Slide 2
Electric current is the ordered movement of charged particles. To obtain electric current in a conductor, it is necessary to create an electric field in it. Under the influence of this field, charged particles that can move freely in this conductor will begin to move in the direction of the action of electrical forces on them. An electric current arises. In order for an electric current to exist in a conductor for a long time, it is necessary to maintain an electric field in it all this time. An electric field in conductors is created and can be maintained for a long time by sources of electric current.
Slide 3
Current source poles
There are different current sources, but in each of them work is done to separate positively and negatively charged particles. The separated particles accumulate at the poles of the current source. This is the name of the places to which conductors are connected using terminals or clamps. One pole of the current source is charged positively, and the other - negatively.
Slide 4
Current sources
In current sources, in the process of separating charged particles, mechanical work is converted into electrical work. For example, in an electrophore machine (see figure), mechanical energy is converted into electrical energy
Slide 5
Electric circuit and its components
In order to use the energy of electric current, you must first have a source of current. Electric motors, lamps, tiles, all kinds of electrical household appliances are called receivers or consumers of electrical energy.
Slide 6
Symbols used in diagrams
Electrical energy must be delivered to the receiver. To do this, the receiver is connected to a source of electrical energy by wires. To turn receivers on and off at the right time, keys, switches, buttons, and switches are used. The current source, receivers, closing devices connected to each other by wires make up the simplest electrical circuit. For there to be current in the circuit, it must be closed. If the wire breaks in some place, the current in the circuit will stop.
Slide 7
Scheme
Drawings that show methods of connecting electrical devices into a circuit are called diagrams. Figure a) shows an example of an electrical circuit.
Slide 8
Electric current in metals
Electric current in metals is the ordered movement of free electrons. Evidence that the current in metals is caused by electrons was the experiments of physicists from our country L.I. Mendelshtam and N.D. Papaleksi (see figure), as well as American physicists B. Stewart and Robert Tolman.
Slide 9
Metal lattice nodes
Positive ions are located at the nodes of the metal crystal lattice, and free electrons move in the space between them, i.e., not associated with the nuclei of their atoms (see figure). The negative charge of all free electrons is equal in absolute value to the positive charge of all lattice ions. Therefore, under normal conditions the metal is electrically neutral.
Slide 10
Electron movement
When an electric field is created in a metal, it acts on the electrons with some force and imparts acceleration in the direction opposite to the direction of the field strength vector. Therefore, in an electric field, randomly moving electrons are displaced in one direction, i.e. move in an orderly manner.
Slide 11
The movement of electrons is partly reminiscent of the drift of ice floes during ice drift...
When they, moving randomly and colliding with each other, drift along the river. The ordered movement of conduction electrons constitutes electric current in metals.
Slide 12
Action of electric current.
We can judge the presence of electric current in a circuit only by the various phenomena that electric current causes. Such phenomena are called current actions. Some of these actions are easy to observe experimentally.
Slide 13
Thermal effect of current...
...can be observed, for example, by connecting iron or nickel wire to the poles of a current source. At the same time, the wire heats up and, having lengthened, sags slightly. It can even be red hot. In electric lamps, for example, a thin tungsten wire is heated by current and produces a bright glow
Slide 14
The chemical effect of current...
... is that in some acid solutions, when an electric current passes through them, a release of substances is observed. Substances contained in the solution are deposited on electrodes immersed in this solution. For example, when current is passed through a solution of copper sulfate, pure copper will be released at a negatively charged electrode. This is used to obtain pure metals.
Slide 15
Magnetic effect of current...
... can also be observed experimentally. To do this, a copper wire covered with insulating material must be wound around an iron nail, and the ends of the wire must be connected to a current source. When the circuit is closed, the nail becomes a magnet and attracts small iron objects: nails, iron filings, filings. With the disappearance of the current in the winding, the nail is demagnetized.
Slide 16
Let us now consider the interaction between a current-carrying conductor and a magnet.
The picture shows a small frame hanging on threads, on which several turns of thin copper wire are wound. The ends of the winding are connected to the poles of the current source. Consequently, there is an electric current in the winding, but the frame hangs motionless. If the frame is now placed between the poles of the magnet, it will begin to rotate.
Slide 17
Direction of electric current.
Since in most cases we are dealing with electric current in metals, it would be reasonable to take the direction of movement of electrons in the electric field as the direction of the current in the circuit, i.e. assume that the current is directed from the negative pole of the source to the positive. The direction of the current was conventionally taken to be the direction in which positive charges move in the conductor, i.e. direction from the positive pole of the current source to the negative. This is taken into account in all the rules and laws of electric current.
