessary to place the flame of a burner or candle between the plates of a charged capacitor. The circuit previously open due to the air gap in the capacitor will close. A galvanometer connected to the circuit will show the presence of current.

Electric current in gases is called a gas discharge. It must be borne in mind that in order to maintain the stability of the discharge, the action of the ionizer must be constant, since due to constant recombination, the gas loses its electrically conductive properties. Some carriers of electric current in gases - ions - are neutralized on the electrodes, others - electrons - getting to the anode, are sent to the "plus" of the field source. If the ionizing factor ceases to operate, the gas will immediately become a dielectric again, and the current will cease. Such a current, dependent on the action of an external ionizer, is called a non-self-sustaining discharge.

Features of the passage of electric current through gases are described by a special dependence of the current strength on voltage - the current-voltage characteristic.

Let us consider the development of a gas discharge on the graph of the current-voltage dependence. When the voltage rises to a certain value U 1, the current increases in proportion to it, that is, Ohm's law is fulfilled. The kinetic energy increases, and hence the velocity of charges in the gas, and this process is ahead of recombination. At voltage values ​​from U 1 to U 2, this relationship is violated; when U 2 is reached, all charge carriers reach the electrodes without having time to recombine. All free charges are involved, and a further increase in voltage does not lead to an increase in current. This nature of the movement of charges is called saturation current. Thus, we can say that the electric current in gases is also due to the peculiarities of the behavior of an ionized gas in electric fields of various strengths.

When the potential difference across the electrodes reaches a certain value U 3 , the voltage becomes sufficient for the electric field to cause an avalanche-like ionization of the gas. The kinetic energy of free electrons is already enough for impact ionization of molecules. At the same time, their speed in most gases is about 2000 km / s and higher (it is calculated by the approximate formula v=600 U i , where U i is the ionization potential). At this moment, a gas breakdown occurs and a significant increase in current occurs due to an internal ionization source. Therefore, such a discharge is called independent.

The presence of an external ionizer in this case no longer plays a role in maintaining an electric current in the gases. A self-sustained discharge under different conditions and with different characteristics of the source of the electric field can have certain features. There are such types of self-discharge as glow, spark, arc and corona. We will look at how electric current behaves in gases, briefly for each of these types.

A potential difference from 100 (and even less) to 1000 volts is enough to initiate a self-discharge. Therefore, a glow discharge, characterized by a low current strength (from 10 -5 A to 1 A), occurs at pressures of no more than a few millimeters of mercury.

In a tube with a rarefied gas and cold electrodes, the emerging glow discharge looks like a thin luminous cord between the electrodes. If we continue pumping the gas out of the tube, the filament will be washed out, and at pressures of tenths of millimeters of mercury, the glow fills the tube almost completely. The glow is absent near the cathode - in the so-called dark cathode space. The rest is called the positive column. In this case, the main processes that ensure the existence of the discharge are localized precisely in the dark cathode space and in the region adjacent to it. Here, charged gas particles are accelerated, knocking out electrons from the cathode.

In a glow discharge, the cause of ionization is electron emission from the cathode. The electrons emitted by the cathode produce impact ionization of gas molecules, the emerging positive ions cause secondary emission from the cathode, and so on. The glow of the positive column is mainly due to the recoil of photons by excited gas molecules, and different gases are characterized by the glow of a certain color. The positive column takes part in the formation of a glow discharge only as a section of the electrical circuit. If you bring the electrodes closer together, you can achieve the disappearance of the positive column, but the discharge will not stop. However, with a further reduction in the distance between the electrodes, the glow discharge cannot exist.

It should be noted that for this type of electric current in gases, the physics of some processes has not yet been fully elucidated. For example, the nature of the forces causing an increase in the current to expand the area on the cathode surface that takes part in the discharge remains unclear.

spark discharge

Spark breakdown has a pulsed character. It occurs at pressures close to normal atmospheric, in cases where the power of the electric field source is not enough to maintain a stationary discharge. In this case, the field strength is high and can reach 3 MV/m. The phenomenon is characterized by a sharp increase in the discharge electric current in the gas, at the same time the voltage drops extremely quickly, and the discharge stops. Then the potential difference increases again, and the whole process is repeated.

With this type of discharge, short-term spark channels are formed, the growth of which can begin from any point between the electrodes. This is due to the fact that impact ionization occurs randomly in places where the greatest number of ions is currently concentrated. Near the spark channel, the gas heats up rapidly and undergoes thermal expansion, which causes acoustic waves. Therefore, the spark discharge is accompanied by crackling, as well as the release of heat and a bright glow. Avalanche ionization processes generate high pressures and temperatures up to 10,000 degrees and more in the spark channel.

The most striking example of a natural spark discharge is lightning. The diameter of the main lightning spark channel can range from a few centimeters to 4 m, and the channel length can reach 10 km. The magnitude of the current reaches 500 thousand amperes, and the potential difference between a thundercloud and the Earth's surface reaches a billion volts.

The longest lightning with a length of 321 km was observed in 2007 in Oklahoma, USA. The record holder for the duration was lightning, recorded in 2012 in the French Alps - it lasted over 7.7 seconds. When struck by lightning, the air can heat up to 30 thousand degrees, which is 6 times higher than the temperature of the visible surface of the Sun.

In cases where the power of the source of the electric field is large enough, the spark discharge develops into an arc discharge.

