Electric current The project of a student of the 8th grade of the Municipal Educational Institution "Secondary School No. 4" of Kimry Ustinov Ilya 201 4-2015

An electric current is an ordered (directed) movement of charged particles.

The current strength is equal to the ratio electric charge q passing through the cross section of the conductor, by the time of its passage t. I \u003d I - current strength (A) q- electric charge (C) t- time (s) g t

Unit of measurement of current strength The unit of current strength is the current strength at which segments of parallel conductors 1 m long interact with a force of 2∙10 -7 N (0.0000002N). This unit is called AMP (A). -7

Ampère André Marie was born on January 22, 1775 in Polemiers near Lyon into an aristocratic family. He was educated at home. He studied the connection between electricity and magnetism (Ampère called this circle of phenomena electrodynamics). Subsequently, he developed the theory of magnetism. Ampère died in Marseille on June 10, 1836.

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

Current measurement Electrical circuit Electrical circuit diagram

Voltage is a physical quantity that shows how much work an electric field does when moving a unit positive charge from one point to another. AqU=

The unit of measurement is such an electrical voltage at the ends of the conductor, at which the work of moving an electric charge of 1 C along this conductor is 1 J. This unit is called VOLT (V)

Alessandro Volta is an Italian physicist, chemist and physiologist, one of the founders of the theory of electricity. Alessandro Volta was born in 1745, was the fourth child in the family. In 1801 he received the title of count and senator from Napoleon. Volta died in Como on March 5, 1827.

Voltmeter A voltmeter is a device for measuring electrical voltage. The voltmeter is connected to the circuit in parallel with that section of the circuit between the ends of which the voltage is measured.

Voltage measurement Electrical circuit diagram Electrical circuit

Electrical resistance Resistance is directly proportional to the length of the conductor, inversely proportional to its cross-sectional area and depends on the substance of the conductor. R = ρ ℓ S R- resistance ρ - resistivity ℓ - conductor length S- cross-sectional area

The reason for the resistance is the interaction of moving electrons with the ions of the crystal lattice.

The unit of resistance is 1 ohm. the resistance of such a conductor in which, at a voltage at the ends of 1 volt, the current strength is exactly 1 ampere.

Ohm Georg OM (Ohm) Georg Simon (March 16, 1787, Erlangen - July 6, 1854, Munich), a German physicist, author of one of the fundamental laws, Ohm took up the study of electricity. In 1852 Om received the post of ordinary professor. Ohm died on July 6, 1854. In 1881, at the Electrotechnical Congress in Paris, scientists unanimously approved the name of the unit of resistance - 1 Ohm.

Ohm's law The current strength in a section of a circuit is directly proportional to the voltage at the ends of this section and inversely proportional to its resistance. I = uR

Determination of conductor resistance R=U:I Measurement of current and voltage Electrical circuit diagram

APPLICATION OF ELECTRIC CURRENT

Presentation on physics on the topic: "Electric current" Completed by: Viktor_Sad Kapustin Lyceum No. 18; 10th grade Teacher I.A. Boyarina 1. Initial information about electric current 2. Current strength 3. Resistance 4. Voltage 5. Ohm's law for a circuit section 6. Ohm's law for a complete circuit 7. Connecting an ammeter and voltmeter 8. Tests

Electric current is the ordered movement of free electric charges under the action of electric field. Experience will help us understand this... To the top...

Current strength. The current strength is a physical quantity showing the charge passing through the conductor per unit of time. Mathematically, this definition is written as a formula: I - current strength (A) q - charge (C) t - time (s) To measure the current strength, a special device is used - an ammeter. It is included in the open circuit in the place where you need to measure the current strength. The unit of current strength... Back to top...

Resistance. 1. The main electrical characteristic of a conductor is resistance. 2. The resistance depends on the material of the conductor and its geometric dimensions: R = ? *(?/s) where? - specific resistance of the conductor (a value depending on the type of substance and its state). The unit of resistivity is 1 ohm * m. This is in short. Now more... Back to top...

Voltage. Voltage - potential difference between 2 points of the electrical circuit; in a section of a circuit that does not contain an electromotive force is equal to the product of the current strength and the resistance of the section. U = I * R Back to the top... That's it in a nutshell. Now more...