Slide 18
Current strength. Units of current strength.
The electric charge passing through the cross section of the conductor in 1 s determines the current strength in the circuit. This means that the current strength is equal to the ratio of the electric charge q passing through the cross section of the conductor to the time of its passage t. Where I is the current strength.
Slide 19
Experience on the interaction of two conductors with current.
At the International Conference on Weights and Measures in 1948, it was decided to base the definition of the unit of current on the phenomenon of interaction of two conductors with current. Let's first get acquainted with this phenomenon experimentally...
Slide 20
Experience
The figure shows two flexible straight conductors located parallel to each other. Both conductors are connected to a current source. When a circuit is closed, current flows through the conductors, as a result of which they interact - they attract or repel, depending on the direction of the currents in them. The force of interaction between conductors and current can be measured; it depends on the length of the conductor, the distance between them, the environment in which the conductors are located, and the strength of the current in the conductors.
Slide 21
Units of current.
The unit of current is the current at which sections of such parallel conductors 1 m long interact with a force of 0.0000002 N. This unit of current is called ampere (A). Since it is named after the French scientist Andre Ampere.
When measuring current, the ammeter is connected in series with the device in which the current is measured. In a circuit consisting of a current source and a series of conductors connected so that the end of one conductor is connected to the beginning of another, the current strength in all sections is the same.
Slide 25
Current strength is a very important characteristic of an electrical circuit. Those working with electrical circuits should know that a current of up to 1 Ma is considered safe for the human body. Current strength greater than 100 Ma leads to serious damage to the body.
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Slide 1
Lecture plan 1. The concept of conduction current. Current vector and current strength. 2. Differential form of Ohm's law. 3. Serial and parallel connection of conductors. 4. The reason for the appearance of an electric field in a conductor, the physical meaning of the concept of external forces. 5. Derivation of Ohm's law for the entire circuit. 6. Kirchhoff's first and second rules. 7. Contact potential difference. Thermoelectric phenomena. 8. Electric current in various environments. 9. Current in liquids. Electrolysis. Faraday's laws.
Slide 2
Electric current is the orderly movement of electric charges. Current carriers can be electrons, ions, and charged particles. If an electric field is created in a conductor, then free electric charges in it will begin to move - a current appears, called conduction current. If a charged body moves in space, then the current is called convection. 1. The concept of conduction current. Current vector and current strength
Slide 3
The direction of current is usually taken to be the direction of movement of positive charges. For the occurrence and existence of current it is necessary: 1. the presence of free charged particles; 2.presence of an electric field in the conductor. The main characteristic of current is the current strength, which is equal to the amount of charge passing through the cross-section of the conductor in 1 second.
Slide 4
Where q is the amount of charge; t – charge transit time;
Slide 5
Current strength is a scalar quantity.
Slide 6
In 1826, the German physicist Ohm experimentally established that the current strength J in a conductor is directly proportional to the voltage U between its ends. Where k is the proportionality coefficient, called electrical conductivity or conductivity; [k] = [Sm] (Siemens).
Slide 7
The quantity is called the electrical resistance of the conductor. Ohm's law for a section of an electrical circuit that does not contain a current source 2. Differential form of Ohm's law
Slide 8
We express from this formula R Electrical resistance depends on the shape, size and substance of the conductor. The resistance of a conductor is directly proportional to its length l and inversely proportional to its cross-sectional area S Where characterizes the material from which the conductor is made and is called the resistivity of the conductor.
Slide 9
Let us express : The resistance of the conductor depends on the temperature. As the temperature increases, the resistance increases. WhereR0 is the resistance of the conductor at 0С; t – temperature; – temperature coefficient of resistance (for metal 0.04 deg-1). The formula is also valid for resistivity. Where0 is the resistivity of the conductor at 0С.
Slide 10
At low temperatures (
Slide 11
Let's rearrange the terms of the expression Where I/S=j – current density;
Slide 12
1/= – specific conductivity of the conductor substance; U/l=E – electric field strength in the conductor. Ohm's law in differential form.
Ohm's law for a homogeneous section of a chain. Differential form of Ohm's law.
Slide 13
3. Series and parallel connection of conductors
Slide 14
Series connection of conductors I=const (according to the law of conservation of charge); U=U1+U2 Rtot=R1+R2+R3 Rtot=Ri R=N*R1 (For N identical conductors) R1 R2 R3
Slide 15
Due to this, a potential difference is maintained at the ends of the external circuit and a constant electric current flows in the circuit. Extraneous forces cause the separation of unlike charges and maintain a potential difference at the ends of the conductor.