This type of self-sustained discharge is characterized by high current density and low (less than glow discharge) voltage. The breakdown distance is small due to the proximity of the electrodes. The discharge is initiated by the emission of an electron from the cathode surface (for metal atoms, the ionization potential is small compared to gas molecules). During a breakdown between the electrodes, conditions are created under which the gas conducts an electric current, and a spark discharge occurs, which closes the circuit. If the power of the voltage source is large enough, spark discharges turn into a stable electric arc.

Ionization during an arc discharge reaches almost 100%, the current strength is very high and can range from 10 to 100 amperes. At atmospheric pressure, the arc is capable of heating up to 5-6 thousand degrees, and the cathode - up to 3 thousand degrees, which leads to intense thermionic emission from its surface. The bombardment of the anode with electrons leads to partial destruction: a recess is formed on it - a crater with a temperature of about 4000 ° C. An increase in pressure causes an even greater increase in temperature.

When diluting the electrodes, the arc discharge remains stable up to a certain distance, which makes it possible to deal with it in those parts of electrical equipment where it is harmful due to the corrosion and burnout of contacts caused by it. These are devices such as high-voltage and automatic switches, contactors and others. One of the methods to combat the arc that occurs when the contacts open is the use of arc chutes based on the principle of arc extension. Many other methods are also used: shunting contacts, using materials with a high ionization potential, and so on.

The development of a corona discharge occurs at normal atmospheric pressure in sharply inhomogeneous fields near electrodes with a large curvature of the surface. These can be spiers, masts, wires, various elements of electrical equipment that have a complex shape, and even human hair. Such an electrode is called a corona electrode. Ionization processes and, accordingly, the glow of the gas take place only near it.

The corona can be formed both on the cathode (negative corona) when it is bombarded with ions, and on the anode (positive) as a result of photoionization. The negative corona, in which the ionization process is directed away from the electrode as a result of thermal emission, is characterized by an even glow. In the positive corona, streamers can be observed - luminous lines of a broken configuration that can turn into spark channels.

An example of a corona discharge in natural conditions are those that occur on the tips of high masts, treetops, and so on. They are formed at a high electric field strength in the atmosphere, often before a thunderstorm or during a snowstorm. In addition, they were fixed on the skin of aircraft that fell into a cloud of volcanic ash.

Corona discharge on the wires of power lines leads to significant losses of electricity. At a high voltage, a corona discharge can turn into an arc. It is fought in various ways, for example, by increasing the radius of curvature of the conductors.

Electric current in gases and plasma

A fully or partially ionized gas is called plasma and is considered the fourth state of matter. On the whole, plasma is electrically neutral, since the total charge of its constituent particles is zero. This distinguishes it from other systems of charged particles, such as, for example, electron beams.

Under natural conditions, plasma is formed, as a rule, at high temperatures due to the collision of gas atoms at high speeds. The vast majority of baryonic matter in the Universe is in the state of plasma. These are stars, part of interstellar matter, intergalactic gas. The earth's ionosphere is also a rarefied, weakly ionized plasma.

The degree of ionization is an important characteristic of a plasma; its conductive properties depend on it. The degree of ionization is defined as the ratio of the number of ionized atoms to the total number of atoms per unit volume. The more ionized the plasma, the higher its electrical conductivity. In addition, it has high mobility.

We see, therefore, that the gases that conduct electricity within the discharge channel are nothing but plasma. Thus, glow and corona discharges are examples of cold plasma; a lightning spark channel or an electric arc are examples of a hot, almost completely ionized plasma.

Electric current in metals, liquids and gases - differences and similarities

Let us consider the features that characterize the gas discharge in comparison with the properties of the current in other media.

In metals, current is the directed movement of free electrons that does not entail chemical changes. Conductors of this type are called conductors of the first kind; these include, in addition to metals and alloys, coal, some salts and oxides. They are distinguished by electronic conductivity.

Conductors of the second kind are electrolytes, that is, liquid aqueous solutions of alkalis, acids and salts. The passage of current is associated with a chemical change in the electrolyte - electrolysis. Ions of a substance dissolved in water, under the action of a potential difference, move in opposite directions: positive cations - to the cathode, negative anions - to the anode. The process is accompanied by gas evolution or deposition of a metal layer on the cathode. Conductors of the second kind are characterized by ionic conductivity.

As for the conductivity of gases, it is, firstly, temporary, and secondly, it has signs of similarity and difference with each of them. So, the electric current in both electrolytes and gases is a drift of oppositely charged particles directed towards opposite electrodes. However, while electrolytes are characterized by purely ionic conductivity, in a gas discharge with a combination of electronic and ionic types of conductivity, the leading role belongs to electrons. Another difference between the electric current in liquids and gases is the nature of ionization. In an electrolyte, the molecules of a dissolved compound dissociate in water, but in a gas, the molecules do not break down, but only lose electrons. Therefore, the gas discharge, like the current in metals, is not associated with chemical changes.

The current in liquids and gases is also not the same. The conductivity of electrolytes as a whole obeys Ohm's law, but it is not observed during a gas discharge. The volt-ampere characteristic of gases has a much more complex character associated with the properties of the plasma.

Mention should also be made of the general and distinctive features of the electric current in gases and in vacuum. Vacuum is an almost perfect dielectric. "Almost" - because in vacuum, despite the absence (more precisely, an extremely low concentration) of free charge carriers, a current is also possible. But potential carriers are already present in the gas, they only need to be ionized. Charge carriers are brought into vacuum from matter. As a rule, this occurs in the process of electron emission, for example, when the cathode is heated (thermionic emission). But, as we have seen, emission also plays an important role in various types of gas discharges.