Ohm's law for a circuit section: The current strength in a circuit section is directly proportional to the voltage at the ends of the conductor and inversely proportional to its resistance. I=U/R To the beginning... And to prove?!

Ohm's law for a complete circuit: The current in a complete circuit is equal to the ratio of the EMF of the circuit to its impedance. I=? / (R + r), where? - EMF, and (R + r) - the total resistance of the circuit (the sum of the resistances of the external and internal sections of the circuit). Back to top... More details...

Connecting an ammeter and voltmeter: The ammeter is connected in series with the conductor in which the current is measured. The voltmeter is connected in parallel with the conductor on which the voltage is measured. R R Back to top...

An experiment explaining the definition of electric current: Two electrometers with large balls are placed at some distance from each other. One of them is electrified with a charged stick, which can be seen from the deflection of the arrow. Then a conductor is taken by the insulating handle, in the middle of which a neon light bulb is soldered. Connect the electrified ball to the non-electrified one. The light bulb flickers for a moment. According to the deviations of the arrows on the electrometers, they come to the conclusion: the left ball loses part of its charge, and the right one acquires the same charge. Explain... Back to top...

Let's think about what happens in this experiment: Since the charge of one ball decreased and the charge of the other increased, this means that electric charges passed through the conductor that connected the balls, which was accompanied by the glow of a light bulb. In this case, we say that the conductor flows electricity. What causes charges to move along a conductor? There can be only one answer - an electric field. Any current source has two poles, one pole is positively charged, the other is negatively charged. When a current source is operating, an electric field is created between its poles. When a conductor is connected to these poles, an electric field is also created in it, created by a current source. Under the influence of this electric field, free charges inside the conductor begin to move along the conductor from one pole to another. There is an ordered movement of electric charges. This is the electric current. If the conductor is disconnected from the current source, then the electric current stops. Back to top...

The unit of current strength is 1 ampere (1 A \u003d 1 C / s). The unit of current strength is 1 ampere (1 A \u003d 1 C / s). To establish this unit, the magnetic action of the current is used. It turns out that conductors carrying parallel currents in the same direction attract each other. This attraction is the stronger, the longer the length of these conductors and the smaller the distance between them. For 1 ampere, the strength of such a current is taken, which causes between two thin infinitely long parallel conductors located in vacuum at a distance of 1 m from each other, an attraction with a force of 0.0000002 N for each meter of their length. And on the right you see an ammeter: Back to top...

We will assemble a circuit from a light bulb and a current source. When the circuit is closed, the light will, of course, light up. Let us now include a piece of steel wire in the chain. The light bulb will become dimmer. Now let's replace the steel wire with nickel. The incandescence of the bulb spiral will decrease even more. In other words, we observed a weakening of the thermal effect of the current or a decrease in the power of the current. The conclusion follows from experience: an additional conductor, connected in series in the circuit, reduces the current strength in it. In other words, a conductor resists current. Different conductors (pieces of wire) have different resistance to current. So, the resistance of a conductor depends on the kind of substance from which this conductor is made. To the top... Are there other reasons that affect the resistance of the conductor?

Consider the experience shown in the figure. The letters A and B indicate the ends of the thin nickel wire, and the letter K indicates the moving contact. By moving it along the wire, we change the length of that part of it that is included in the chain (section AK). By moving contact K to the left, we will see that the bulb will burn brighter. Moving the contact to the right will make the bulb dim. From this experience it follows that a change in the length of a conductor included in a circuit leads to a change in its resistance. To the top... And what are the devices for changing the length of the conductor?

There are special devices - rheostats. The principle of their operation is the same as in the experiment we have considered with the wire. The only difference is that to reduce the size of the rheostat, the wire is wound on a porcelain cylinder fixed in the case, and the movable contact (they say: "engine" or "slider") is mounted on a metal rod, which simultaneously serves as a conductor. So, a rheostat is an electrical device whose resistance can be changed. Rheostats are used to regulate the current in the circuit. And the third reason that affects the resistance of the conductor is its cross-sectional area. As it increases, the resistance of the conductor decreases. The resistance of conductors also changes as their temperature changes. Back to top...