Slide 16
An additional electric field of external forces in a conductor is created by current sources (galvanic cells, batteries, electric generators).
Slide 17
EMF of a current source The physical quantity equal to the work of external forces to move a single positive charge between the poles of the source is called the electromotive force of the current source (EMF).
Slide 18
Ohm's Law for a non-uniform section of a circuit
5. Derivation of Ohm's law for a closed electrical circuit
Slide 19
Let a closed electrical circuit consist of a current source with , with internal resistance r and an external part with resistance R. R is external resistance; r – internal resistance.
Slide 20
where is the voltage across the external resistance;
Slide 21
A – work on moving charge q inside the current source, i.e. work on internal resistance.
Then since, we rewrite the expression for : , Since according to Ohm’s law for a closed electrical circuit ( = IR) IR and Ir are the voltage drop on the external and internal sections of the circuit,
That is Ohm's law for a closed electrical circuit. In a closed electrical circuit, the electromotive force of the current source is equal to the sum of the voltage drops in all sections of the circuit.
6. Kirchhoff's first and second rules The first Kirchhoff rule is the condition for constant current in the circuit. The algebraic sum of the current strength in the branching node is equal to zero where n is the number of conductors;
Ii – currents in conductors.
Currents approaching the node are considered positive, and currents leaving the node are considered negative. For node A, the first Kirchhoff rule will be written:
Slide 22
Slide 25
To create an equation, you need to select the direction of traversal (clockwise or counterclockwise). All currents coinciding in direction with the circuit bypass are considered positive. The EMF of current sources is considered positive if they create a current directed towards bypassing the circuit. So, for example, Kirchhoff’s rule for parts I, II, III. I I1r1 + I1R1 + I2r2 + I2R2 = – 1 –2 II–I2r2 – I2R2 + I3r3 + I3R3= 2 + 3 IIII1r1 + I1R1 + I3r3 + I3R3 = – 1 + 3 Based on these equations, the circuits are calculated.
Slide 26
7. Contact potential difference. Thermoelectric phenomena Electrons with the greatest kinetic energy can fly out of the metal into the surrounding space. As a result of the emission of electrons, an “electron cloud” is formed. There is a dynamic equilibrium between the electron gas in the metal and the “electron cloud”. The work function of an electron is the work that must be done to remove an electron from a metal into airless space. The surface of the metal is an electrical double layer, similar to a very thin capacitor.
Slide 27
The potential difference between the capacitor plates depends on the work function of the electron. Where is the electron charge; – contact potential difference between the metal and the environment; A – work function (electron-volt – E-V). The work function depends on the chemical nature of the metal and the condition of its surface (pollution, moisture).
Slide 28
Volta's laws: 1. When two conductors made of different metals are connected, a contact potential difference arises between them, which depends only on the chemical composition and temperature. 2. The potential difference between the ends of a circuit consisting of metal conductors connected in series, located at the same temperature, does not depend on the chemical composition of the intermediate conductors. It is equal to the contact potential difference that arises when the outermost conductors are directly connected.
Slide 29
Let's consider a closed circuit consisting of two metal conductors 1 and 2. The emf applied to this circuit is equal to the algebraic sum of all potential jumps. If the temperatures of the layers are equal, then =0. If the temperatures of the layers are different, for example, then Where is a constant characterizing the properties of the contact of two metals. In this case, a thermoelectromotive force appears in a closed circuit, directly proportional to the temperature difference between both layers.
Slide 30
Thermoelectric phenomena in metals are widely used to measure temperature. For this, thermoelements or thermocouples are used, which are two wires made of various metals and alloys. The ends of these wires are soldered. One junction is placed in a medium whose temperature T1 needs to be measured, and the second junction is placed in a medium with a constant known temperature. Thermocouples have a number of advantages over conventional thermometers: they allow you to measure temperatures in a wide range from tens to thousands of degrees of the absolute scale.
Slide 31
Gases under normal conditions are dielectrics R => ∞, consisting of electrically neutral atoms and molecules. When gases are ionized, electric current carriers (positive charges) appear. Electric current in gases is called gas discharge. To carry out a gas discharge, there must be an electric or magnetic field to the tube with ionized gas.