The use of gas discharges in technology

The harmful effects of certain discharges have already been briefly discussed above. Now let's pay attention to the benefits that they bring in industry and in everyday life.

Glow discharge is used in electrical engineering (voltage stabilizers), in coating technology (cathode sputtering method based on the phenomenon of cathode corrosion). In electronics, it is used to produce ion and electron beams. A well-known area of ​​application for glow discharges are fluorescent and so-called economical lamps and decorative neon and argon discharge tubes. In addition, the glow discharge is used in and in spectroscopy.

Spark discharge is used in fuses, in electroerosive methods of precision metal processing (spark cutting, drilling, and so on). But it is best known for the use of internal combustion engines in spark plugs and household appliances (gas stoves).

The arc discharge, being first used in lighting technology as early as 1876 (Yablochkov's candle - "Russian light"), still serves as a light source - for example, in projectors and powerful spotlights. In electrical engineering, the arc is used in mercury rectifiers. In addition, it is used in electric welding, metal cutting, industrial electric furnaces for steel and alloy smelting.

Corona discharge finds application in electrostatic precipitators for ion gas purification, in elementary particle counters, in lightning rods, in air conditioning systems. Corona discharge also works in copiers and laser printers, where it charges and discharges a photosensitive drum and transfers powder from the drum to paper.

Thus, gas discharges of all types are widely used. Electric current in gases is successfully and effectively used in many areas of technology.

Topics of the USE codifier: carriers of free electric charges in gases.

Under ordinary conditions, gases consist of electrically neutral atoms or molecules; There are almost no free charges in gases. Therefore gases are dielectrics- electric current does not pass through them.

We said "almost none" because in fact, in gases and, in particular, in the air, there is always a certain amount of free charged particles. They appear as a result of the ionizing effect of radiation from radioactive substances that make up the earth's crust, ultraviolet and x-ray radiation from the sun, as well as cosmic rays - streams of high-energy particles penetrating the earth's atmosphere from outer space. Later we will return to this fact and discuss its importance, but for now we will only note that under normal conditions the conductivity of gases, caused by the “natural” amount of free charges, is negligible and can be ignored.

The action of switches in electrical circuits is based on the insulating properties of the air gap ( fig. 1). For example, a small air gap in a light switch is enough to open an electrical circuit in your room.

Rice. 1 key

It is possible, however, to create such conditions under which an electric current will appear in the gas gap. Let's consider the following experience.

We charge the plates of the air capacitor and connect them to a sensitive galvanometer (Fig. 2, left). At room temperature and not too humid air, the galvanometer will not show a noticeable current: our air gap, as we said, is not a conductor of electricity.

Rice. 2. The occurrence of current in the air

Now let's bring the flame of a burner or a candle into the gap between the plates of the capacitor (Fig. 2, on the right). Current appears! Why?

Free charges in a gas

The occurrence of an electric current between the plates of the condenser means that in the air under the influence of the flame appeared free charges. What exactly?

Experience shows that electric current in gases is an ordered movement of charged particles. three types. it electrons, positive ions and negative ions.

Let's see how these charges can appear in a gas.

As the gas temperature increases, the thermal vibrations of its particles - molecules or atoms - become more intense. The impacts of particles against each other reach such a force that ionization- decay of neutral particles into electrons and positive ions (Fig. 3).

Rice. 3. Ionization

Degree of ionization is the ratio of the number of decayed gas particles to the total initial number of particles. For example, if the degree of ionization is , then this means that the original gas particles have decayed into positive ions and electrons.

The degree of gas ionization depends on temperature and increases sharply with its increase. For hydrogen, for example, at a temperature below the degree of ionization does not exceed , and at a temperature above the degree of ionization is close to (that is, hydrogen is almost completely ionized (partially or completely ionized gas is called plasma)).

In addition to high temperature, there are other factors that cause gas ionization.

We have already mentioned them in passing: these are radioactive radiation, ultraviolet, X-ray and gamma rays, cosmic particles. Any such factor that causes the ionization of a gas is called ionizer.

Thus, ionization does not occur by itself, but under the influence of an ionizer.

At the same time, the reverse process recombination, that is, the reunion of an electron and a positive ion into a neutral particle (Fig. 4).

Rice. 4. Recombination

The reason for recombination is simple: it is the Coulomb attraction of oppositely charged electrons and ions. Rushing towards each other under the action of electrical forces, they meet and get the opportunity to form a neutral atom (or molecule - depending on the type of gas).

At a constant intensity of the ionizer action, a dynamic equilibrium is established: the average number of particles decaying per unit time is equal to the average number of recombining particles (in other words, the ionization rate is equal to the recombination rate). If the ionizer action is strengthened (for example, the temperature is increased), then the dynamic equilibrium will shift to direction of ionization, and the concentration of charged particles in the gas will increase. On the contrary, if you turn off the ionizer, then recombination will begin to prevail, and free charges will gradually disappear completely.

So, positive ions and electrons appear in the gas as a result of ionization. Where does the third kind of charges come from - negative ions? Very simple: an electron can fly into a neutral atom and join it! This process is shown in Fig. 5 .

Rice. 5. The appearance of a negative ion

The negative ions formed in this way will participate in the creation of the current along with positive ions and electrons.

Non-self discharge

If there is no external electric field, then free charges perform chaotic thermal motion along with neutral gas particles. But when an electric field is applied, the ordered movement of charged particles begins - electric current in gas.