The same current passes through both bulbs: 0.4 A. But the large lamp burns brighter, that is, it works with more power than the small one. It turns out that the power can be different for the same current strength? In our case, the voltage generated by the rectifier is less than the voltage generated by the city power grid. Therefore, when the current strength is equal, the current power in the circuit with a lower voltage is less. By international agreement, the unit of electrical voltage is 1 volt. This is a voltage that, at a current strength of 1 A, creates a current of 1 W. To the beginning ... Wol - this is understandable. We all know 220 V, which should not be touched. But how to measure these 220?

To measure voltage, a special device is used - a voltmeter. It is always connected in parallel to the ends of the section of the circuit where the voltage is to be measured. Appearance school demonstration voltmeter is shown in the figure on the right. Back to top...

Let's establish what is the dependence of the current on the voltage, by experience: The figure shows an electrical circuit consisting of a current source - a battery, an ammeter, a nickel wire spiral, a key and a voltmeter connected in parallel to the spiral. Close the circuit and note the instrument readings. Then a second battery of the same type is connected to the first battery and the circuit is closed again. In this case, the voltage on the spiral will double, and the ammeter will show twice the current. With three batteries, the voltage on the spiral increases three times, and the current strength increases by the same amount. Thus, experience shows that how many times the voltage applied to the same conductor increases, the current strength in it increases by the same amount. In other words, the current in a conductor is directly proportional to the voltage at the ends of the conductor. Well, then ... You can go to the beginning ...

To answer the question of how the current strength in the circuit depends on the resistance, let's turn to experience. The figure shows an electrical circuit in which the current source is a battery. In this circuit, conductors with different resistances are included in turn. The voltage at the ends of the conductor during the experiment is maintained constant. This is monitored by the readings of the voltmeter. The current in the circuit is measured with an ammeter. The table below shows the results of experiments with three different conductors: Continue experiment... Back to top...

In the first experiment, the resistance of the conductor is 1 ohm and the current in the circuit is 2 A. The resistance of the second conductor is 2 ohms, i.e. twice as much, and the current strength is half as much. And finally, in the third case, the resistance of the circuit increased four times and the current strength decreased by the same amount. Recall that the voltage at the ends of the conductors in all three experiments was the same, equal to 2 V. Summarizing the results of the experiments, we conclude that the current strength in the conductor is inversely proportional to the resistance of the conductor. Let's express our two experiences in graphs: To the beginning...

The inner section of the circuit, like the outer one, has some resistance to the current passing through it. It is called the internal resistance of the source. For example, the internal resistance of the generator is due to the resistance of the windings, and the internal resistance of the galvanic cells is due to the resistance of the electrolyte and electrodes. Consider the simplest electrical circuit consisting of a current source and resistance in an external circuit. The internal section of the circuit, located inside the current source, as well as the external one, has electrical resistance. We will denote the resistance of the outer section of the circuit through R, and the resistance of the inner section through r. To the beginning... Continue...

And how did Om derive his law for a complete circuit: EMF in closed circuit is equal to the sum of the voltage drops in the external and internal sections. Let us write, according to Ohm's law, expressions for the voltages in the external and internal chain sections.Adding the expressions obtained, and expressing the current strength from the resulting equality, we obtain a formula that reflects Ohm's law for a complete circuit. Back to top...

Tests: 1. The figure shows the scale of an ammeter included in an electrical circuit. What is the current in the circuit? A. 12 ± 1 A B. 18 ± 2 A C. 14 ± 2 A 2. A proton flies into the space between two charged bars. What trajectory will he follow? A. 1 B. 2 C. 3 D. 4 different meanings voltage at its terminals. The measurement results are shown in the figure. What, most likely, was the value of the current in the device at a voltage of 0 V? A. 0 mA B. 5 mA D. 10 mA Back to top...

The answer is not correct... Bad tests... I want to start... This, of course, is sad, but can we try again?!