Slide 32
Gas ionization is the disintegration of a neutral atom into a positive ion and an electron under the influence of an ionizer (external influences - strong heating, ultraviolet and x-rays, radioactive radiation, bombardment of gas atoms (molecules) by fast electrons or ions). Ion electron atom neutral
Slide 33
A measure of the ionization process is the ionization intensity, measured by the number of pairs of oppositely charged particles appearing in a unit volume of gas in a unit time period. Impact ionization is the separation of one or more electrons from an atom (molecule), caused by the collision of electrons or ions accelerated by an electric field in a discharge with atoms or molecules of a gas.
Slide 34
Recombination is the joining of an electron with an ion to form a neutral atom. If the action of the ionizer stops, the gas again becomes dialectic. electron ion
Slide 35
1. A non-self-sustaining gas discharge is a discharge that exists only under the influence of external ionizers. Current-voltage characteristics of a gas discharge: as U increases, the number of charged particles reaching the electrode increases and the current increases to I = Ik, at which all charged particles reach the electrodes. In this case, U=Uk saturation current Where e is the elementary charge; N0 is the maximum number of pairs of monovalent ions formed in the volume of gas in 1 s.
Slide 36
2. Self-sustaining gas discharge – a discharge in a gas that persists after the external ionizer stops operating. Maintained and developed due to impact ionization.
A non-self-sustaining gas discharge becomes independent at Uз – ignition voltage. The process of such a transition is called electrical breakdown of the gas. There are:
Slide 37
Corona discharge – occurs at high pressure and in a sharply inhomogeneous field with a large curvature of the surface, used in the disinfection of agricultural seeds. Glow discharge – occurs at low pressures, used in gas-light tubes and gas lasers. Spark discharge - at P = Ratm and at large electric fields - lightning (currents up to several thousand Amperes, length - several kilometers). Arc discharge - occurs between closely spaced electrodes, (T = 3000 °C - at atmospheric pressure. Used as a light source in powerful spotlights, in projection equipment.
Slide 38
Plasma is a special state of aggregation of a substance, characterized by a high degree of ionization of its particles. Plasma is divided into: – weakly ionized ( – fractions of a percent – upper layers of the atmosphere, ionosphere); – partially ionized (several%); – fully ionized (sun, hot stars, some interstellar clouds).
Artificially created plasma is used in gas-discharge lamps, plasma sources of electrical energy, and magnetodynamic generators.
Slide 39
In solids, an electron interacts not only with its own atom, but also with other atoms of the crystal lattice, and the energy levels of the atoms are split to form an energy band. The energy of these electrons may lie within shaded regions called allowed energy bands. Discrete levels are separated by areas of prohibited energy values - forbidden zones (their width is commensurate with the width of the forbidden zones).
The differences in the electrical properties of various types of solids are explained by: 1) the width of the energy gaps; 2) different filling of allowed energy bands with electrons
Slide 41
Many liquids conduct electricity very poorly (distilled water, glycerin, kerosene, etc.). Aqueous solutions of salts, acids and alkalis conduct electricity well. Electrolysis is the passage of current through a liquid, causing the release of substances that make up the electrolyte on the electrodes. Electrolytes are substances with ionic conductivity. Ionic conductivity is the ordered movement of ions under the influence of an electric field. Ions are atoms or molecules that have lost or gained one or more electrons. Positive ions are cations, negative ions are anions.
Slide 42
An electric field is created in the liquid by electrodes (“+” – anode, “–” – cathode). Positive ions (cations) move towards the cathode, negative ions move towards the anode. The appearance of ions in electrolytes is explained by electrical dissociation - the disintegration of molecules of a soluble substance into positive and negative ions as a result of interaction with the solvent (Na+Cl-; H+Cl-; K+I-...). The degree of dissociation α is the number of molecules n0 dissociated into ions to the total number of molecules n0. During the thermal movement of ions, the reverse process of reunification of ions, called recombination, also occurs.
Slide 43
M. Faraday's laws (1834). 1. The mass of the substance released on the electrode is directly proportional to the electric charge q passing through the electrolyte or Where k is the electrochemical equivalent of the substance; equal to the mass of the substance released when a unit amount of electricity passes through the electrolyte. Where I is the direct current passing through the electrolyte.
Slide 46
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Electric current Electric current is the ordered (directed) movement of electric charges. Conduction current (current in conductors) is the movement of microcharges in a macrobody. Convection current is the movement of macroscopic charged bodies in space. Current in a vacuum is the movement of microcharges in a vacuum.