Rice. 6. Non-self-sustained discharge

On fig. 6 we see three types of charged particles arising in the gas gap under the action of an ionizer: positive ions, negative ions and electrons. An electric current in a gas is formed as a result of the oncoming movement of charged particles: positive ions - to the negative electrode (cathode), electrons and negative ions - to the positive electrode (anode).

Electrons, falling on the positive anode, are sent along the circuit to the "plus" of the current source. Negative ions donate an extra electron to the anode and, having become neutral particles, return to the gas; the electron given to the anode also rushes to the “plus” of the source. Positive ions, coming to the cathode, take electrons from there; the resulting shortage of electrons at the cathode is immediately compensated by their delivery there from the “minus” of the source. As a result of these processes, an ordered movement of electrons occurs in the external circuit. This is the electric current recorded by the galvanometer.

The process described in Fig. 6 is called non-self-sustained discharge in gas. Why dependent? Therefore, to maintain it, the constant action of the ionizer is necessary. Let's remove the ionizer - and the current will stop, since the mechanism that ensures the appearance of free charges in the gas gap will disappear. The space between the anode and cathode will again become an insulator.

Volt-ampere characteristic of gas discharge

The dependence of the current strength through the gas gap on the voltage between the anode and cathode (the so-called current-voltage characteristic of gas discharge) is shown in Fig. 7.

Rice. 7. Volt-ampere characteristic of gas discharge

At zero voltage, the current strength, of course, is equal to zero: charged particles perform only thermal movement, there is no ordered movement between the electrodes.

With a small voltage, the current strength is also small. The fact is that not all charged particles are destined to get to the electrodes: some of the positive ions and electrons in the process of their movement find each other and recombine.

As the voltage increases, free charges develop more and more speed, and the less chance a positive ion and an electron have to meet and recombine. Therefore, an increasing part of the charged particles reaches the electrodes, and the current strength increases (section ).

At a certain voltage value (point ), the charge velocity becomes so high that recombination does not have time to occur at all. From now on all charged particles formed under the action of the ionizer reach the electrodes, and current reaches saturation- Namely, the current strength ceases to change with increasing voltage. This will continue up to a certain point.

self-discharge

After passing the point, the current strength increases sharply with increasing voltage - begins independent discharge. Now we will figure out what it is.

Charged gas particles move from collision to collision; in the intervals between collisions, they are accelerated by an electric field, increasing their kinetic energy. And now, when the voltage becomes large enough (that same point), the electrons during their free path reach such energies that when they collide with neutral atoms, they ionize them! (Using the laws of conservation of momentum and energy, it can be shown that it is electrons (and not ions) accelerated by an electric field that have the maximum ability to ionize atoms.)

The so-called electron impact ionization. Electrons knocked out of ionized atoms are also accelerated by the electric field and hit new atoms, ionizing them now and generating new electrons. As a result of the emerging electron avalanche, the number of ionized atoms rapidly increases, as a result of which the current strength also increases rapidly.

The number of free charges becomes so large that the need for an external ionizer is eliminated. It can be simply removed. Free charged particles are now spawned as a result of internal processes occurring in the gas - that's why the discharge is called independent.

If the gas gap is under high voltage, then no ionizer is needed for self-discharge. It is enough to find only one free electron in the gas, and the above-described electron avalanche will begin. And there will always be at least one free electron!

Let us recall once again that in a gas, even under normal conditions, there is a certain “natural” amount of free charges, due to the ionizing radioactive radiation of the earth's crust, high-frequency radiation from the Sun, and cosmic rays. We have seen that at low voltages the conductivity of the gas caused by these free charges is negligible, but now - at a high voltage - they will give rise to an avalanche of new particles, giving rise to an independent discharge. It will happen as they say breakdown gas gap.

The field strength required to break down dry air is approximately kV/cm. In other words, in order for a spark to jump between the electrodes separated by a centimeter of air, a kilovolt voltage must be applied to them. Imagine what voltage is needed to break through several kilometers of air! But it is precisely such breakdowns that occur during a thunderstorm - these are lightning well known to you.

Under normal conditions, gases are dielectrics, because. consist of neutral atoms and molecules, and they do not have a sufficient number of free charges. Gases become conductors only when they are somehow ionized. The process of ionization of gases consists in the fact that under the influence of any reasons one or more electrons are detached from the atom. As a result, instead of a neutral atom, positive ion and electron.

The breakdown of molecules into ions and electrons is called gas ionization.

Part of the formed electrons can be captured by other neutral atoms, and then appear negatively charged ions.

Thus, there are three types of charge carriers in an ionized gas: electrons, positive ions, and negative ones.

The separation of an electron from an atom requires the expenditure of a certain energy - ionization energy W i . The ionization energy depends on the chemical nature of the gas and the energy state of the electron in the atom. So, for the detachment of the first electron from the nitrogen atom, an energy of 14.5 eV is spent, and for the detachment of the second electron - 29.5 eV, for the detachment of the third - 47.4 eV.

The factors that cause gas ionization are called ionizers.

There are three types of ionization: thermal ionization, photoionization and impact ionization.

Thermal ionization occurs as a result of a collision of atoms or molecules of a gas at high temperature, if the kinetic energy of the relative motion of the colliding particles exceeds the binding energy of an electron in an atom.

Photoionization occurs under the influence of electromagnetic radiation (ultraviolet, x-ray or γ-radiation), when the energy necessary to detach an electron from an atom is transferred to it by a radiation quantum.