Bravo!!! It's right!!! Too easy for me... So let's get started... I love this game! Let's repeat!!!

slide 1

Lecture plan 1. The concept of conduction current. Current vector and current strength. 2. Differential form of Ohm's law. 3. Series 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, charged particles. If an electric field is created in the conductor, then free electric charges will move in it - a current arises, called the 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


It is customary to take the direction of movement of positive charges as the direction of current. For the emergence and existence of current, it is necessary: ​​1. the presence of free charged particles; 2. the presence of an electric field in the conductor. The main characteristic of the current is the strength of the current, which is equal to the amount of charge that has passed in 1 second through the cross section of the conductor. Where q is the amount of charge; t is the charge passage time; The current strength is a scalar value.

slide 4


The electric current over the surface of the conductor can be unevenly distributed, therefore, in some cases, the concept of current density j is used. The average current density is equal to the ratio of the current strength to the cross-sectional area of ​​the conductor. Where j is the current change; S - area change.

slide 5


current density

slide 6


In 1826, the German physicist Ohm experimentally established that the current strength J in the conductor is directly proportional to the voltage U between its ends Where k is the coefficient of proportionality, called electrical conductivity or conductivity; [k] = [cm] (siemens). The value 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 7


We express from this formula R The 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 the cross-sectional area S Where  - characterizes the material from which the conductor is made and is called the resistivity of the conductor.

Slide 8


We express : The resistance of the conductor depends on the temperature. With increasing temperature, the resistance increases Where R0 is the resistance of the conductor at 0С; t - temperature;  - temperature coefficient of resistance (for metal  0.04 deg-1). The formula is also valid for resistivity Where0 is the resistivity of the conductor at 0С.

Slide 9


At low temperatures (

Slide 10


Let's regroup the terms of the expression Where I/S=j is the current density; 1/= - specific conductivity of the conductor substance; U / l \u003d E - electric field strength in the conductor. Ohm's law in differential form.

slide 11


Ohm's law for a homogeneous section of a chain. Differential form of Ohm's law.

slide 12

3. Series and parallel connection of conductors

Serial 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 13


Parallel connection conductors U=const I=I1+I2+I3 U1=U2=U R1 R2 R3 For N identical conductors

Slide 14


4. The reason for the appearance of electric current in the conductor. The physical meaning of the concept of external forces To maintain a constant current in the circuit, it is necessary to separate positive and negative charges in the current source, for this, forces of non-electric origin, called external forces, must act on free charges. Due to the field created by external forces, electric charges move inside the current source against the forces of the electrostatic field.

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. External forces cause separation of opposite charges and maintain a potential difference at the ends of the conductor. An additional electric field of external forces in the conductor is created by current sources (galvanic cells, batteries, electric generators).

slide 16


EMF of the current source The physical quantity equal to the work of external forces to move a unit positive charge between the poles of the source is called the electromotive force of the current source (EMF).

Slide 17


Ohm's law for an inhomogeneous chain section

Slide 18

5. Derivation of Ohm's law for a closed electrical circuit

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 is the internal resistance. where is the voltage across the external resistance; A - work on moving the charge q inside the current source, i.e. work on the internal resistance.

Slide 19


Then since, then we rewrite the expression for : , Since according to Ohm's law for a closed electrical circuit (=IR) IR and Ir are the voltage drop in the external and internal sections of the circuit,

Slide 20


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.

slide 21


6. The first and second Kirchhoff's rules The first Kirchhoff's rule is the condition of constant current in the circuit. The algebraic sum of the current strengths in the branching node is equal to zero where n is the number of conductors; Ii - currents in conductors. The currents approaching the node are considered positive, leaving the node - negative. For node A, the first Kirchhoff rule is written:

slide 22


Kirchhoff's first rule A node in an electrical circuit is a point at which at least three conductors converge. The sum of the currents converging in the node is equal to zero - the first rule of Kirchhoff. Kirchhoff's first rule is a consequence of the law of conservation of charge - an electric charge cannot accumulate in a node.

