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Physics teacher at Nevinnomyssk Energy Technical School Pak Olga Ben-Ser
"Electric current in gases"

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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.

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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

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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.

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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

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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

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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

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Spark discharge - An intermittent discharge in a gas that occurs at high electric field strength (about 3MV/m) in air at atmospheric pressure. 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

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Arc discharge - (electric arc) a discharge in a gas that occurs at atmospheric pressure and a small potential difference between closely spaced electrodes, but the current strength in the electric arc reaches tens of amperes. Application: spotlight, electric welding, cutting refractory metals.
Types of self-discharge

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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.

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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.

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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

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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.

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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.

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Scheme

Drawings that show methods of connecting electrical devices into a circuit are called diagrams. Figure a) shows an example of an electrical circuit.

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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.

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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.

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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.

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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.

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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.

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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

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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.

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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.

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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.

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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.

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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.

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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...

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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.

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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.

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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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Presentation on the topic: Electric current in conductors

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LESSON No. 1 TOPIC: ELECTRIC CURRENT. OBJECTIVES: 1. Repetition, deepening and assimilation of new knowledge on the topic “Electric current”. 2. Development of analytical and synthesizing thinking. 3. Fostering motives for learning and a positive attitude towards knowledge. TYPE OF LESSON: Lesson on learning new material. TYPE OF LESSON: Dialogue-communication. EQUIPMENT: Laboratory kit for measuring current in a circuit

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H O D U R O K A. I Organizational moment: 1. Statement of the topic and goals of the lesson. 2. Basic concepts: Types of interaction. Electromagnetic interaction. Electric charges. Electric field its properties and characteristics. Electric field work. Electric field energy. Electricity. Movement of charges in a conductor. Direction of electric current. Current strength. Current strength from the point of view of MKT. Constant electric current.

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II Survey (frontal): Types of interaction. Electromagnetic interaction. Electric charges. Electrical interaction charges. Stable and unstable systems of electric charges. Electric field. Properties of the electric field. Characteristics of the electric field. Electric field work. Electric field energy. Electricity.

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3. What are the main features, properties, structure of the field of moving charges? A moving electric charge is the source of an electromagnetic field; vortex field; the power lines are closed. The structure of the electromagnetic field of a dipole performing harmonic oscillations.

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3. What does current strength indicate? 4. Current strength as a physical quantity. 5. How do you choose the direction of electric current? 6. How is current measured? 7. What is called direct electric current? 8. What device measures current strength? What do you know about this device? 9. Assemble the circuit and measure the current in the circuit. A The quantitative measure of electric current is the current strength I - a scalar physical quantity equal to the ratio of the charge Δq transferred through the cross section of the conductor (Fig. 1.8.1) over the time interval Δt to this time interval. The direction of the electric current is taken to be the direction of movement of positive free charges. Current strength is measured in amperes - “A”. Ampere is the basic unit of measurement. A = C/s If the strength of the current and its direction do not change over time, then such a current is called constant.

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12. Where is direct electric current used? 10. We have already compared the intensity of the movement of charged particles in the conductor with the intensity of the movement of cars through a checkpoint on the highway. What characterizes the intensity of the directional movement of charged particles in a conductor? Δq = qN; N=nV = nSΔl; I = qnSvΔt/Δt. I = qnSv Intensity characterizes the magnitude of the electric charge passing through the cross section of the conductor in 1 s, or the strength of the current. 11. How to calculate the current strength from the point of view of MKT? Current strength from the point of view of MKT: I=Δq/Δt; slide no. 10

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VI Test of learning. The movement of electrons in a metal conductor placed in an electric field A is chaotic thermal, B is ordered in the direction of the electric field strength, C is the result of the superposition of the ordered movement of electrons on the chaotic thermal field, D coincides with the direction of the electric current in the conductor. 2. In what units is current measured? A – Cl, B – Cl/s, C – Cl s, D – A. 3. What does the current strength in a conductor depend on? A – on the amount of charge, its speed, concentration and cross-sectional area of ​​the conductor, B – on the amount of charge, its speed, concentration and length of the conductor, C – on the amount of charge passing through the cross-section of the conductor and the time of its passage, D – on voltage at the ends of the conductor and the resistance of the conductor. (Option 1 is done, option 2 is checked with red paste). The work is completed within 5 minutes (4+1) and submitted to the teacher.

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VI Reflection. 1. The movement of electrons in a metal conductor placed in an electric field B is the result of the superposition of the ordered movement of electrons on the chaotic thermal one. 2. In what units is current measured? B – C/s, D – A. 3. What determines the current strength in a conductor? A – on the magnitude of the charge, its speed, concentration and cross-sectional area of ​​the conductor, B – on the magnitude of the charge passing through the cross-section of the conductor and the time of its passage, D – on the voltage at the ends of the conductor and the resistance of the conductor. VII Summing up.

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Direct electric current

Electric current is the ordered (directed) movement of charged particles.