Ionization by electron impact(or impact ionization) is the formation of positively charged ions as a result of collisions of atoms or molecules with fast electrons with high kinetic energy.

The process of gas ionization is always accompanied by the opposite process of recovery of neutral molecules from oppositely charged ions due to their electrical attraction. This phenomenon is called recombination. During recombination, energy is released equal to the energy spent on ionization. This can cause, for example, gas glow.

If the action of the ionizer is unchanged, then dynamic equilibrium is established in the ionized gas, in which as many molecules are restored per unit time as they decay into ions. In this case, the concentration of charged particles in the ionized gas remains unchanged. If, however, the action of the ionizer is stopped, then recombination will begin to prevail over ionization, and the number of ions will rapidly decrease to almost zero. Consequently, the presence of charged particles in a gas is a temporary phenomenon (as long as the ionizer is in operation).

In the absence of an external field, charged particles move randomly.

gas discharge

When an ionized gas is placed in an electric field, electric forces begin to act on free charges, and they drift parallel to the lines of tension: electrons and negative ions - to the anode, positive ions - to the cathode (Fig. 1). At the electrodes, ions turn into neutral atoms by donating or accepting electrons, thereby completing the circuit. An electric current is generated in the gas.

Electric current in gases is the directed movement of ions and electrons.

Electric current in gases is called gas discharge.

The total current in the gas is composed of two streams of charged particles: the stream going to the cathode and the stream directed to the anode.

In gases, electronic conductivity, similar to the conductivity of metals, is combined with ionic conductivity, similar to the conductivity of aqueous solutions or electrolyte melts.

Thus, the conductivity of gases has ion-electronic character.

Physics abstract

on the topic:

"Electric current in gases".

Electric current in gases.

1. Electric discharge in gases.

All gases in their natural state do not conduct electricity. This can be seen from the following experience:

Let's take an electrometer with disks of a flat capacitor attached to it and charge it. At room temperature, if the air is dry enough, the capacitor does not noticeably discharge - the position of the electrometer needle does not change. It takes a long time to notice a decrease in the angle of deflection of the electrometer needle. This shows that the electric current in the air between the disks is very small. This experience shows that air is a poor conductor of electric current.

Let's modify the experiment: let's heat the air between the discs with the flame of an alcohol lamp. Then the angle of deflection of the electrometer pointer rapidly decreases, i.e. the potential difference between the disks of the capacitor decreases - the capacitor is discharged. Consequently, the heated air between the discs has become a conductor, and an electric current is established in it.

The insulating properties of gases are explained by the fact that there are no free electric charges in them: the atoms and molecules of gases in their natural state are neutral.

2. Ionization of gases.

The above experience shows that charged particles appear in gases under the influence of high temperature. They arise as a result of the splitting off of one or more electrons from gas atoms, as a result of which a positive ion and electrons appear instead of a neutral atom. Part of the formed electrons can be captured by other neutral atoms, and then more negative ions will appear. The breakdown of gas molecules into electrons and positive ions is called ionization of gases.

Heating a gas to a high temperature is not the only way to ionize gas molecules or atoms. Gas ionization can occur under the influence of various external interactions: strong heating of the gas, x-rays, a-, b- and g-rays arising from radioactive decay, cosmic rays, bombardment of gas molecules by fast moving electrons or ions. The factors that cause gas ionization are called ionizers. The quantitative characteristic of the ionization process is ionization intensity, measured by the number of pairs of charged particles opposite in sign that appear in a unit volume of gas per unit time.

The ionization of an atom requires the expenditure of a certain energy - the ionization energy. To ionize an atom (or molecule), it is necessary to do work against the forces of interaction between the ejected electron and the rest of the particles of the atom (or molecule). This work is called the work of ionization A i . The value of the work of ionization depends on the chemical nature of the gas and the energy state of the ejected electron in the atom or molecule.

After the termination of the ionizer, the number of ions in the gas decreases over time and eventually the ions disappear altogether. The disappearance of ions is explained by the fact that ions and electrons participate in thermal motion and therefore collide with each other. When a positive ion and an electron collide, they can reunite into a neutral atom. In the same way, when a positive and negative ion collides, the negative ion can give up its excess electron to the positive ion and both ions will turn into neutral atoms. This process of mutual neutralization of ions is called ion recombination. When a positive ion and an electron or two ions recombine, a certain energy is released, equal to the energy spent on ionization. Partially, it is emitted in the form of light, and therefore the recombination of ions is accompanied by luminescence (luminescence of recombination).

In the phenomena of electric discharge in gases, the ionization of atoms by electron impacts plays an important role. This process consists in the fact that a moving electron with sufficient kinetic energy knocks out one or more atomic electrons from it when it collides with a neutral atom, as a result of which the neutral atom turns into a positive ion, and new electrons appear in the gas (this will be discussed later).

The table below gives the ionization energies of some atoms.

3. Mechanism of electrical conductivity of gases.

The mechanism of gas conductivity is similar to the mechanism of conductivity of electrolyte solutions and melts. In the absence of an external field, charged particles, like neutral molecules, move randomly. If ions and free electrons find themselves in an external electric field, then they come into directed motion and create an electric current in gases.

Thus, the electric current in the gas is a directed movement of positive ions to the cathode, and negative ions and electrons to the anode. The total current in the gas is composed of two streams of charged particles: the stream going to the anode and the stream directed to the cathode.