Electric current In a conductor, under the influence of an applied electric field, free electric charges move: positive - along the field, negative - against the field. Charge carriers perform a complex movement: 1) chaotic with an average speed v ~ (10 3 ÷ 10 4 m/s), 2) directed with an average speed v ~ E (fractions of mm/s).
Thus, the average speed of directional motion of electrons is much less than the average speed of their chaotic motion. The low average speed of directed motion is explained by their frequent collisions with ions of the crystal lattice. At the same time, any change in the electric field is transmitted along the wires at a speed equal to the speed of propagation of the electromagnetic wave - (3·10 8 m/s). Therefore, the movement of electrons under the influence of an external field occurs along the entire length of the wire almost simultaneously with the application of the signal.
When charges move, their equilibrium distribution is disrupted. Consequently, the surface of the conductor is no longer equipotential and the electric field strength vector E is not directed perpendicular to the surface, since for the movement of charges it is necessary that E τ 0 on the surface. For this reason, there is an electric field inside the conductor, which is equal to zero only in the case of an equilibrium distribution charges on the surface of a conductor.
Conditions for the appearance and existence of conduction current: 1. The presence of free charge carriers in the medium, i.e. charged particles that can move. In a metal these are conduction electrons; in electrolytes – positive and negative ions; in gases - positive, negative ions and electrons.
Conditions for the appearance and existence of conduction current: 2. The presence of an electric field in the medium, the energy of which would be spent on the movement of electric charges. In order for the current to last, the energy of the electric field must be replenished all the time, i.e. you need a source of electrical energy - a device in which any energy is converted into the energy of an electric field.
– the current strength is numerically equal to the charge passing through the cross section of the conductor per unit time. In SI: . The movement of charge carriers of one sign is equivalent to the movement of charge carriers of the opposite sign in the opposite direction. If the current is created by two types of carriers:
Outside forces. Electromotive force. Voltage If the current carriers in a circuit are affected only by the force of the electrostatic field, then the carriers move, which leads to equalization of potentials at all points of the circuit and to the disappearance of the electric field. Therefore, for the existence of direct current, it is necessary to have a device in the circuit that creates and maintains a potential difference φ due to the work of forces of non-electrical origin. Such devices are called current sources (generators - mechanical energy is converted; batteries - the energy of a chemical reaction between the electrodes and the electrolyte).
Outside forces. Electromotive force. Third-party forces of non-electric origin acting on charges from current sources. Due to the field of external forces, electric charges move inside the current source against the forces of the electrostatic field. Consequently, a potential difference is maintained at the ends of the external circuit and a constant current flows in the circuit.
Outside forces. Electromotive force. External forces do work to move electric charges. Electromotive force (emf - E) is a physical quantity determined by the work done by external forces when moving a single positive charge
Ohm's law for a homogeneous section of a circuit A section of a circuit that does not contain a source of emf is called homogeneous. Ohm's law in integral form: the current is directly proportional to the voltage drop across a homogeneous section of the circuit and inversely proportional to the resistance of this section.
Ohm's law is not a universal relationship between current and voltage. a) Current in gases and semiconductors obeys Ohm’s law only at small U. b) Current in a vacuum does not obey Ohm’s law. Boguslavsky-Langmuir law (law 3/2): I ~ U 3/2. c) in an arc discharge - as the current increases, the voltage drops. Disobedience to Ohm's law is due to the dependence of resistance on current.
Ohm's Law In SI, resistance R is measured in ohms. The value of R depends on the shape and size of the conductor, as well as on the properties of the material from which it is made. For a cylindrical conductor: where ρ is the electrical resistivity [Ohm m], for metals its value is about 10 –8 Ohm m.
The resistance of a conductor depends on its temperature: α is the temperature coefficient of resistance, for pure metals (at not very low temperatures α 1 / 273 K -1, ρ 0, R 0 are, respectively, the resistivity and resistance of the conductor at t = 0 o C. Such the dependence ρ(t) is explained by the fact that with increasing temperature, the intensity of the chaotic movement of positive ions of the crystal lattice increases, and the directional movement of electrons is inhibited.
Ohm's law for a non-uniform section of a circuit Non-uniform is a section of a circuit containing a source of emf. A closed circuit contains a source of emf, which in direction 1–2 promotes the movement of positive charges. E is the field strength of Coulomb forces, E st is the field strength of external forces.