Electric current is the ordered movement of charged particles. For the existence of electric current, the following conditions are necessary: ​​The presence of free electrical charges in the conductor; The presence of an external electric field for the conductor.

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. I= I - current strength (A) q- electric charge (C) t- time (s) g t

Current unit -7

Ampere Andre Marie Born on January 22, 1775 in Polemiers near Lyon into an aristocratic family. He received a home education. He was engaged in research into the connection between electricity and magnetism (Ampère called this range of phenomena electrodynamics). Subsequently he developed the theory of magnetism. Ampère died in Marseille on June 10, 1836.

Ammeter Ammeter is a device for measuring current. The ammeter is connected in series with the device in which the current is measured.

APPLICATION OF ELECTRIC CURRENT

Biological effect of current

Thermal effect of current

The chemical effect of electric current was first discovered in 1800.

Chemical effect of current

Magnetic effect of current

Magnetic effect of current

Compare the experiments carried out in the figures. What do the experiences have in common and how are they different? A current source is a device in which some type of energy is converted into electrical energy. Devices that separate charges, i.e. creating an electric field are called current sources.

The first electric battery appeared in 1799. It was invented by the Italian physicist Alessandro Volta (1745 - 1827) - Italian physicist, chemist and physiologist, inventor of a source of direct electric current. His first current source, the “voltaic column,” was built in strict accordance with his theory of “metallic” electricity. Volta alternately placed several dozen small zinc and silver circles on top of each other, placing paper moistened with salted water between them.

Mechanical current source - mechanical energy is converted into electrical energy. Until the end of the 18th century, all technical current sources were based on electrification by friction. The most effective of these sources has become the electrophore machine (the machine's disks are rotated in opposite directions. As a result of the friction of the brushes on the disks, charges of the opposite sign accumulate on the machine's conductors) Electrophore machine

Thermal current source - internal energy is converted into electrical energy Thermocouple Thermocouple (thermocouple) - two wires from different metals must be soldered at one end, then the junction point is heated, then a current arises in them. The charges are separated when the junction is heated. Thermal elements are used in temperature sensors and in geothermal power plants as a temperature sensor. Thermocouple

Light energy is converted into electrical energy using solar panels. Solar battery Photocell. When some substances are illuminated with light, a current appears in them; light energy is converted into electrical energy. In this device, charges are separated under the influence of light. Solar batteries are made from photocells. They are used in solar batteries, light sensors, calculators, and video cameras. Photocell

Electromechanical generator. Charges are separated by performing mechanical work. Used for the production of industrial electricity. Electromechanical generator Generator (from Latin generator - manufacturer) is a device, apparatus or machine that produces any product.

Rice. 1 Fig. 2 Fig. 3 What current sources do you see in the pictures?

Design of a galvanic cell A galvanic cell is a chemical current source in which electrical energy is generated as a result of the direct conversion of chemical energy by an oxidation-reduction reaction.

A battery can be made from several galvanic cells.

A battery (from Latin accumulator - collector) is a device for storing energy for the purpose of its subsequent use.

Current source Method of charge separation Application Photocell Action of light Solar batteries Thermoelement Heating of junctions Temperature measurement Electromechanical generator Performing mechanical work Production of industrial electricity. energy Galvanic cell Chemical reaction Flashlights, radios Battery Chemical reaction Cars Classification of current sources

What is electric current called? (Electric current is the orderly movement of charged particles.) 2. What can cause charged particles to move in an orderly manner? (Electric field.) 3. How can an electric field be created? (With the help of electrification.) 4. Can a spark generated in an electrophore machine be called an electric current? (Yes, since there is a short-term ordered movement of charged particles?) Fixing the material. Questions:

5. What are the positive and negative poles of a current source? 6. What current sources do you know? 7. Does an electric current occur when a charged metal ball is grounded? 8. Do charged particles move in a conductor when current flows through it? 9. If you take a potato or an apple and stick copper and zinc plates into them. Then connect a 1.5V light bulb to these plates. What will you do? Fixing the material. Questions:

We solve problem 5.2 in class Page 27

For the experiment you will need: A durable paper towel; food foil; scissors; copper coins; salt; water; two insulated copper wires; small light bulb (1.5 V). Your actions: Dissolve a little salt in water; Carefully cut the paper towel and foil into squares slightly larger than coins; Soak the paper squares in salt water; Place a stack on top of each other: a copper coin, a piece of foil, another coin, and so on several times. There should be paper on top of the stack and a coin at the bottom. Slide the protected end of one wire under the stack, and connect the other end to the light bulb. Place one end of the second wire on top of the stack, and also connect the other to the light bulb. What happened? Home project. Make a battery.

Resources and literature used: Kabardin O.F. Physics, 8th grade M.: Prosveshchenie, 2014. Tomilin A.N. Stories about electricity. http://ru.wikipedia.org http:// www.disel.r u http:// www.fizika.ru http:// www.edu.doal.ru http:// schools.mari-el.ru http :// www.iro.yar.ru Homework: § 5,6,7 page 27, task No. 5.1; Home project. Make a battery (instructions are given to each student).