Neutralization of charged particles occurs on the electrodes, as in the case of the passage of electric current through solutions and melts of electrolytes. However, in gases there is no release of substances on the electrodes, as is the case in electrolyte solutions. Gas ions, approaching the electrodes, give them their charges, turn into neutral molecules and diffuse back into the gas.

Another difference in the electrical conductivity of ionized gases and solutions (melts) of electrolytes is that the negative charge during the passage of current through gases is transferred mainly not by negative ions, but by electrons, although conductivity due to negative ions can also play a certain role.

Thus, gases combine electronic conductivity, similar to the conductivity of metals, with ionic conductivity, similar to the conductivity of aqueous solutions and electrolyte melts.

4. Non-self-sustained gas discharge.

The process of passing an electric current through a gas is called a gas discharge. If the electrical conductivity of the gas is created by external ionizers, then the electric current arising in it is called non-self-sustaining gas discharge. With the termination of the action of external ionizers, the non-self-sustained discharge ceases. A non-self-sustaining gas discharge is not accompanied by gas glow.

Below is a graph of the dependence of the current strength on the voltage for a non-self-sustained discharge in a gas. A glass tube with two metal electrodes soldered into the glass was used to plot the graph. The chain is assembled as shown in the figure below.

At a certain voltage, there comes a point at which all the charged particles formed in the gas by the ionizer in a second reach the electrodes in the same time. A further increase in voltage can no longer lead to an increase in the number of transported ions. The current reaches saturation (horizontal section of graph 1).

5. Independent gas discharge.

An electric discharge in a gas that persists after the termination of the action of an external ionizer is called independent gas discharge. For its implementation, it is necessary that as a result of the discharge itself, free charges are continuously formed in the gas. The main source of their occurrence is the impact ionization of gas molecules.

If, after reaching saturation, we continue to increase the potential difference between the electrodes, then the current strength at a sufficiently high voltage will increase sharply (graph 2).

This means that additional ions appear in the gas, which are formed due to the action of the ionizer. The current strength can increase hundreds and thousands of times, and the number of charged particles that appear during the discharge can become so large that an external ionizer is no longer needed to maintain the discharge. Therefore, the ionizer can now be removed.

What are the reasons for the sharp increase in current strength at high voltages? Let us consider any pair of charged particles (a positive ion and an electron) formed due to the action of an external ionizer. The free electron that appears in this way begins to move towards the positive electrode - the anode, and the positive ion - towards the cathode. On its way, the electron meets ions and neutral atoms. In the intervals between two successive collisions, the energy of the electron increases due to the work of the electric field forces.

The greater the potential difference between the electrodes, the greater the electric field strength. The kinetic energy of an electron before the next collision is proportional to the field strength and the free path of the electron: MV 2 /2=eEl. If the kinetic energy of an electron exceeds the work A i that needs to be done in order to ionize a neutral atom (or molecule), i.e. MV 2 >A i , then when an electron collides with an atom (or molecule), it is ionized. As a result, instead of one electron, two electrons appear (attacking on the atom and torn out of the atom). They, in turn, receive energy in the field and ionize the oncoming atoms, etc. As a result, the number of charged particles increases rapidly, and an electron avalanche arises. The described process is called electron impact ionization.

But ionization by electron impact alone cannot ensure the maintenance of an independent charge. Indeed, after all, all the electrons that arise in this way move towards the anode and, upon reaching the anode, "drop out of the game." To maintain the discharge requires the emission of electrons from the cathode ("emission" means "emission"). The emission of an electron can be due to several reasons.

Positive ions, formed during the collision of electrons with neutral atoms, in their movement to the cathode acquire a large kinetic energy under the action of the field. When such fast ions hit the cathode, electrons are knocked out from the cathode surface.

In addition, the cathode can emit electrons when heated to a high temperature. This process is called thermionic emission. It can be considered as the evaporation of electrons from the metal. In many solid substances, thermionic emission occurs at temperatures at which the evaporation of the substance itself is still small. Such substances are used for the manufacture of cathodes.

During self-discharge, the cathode can be heated by bombarding it with positive ions. If the energy of the ions is not too high, then there is no knocking out of electrons from the cathode and electrons are emitted due to thermionic emission.

6. Various types of self-discharge and their technical application.

Depending on the properties and state of the gas, the nature and location of the electrodes, as well as the voltage applied to the electrodes, various types of self-discharge occur. Let's consider a few of them.

A. Smoldering discharge.

A glow discharge is observed in gases at low pressures of the order of several tens of millimeters of mercury and less. If we consider a tube with a glow discharge, we can see that the main parts of a glow discharge are cathode Dark Space, far away from him negative or smoldering glow, which gradually passes into the area faraday dark space. These three regions form the cathode part of the discharge, followed by the main luminous part of the discharge, which determines its optical properties and is called positive column.

The main role in maintaining the glow discharge is played by the first two regions of its cathode part. A characteristic feature of this type of discharge is a sharp drop in the potential near the cathode, which is associated with a high concentration of positive ions at the boundary of regions I and II, due to the relatively low velocity of ions near the cathode. In the cathode dark space, there is a strong acceleration of electrons and positive ions, knocking out electrons from the cathode. In the region of glowing glow, electrons produce intense impact ionization of gas molecules and lose their energy. Here, positive ions are formed, which are necessary to maintain the discharge. The electric field strength in this region is low. The smoldering glow is mainly caused by the recombination of ions and electrons. The length of the cathode dark space is determined by the properties of the gas and cathode material.