Ohm's law for an inhomogeneous section of a circuit The work done by Coulomb and external forces to move a single positive charge q 0+ is the voltage drop (voltage). Since points 1, 2 were chosen arbitrarily, the resulting relations are valid for any two points of the electrical circuit:
Work and power of electric current Joule-Lenz Law When free electrons collide with ions of a crystal lattice, they transfer to the ions excess kinetic energy, which they acquire during accelerated movement in an electric field. As a result of these collisions, the amplitude of vibrations of the ions near the nodes of the crystal lattice increases (the thermal movement of the ions becomes more intense). Consequently, the conductor heats up: temperature is a measure of the intensity of the chaotic movement of atoms and molecules. The released heat Q is equal to the work done by the current A.
Kirchhoff's laws Used to calculate branched DC circuits. An unbranched electrical circuit is a circuit in which all elements of the circuit are connected in series. An electrical circuit element is any device included in an electrical circuit. An electrical circuit node is a point in a branched circuit where more than two conductors converge. A branch of a branched electrical circuit is a section of a circuit between two nodes.
Kirchhoff's second law (generalized Ohm's law): in any closed circuit, arbitrarily chosen in a branched electrical circuit, the algebraic sum of the products of the current strengths I i and the resistance of the corresponding sections R i of this circuit is equal to the algebraic sum of the emf. in the circuit.
Kirchhoff's second law The current is considered positive if its direction coincides with the conditionally selected direction of the circuit bypass. E.m.f. is considered positive if the direction of the bypass is from – to + the current source, i.e. e.m.f. creates a current coinciding with the direction of bypass.
The procedure for calculating a branched circuit: 1. Arbitrarily select and indicate on the drawing the direction of the current in all sections of the circuit. 2. Count the number of nodes in the chain (m). Write Kirchhoff's first law for each of the (m-1) nodes. 3. Select arbitrarily closed contours in the circuit, arbitrarily select directions for traversing the contours. 4. Write Kirchhoff’s second law for contours. If the chain consists of p-branches and m-nodes, then the number of independent equations of Kirchhoff’s 2nd law is (p-m+1).
Slide 1
Physics teacher at Nevinnomyssk Energy Technical School Pak Olga Ben-Ser
"Electric current in gases"
Slide 2
The process of current flowing through gases is called an electrical discharge in gases. The breakdown of gas molecules into electrons and positive ions is called gas ionization
At room temperatures, gases are dielectrics. Heating a gas or irradiating it with ultraviolet, x-rays and other rays causes the ionization of atoms or molecules of the gas. The gas becomes a conductor.
Slide 3
Charge carriers arise only during ionization. Charge carriers in gases – electrons and ions
If ions and free electrons find themselves in an external electric field, then they begin to move in a direction and create an electric current in the gases.
Mechanism of electrical conductivity of gases
Slide 4
Non-self-sustaining discharge
The phenomenon of electric current flowing through a gas, observed only under the condition of some external influence on the gas, is called a non-self-sustaining electric discharge. If there is no voltage on the electrodes, the galvanometer connected to the circuit will show zero. With a small potential difference between the electrodes of the tube, charged particles begin to move, and a gas discharge occurs. But not all the resulting ions reach the electrodes. As the potential difference between the electrodes of the tube increases, the current in the circuit also increases.
Slide 5
Non-self-sustaining discharge
At a certain voltage, when all the charged particles formed in the gas by the ionizer per second reach the electrodes during this time. The current reaches saturation. Current-voltage characteristics of a non-self-sustaining discharge
Slide 6
The phenomenon of electric current passing through a gas, independent of external ionizers, is called an independent gas discharge in a gas. The electron, accelerated by the electric field, collides with ions and neutral molecules on its way to the anode. Its energy is proportional to the field strength and the mean free path of the electron. If the kinetic energy of the electron exceeds the work that must be done to ionize the atom, then when the electron collides with the atom, it is ionized, called electron impact ionization.
An avalanche-like increase in the number of charged particles in a gas can begin under the influence of a strong electric field. In this case, the ionizer is no longer needed.
Self discharge
Slide 7
Slide 8
A corona discharge is observed at atmospheric pressure in a gas located in a highly inhomogeneous electric field (near tips, high voltage line wires, etc.), the luminous region of which often resembles a corona (that’s why it was called corona)
Types of self-discharge
Slide 9
Spark discharge - An intermittent discharge in a gas that occurs at high electric field strength (about 3MV/m) in air at atmospheric pressure.
Types of self-discharge
A spark discharge, unlike a corona discharge, leads to breakdown of the air gap.
application: lightning, for igniting a combustible mixture in an internal combustion engine, electric spark processing of metals
Types of self-discharge