slide 23


Kirchhoff's second rule Kirchhoff's second rule is a consequence of the law of conservation of energy. In any closed circuit of a branched electric circuit, the algebraic sum Ii for the resistances Ri of the corresponding sections of this circuit is equal to the sum of the EMF i applied in it

slide 24


Kirchhoff's second rule

Slide 25


To draw up an equation, you must choose the direction of the bypass (clockwise or counterclockwise). All currents coinciding in direction with the loop bypass are considered positive. The EMF of current sources is considered positive if they create a current directed towards the bypass of the circuit. So, for example, the Kirchhoff rule for I, II, III cl. I3R3 = – 1 + 3 Based on these equations, circuits are calculated.

slide 26


7. Contact potential difference. Thermoelectric phenomena Electrons with the highest 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. Between the electron gas in the metal and the "electron cloud" there is a dynamic equilibrium. The work function of an electron is the work that must be done to remove an electron from a metal into a vacuum. The surface of the metal is an electrical double layer, similar to a very thin capacitor.

Slide 27


The potential difference between the plates of the capacitor depends on the work function of the electron. Wheree is the electron charge;  - contact potential difference between the metal and the environment; A is the work function (electron-volt - E-V). The work function depends on the chemical nature of the metal and the state of its surface (contamination, moisture).

Slide 28


Volta's laws: 1. When connecting two conductors made of different metals, 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 series-connected metal conductors at the same temperature does not depend on the chemical composition of the intermediate conductors. It is equal to the contact potential difference arising from the direct connection of the extreme conductors.

Slide 29


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 the closed circuit, which is directly proportional to the temperature difference between the two 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 the medium whose temperature T1 is to be measured, and the second junction is placed in the medium with a constant known temperature. Thermocouples have a number of advantages over conventional thermometers: they allow measuring temperatures in a wide range from tens to thousands of degrees of the absolute scale.

Slide 31


Gases under normal conditions are dielectricsR=>∞, they consist of electrically neutral atoms and molecules. When gases are ionized, electric current carriers arise ( positive charges). Electric current in gases is called a gas discharge. To carry out a gas discharge to a tube with ionized gas, there must be an electric or magnetic field.

slide 32


Gas ionization is the decay of a neutral atom into a positive ion and an electron under the action of an ionizer (external influences - strong heating, ultraviolet and X-rays, radioactive radiation, when atoms (molecules) of gases are bombarded by fast electrons or ions). Ion electron atom neutral

Slide 33


The measure of the ionization process is the intensity of ionization, measured by the number of pairs of oppositely charged particles that appear in a unit volume of gas in a unit period of time. Impact ionization is the detachment from an atom (molecule) of one or more electrons, caused by a collision with atoms or molecules of a gas of electrons or ions accelerated by an electric field in a discharge.

slide 34


Recombination is the union of an electron with an ion to form a neutral atom. If the action of the ionizer stops, the gas again becomes a dialectic. electron ion

Slide 35


1. A non-self-sustaining gas discharge is a discharge that exists only under the action of external ionizers. Current-voltage characteristic of a gas discharge: as U increases, the number of charged particles reaching the electrode increases and the current increases to I \u003d 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 univalent ions formed in the gas volume in 1 s.

slide 36


2. Independent gas discharge - a discharge in a gas that persists after the termination of the external ionizer. It is maintained and developed by impact ionization. The non-self-sustained gas discharge becomes independent at Uz - ignition voltage. The process of such a transition is called electrical breakdown of the gas. Distinguish:

Slide 37


Corona discharge - occurs at high pressure and in a sharply inhomogeneous field with a large curvature of the surface, is used in the disinfection of crop seeds. Glow discharge - occurs at low pressures, is used in gas-light tubes, gas lasers. Spark discharge - at P = Ratm and at high electric fields - lightning (currents up to several thousand Amperes, length - several kilometers). Arc discharge - occurs between closely shifted electrodes, (T \u003d 3000 ° C - at atmospheric pressure. Used as a light source in powerful spotlights, in projection equipment.

Slide 38


Plasma is a special aggregate state of matter, characterized by a high degree of ionization of its particles. Plasma is subdivided 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 discharge lamps, plasma sources of electrical energy, magnetodynamic generators.