In the region of the positive column, the concentration of electrons and ions is approximately the same and very high, which causes a high electrical conductivity of the positive column and a slight drop in potential in it. The glow of the positive column is determined by the glow of excited gas molecules. Near the anode, a relatively sharp change in the potential is again observed, which is associated with the process of generation of positive ions. In some cases, the positive column breaks up into separate luminous areas - strata, separated by dark spaces.

The positive column does not play a significant role in maintaining the glow discharge; therefore, as the distance between the electrodes of the tube decreases, the length of the positive column decreases and it may disappear altogether. The situation is different with the length of the cathode dark space, which does not change when the electrodes approach each other. If the electrodes are so close that the distance between them becomes less than the length of the cathode dark space, then the glow discharge in the gas will stop. Experiments show that, other things being equal, the length d of the cathode dark space is inversely proportional to the gas pressure. Consequently, at sufficiently low pressures, electrons knocked out of the cathode by positive ions pass through the gas almost without collisions with its molecules, forming electronic, or cathode rays .

Glow discharge is used in gas-light tubes, fluorescent lamps, voltage stabilizers, to obtain electron and ion beams. If a slit is made in the cathode, then narrow ion beams pass through it into the space behind the cathode, often called channel rays. widely used phenomenon cathode sputtering, i.e. destruction of the cathode surface under the action of positive ions hitting it. Ultramicroscopic fragments of the cathode material fly in all directions along straight lines and cover the surface of bodies (especially dielectrics) placed in a tube with a thin layer. In this way, mirrors are made for a number of devices, a thin layer of metal is applied to selenium photocells.

b. Corona discharge.

A corona discharge occurs at normal pressure in a gas in a highly inhomogeneous electric field (for example, near spikes or wires of high voltage lines). In a corona discharge, gas ionization and its glow occur only near the corona electrodes. In the case of cathode corona (negative corona), electrons that cause impact ionization of gas molecules are knocked out of the cathode when it is bombarded with positive ions. If the anode is corona (positive corona), then the birth of electrons occurs due to the photoionization of the gas near the anode. Corona is a harmful phenomenon, accompanied by current leakage and loss of electrical energy. To reduce corona, the radius of curvature of the conductors is increased, and their surface is made as smooth as possible. At a sufficiently high voltage between the electrodes, the corona discharge turns into a spark.

At an increased voltage, the corona discharge on the tip takes the form of light lines emanating from the tip and alternating in time. These lines, having a series of kinks and bends, form a kind of brush, as a result of which such a discharge is called carpal .

A charged thundercloud induces electric charges of the opposite sign on the Earth's surface under it. A particularly large charge accumulates on the tips. Therefore, before a thunderstorm or during a thunderstorm, cones of light like brushes often flare up on the points and sharp corners of highly raised objects. Since ancient times, this glow has been called the fires of St. Elmo.

Especially often climbers become witnesses of this phenomenon. Sometimes even not only metal objects, but also the ends of the hair on the head are decorated with small luminous tassels.

Corona discharge has to be considered when dealing with high voltage. If there are protruding parts or very thin wires, corona discharge can start. This results in power leakage. The higher the voltage of the high-voltage line, the thicker the wires should be.

C. Spark discharge.

The spark discharge has the appearance of bright zigzag branching filaments-channels that penetrate the discharge gap and disappear, being replaced by new ones. Studies have shown that the channels of the spark discharge begin to grow sometimes from the positive electrode, sometimes from the negative, and sometimes from some point between the electrodes. This is explained by the fact that impact ionization in the case of a spark discharge occurs not over the entire volume of gas, but through individual channels passing in those places where the ion concentration accidentally turned out to be the highest. A spark discharge is accompanied by the release of a large amount of heat, a bright glow of gas, crackling or thunder. All these phenomena are caused by electron and ion avalanches that occur in spark channels and lead to a huge increase in pressure, reaching 10 7 ¸10 8 Pa, and an increase in temperature up to 10,000 °C.

A typical example of a spark discharge is lightning. The main lightning channel has a diameter of 10 to 25 cm, and the lightning length can reach several kilometers. The maximum current of a lightning pulse reaches tens and hundreds of thousands of amperes.

With a small length of the discharge gap, the spark discharge causes a specific destruction of the anode, called erosion. This phenomenon was used in the electrospark method of cutting, drilling and other types of precision metal processing.

The spark gap is used as a surge protector in electrical transmission lines (eg telephone lines). If a strong short-term current passes near the line, then voltages and currents are induced in the wires of this line, which can destroy the electrical installation and are dangerous to human life. To avoid this, special fuses are used, consisting of two curved electrodes, one of which is connected to the line and the other is grounded. If the potential of the line relative to the ground increases greatly, then a spark discharge occurs between the electrodes, which, together with the air heated by it, rises up, lengthens and breaks.

Finally, an electric spark is used to measure large potential differences using ball gap, whose electrodes are two metal balls with a polished surface. The balls are moved apart, and a measured potential difference is applied to them. Then the balls are brought together until a spark jumps between them. Knowing the diameter of the balls, the distance between them, the pressure, temperature and humidity of the air, they find the potential difference between the balls according to special tables. This method can be used to measure, to within a few percent, potential differences of the order of tens of thousands of volts.

D. Arc discharge.

The arc discharge was discovered by V. V. Petrov in 1802. This discharge is one of the forms of gas discharge, which occurs at a high current density and a relatively low voltage between the electrodes (on the order of several tens of volts). The main cause of the arc discharge is the intense emission of thermoelectrons by a hot cathode. These electrons are accelerated by an electric field and produce impact ionization of gas molecules, due to which the electrical resistance of the gas gap between the electrodes is relatively small. If we reduce the resistance of the external circuit, increase the current of the arc discharge, then the conductivity of the gas gap will increase so much that the voltage between the electrodes decreases. Therefore, the arc discharge is said to have a falling current-voltage characteristic. At atmospheric pressure, the cathode temperature reaches 3000 °C. Electrons, bombarding the anode, create a recess (crater) in it and heat it. The temperature of the crater is about 4000 °C, and at high air pressures it reaches 6000-7000 °C. The temperature of the gas in the arc discharge channel reaches 5000-6000 °C, so intense thermal ionization occurs in it.

In a number of cases, an arc discharge is also observed at a relatively low cathode temperature (for example, in a mercury arc lamp).

In 1876, P. N. Yablochkov first used an electric arc as a light source. In the "Yablochkov candle", the coals were arranged in parallel and separated by a curved layer, and their ends were connected by a conductive "ignition bridge". When the current was turned on, the ignition bridge burned out and an electric arc formed between the coals. As the coals burned, the insulating layer evaporated.

The arc discharge is used as a source of light even today, for example, in searchlights and projectors.

The high temperature of the arc discharge makes it possible to use it for the construction of an arc furnace. At present, arc furnaces powered by a very high current are used in a number of industries: for the smelting of steel, cast iron, ferroalloys, bronze, the production of calcium carbide, nitrogen oxide, etc.

In 1882, N. N. Benardos first used an arc discharge for cutting and welding metal. The discharge between a fixed carbon electrode and metal heats up the junction of two metal sheets (or plates) and welds them. Benardos used the same method to cut metal plates and make holes in them. In 1888, N. G. Slavyanov improved this welding method by replacing the carbon electrode with a metal one.

The arc discharge has found application in a mercury rectifier, which converts an alternating electric current into a direct current.

E. Plasma.

Plasma is a partially or fully ionized gas in which the densities of positive and negative charges are almost the same. Thus, plasma as a whole is an electrically neutral system.

The quantitative characteristic of plasma is the degree of ionization. The degree of plasma ionization a is the ratio of the volume concentration of charged particles to the total volume concentration of particles. Depending on the degree of ionization, plasma is divided into weakly ionized(a is fractions of a percent), partially ionized (a of the order of a few percent) and fully ionized (a is close to 100%). Weakly ionized plasma in natural conditions are the upper layers of the atmosphere - the ionosphere. The sun, hot stars, and some interstellar clouds are fully ionized plasma that forms at high temperatures.

The average energies of various types of particles that make up a plasma can differ significantly from one another. Therefore, plasma cannot be characterized by a single value of temperature T; Distinguish between the electron temperature T e, the ion temperature T i (or ion temperatures, if there are several kinds of ions in the plasma) and the temperature of neutral atoms T a (neutral component). Such a plasma is called non-isothermal, in contrast to isothermal plasma, in which the temperatures of all components are the same.

Plasma is also divided into high-temperature (T i »10 6 -10 8 K and more) and low-temperature!!! (T i<=10 5 К). Это условное разделение связано с особой влажностью высокотемпературной плазмы в связи с проблемой осуществления управляемого термоядерного синтеза.

Plasma has a number of specific properties, which allows us to consider it as a special fourth state of matter.

Due to the high mobility of charged plasma particles, they easily move under the influence of electric and magnetic fields. Therefore, any violation of the electrical neutrality of individual regions of the plasma, caused by the accumulation of particles of the same charge sign, is quickly eliminated. The resulting electric fields move charged particles until electrical neutrality is restored and the electric field becomes zero. In contrast to a neutral gas, between whose molecules there are short-range forces, between charged plasma particles there are Coulomb forces that decrease relatively slowly with distance. Each particle interacts immediately with a large number of surrounding particles. Due to this, along with chaotic thermal motion, plasma particles can participate in various ordered motions. Various types of oscillations and waves are easily excited in a plasma.

The plasma conductivity increases as the degree of ionization increases. At high temperatures, a fully ionized plasma approaches superconductors in its conductivity.

Low-temperature plasma is used in gas-discharge light sources - in luminous tubes for advertising inscriptions, in fluorescent lamps. A gas discharge lamp is used in many devices, for example, in gas lasers - quantum light sources.

High-temperature plasma is used in magnetohydrodynamic generators.

A new device, the plasma torch, has recently been created. The plasmatron creates powerful jets of dense low-temperature plasma, which are widely used in various fields of technology: for cutting and welding metals, drilling wells in hard rocks, etc.

List of used literature:

1) Physics: Electrodynamics. 10-11 cells: textbook. for in-depth study of physics / G. Ya. Myakishev, A. Z. Sinyakov, B. A. Slobodskov. - 2nd edition - M.: Drofa, 1998. - 480 p.

2) Physics course (in three volumes). T. II. electricity and magnetism. Proc. manual for technical colleges. / Detlaf A.A., Yavorsky B. M., Milkovskaya L. B. Izd. 4th, revised. - M.: Higher School, 1977. - 375 p.

3) Electricity./E. G. Kalashnikov. Ed. "Science", Moscow, 1977.

4) Physics./B. B. Bukhovtsev, Yu. L. Klimontovich, G. Ya. Myakishev. 3rd edition, revised. – M.: Enlightenment, 1986.