Slide 39


Emission phenomena: 1. Photoelectronic emission - pulling out under the action of light of electrons from the surface of metals in a vacuum. 2. Thermionic emission - the emission of electrons by solid or liquid bodies when they are heated. 3. Secondary electron emission - a counter flow of electrons from a surface bombarded by electrons in a vacuum. Devices based on the phenomenon of thermionic emission are called vacuum tubes.

Slide 40


In solids, an electron interacts not only with its own atom, but also with other atoms of the crystal lattice, the energy levels of atoms are split with the formation of an energy band. The energy of these electrons can be within the shaded areas, called allowed energy bands. Discrete levels are separated by areas of forbidden energy values ​​- forbidden zones (their width is commensurate with the width of the forbidden zones). Differences in electrical properties various types solids is explained by: 1) the width of the forbidden energy bands; 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 action 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


The electric field is created in the liquid by electrodes (“+” – anode, “–” – cathode). Positive ions (cations) move towards the cathode, negative - towards the anode. The appearance of ions in electrolytes is explained by electrical dissociation - the disintegration of solute molecules into positive and negative ions as a result of interaction with a 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 motion of ions, the reverse process of ion reunification occurs, called recombination.

slide 43


Laws of M. Faraday (1834). 1. The mass of the substance released on the electrode is directly proportional to the electric charge q passed through the electrolyte or Where k is the electrochemical equivalent of the substance; is equal to the mass of the substance released during the passage of a unit amount of electricity through the electrolyte. Where I - D.C. passing through the electrolyte.

Slide 46


THANK YOU FOR YOUR ATTENTION

View all slides

slide 2

Electric current is called the ordered movement of charged particles. To get an electric current in a conductor, it is necessary to create an electric field in it. Under the action of this field, charged particles that can move freely in this conductor will begin to move in the direction of the action of electric forces on them. An electric current arises. In order for the electric current to exist in the conductor for a long time, it is necessary to maintain an electric field in it all this time. The electric field in the conductors is created and can be maintained for a long time by sources of electric current.

slide 3

Current source poles

Current sources are different, but in each of them work is done to separate positively and negatively charged particles. Separated particles accumulate at the poles of the current source. This is the name of the place to which conductors are connected using terminals or clamps. One pole of the current source is charged positively, and the other is negatively charged.

slide 4

Current sources

In current sources, in the course of work on the separation of charged particles, mechanical work is converted into electrical work. So, for example, in an electrophore machine (see fig.), mechanical energy is converted into electrical energy

slide 5

Electrical circuit and its components

In order to use the energy of an electric current, you must first have a current source. Electric motors, lamps, tiles, all kinds of household appliances are called receivers or consumers of electrical energy.

slide 6

Symbols used in the 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, use keys, switches, buttons, switches. A current source, receivers, closing devices, interconnected by wires, make up the simplest electrical circuit. In order for there to be current in the circuit, it must be closed. If the wire breaks in any place, the current in the circuit will stop.

Slide 7

Scheme

Drawings that show how to connect electrical devices in 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 an ordered movement of free electrons. The proof that the current in metals is due to electrons was the experiments of physicists from our country L.I. Mendelstam 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 crystal lattice of the metal, and free electrons move in the space between them, i.e., not connected with the nuclei of their atoms (see Fig.). 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 an 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 order.

slide 11

The movement of electrons is partially reminiscent of the drift of ice floes during an ice drift ...

When they, moving randomly and colliding with each other, drift along the river. The ordered movement of conduction electrons is an electric current in metals.

slide 12

The action of electric current.

We can judge the presence of an electric current in a circuit only by the various phenomena that an electric current causes. Such phenomena are called action current. Some of these actions are easy to observe in practice.

slide 13

The thermal effect of the current ...

... can be observed, for example, by connecting an iron or nickel wire to the poles of a current source. At the same time, the wire heats up and, having lengthened, slightly sags. It can even be red-hot. IN electric lamps, for example, a thin tungsten wire is heated by a current and a bright glow

Slide 14

The chemical action of the current ...

... consists in the fact that in some solutions of acids, when an electric current passes through them, a release of substances is observed. The substances contained in the solution are deposited on the electrodes dipped into this solution. For example, when a current is passed through a solution of copper sulphate, pure copper will be released on a negatively charged electrode. This is used to obtain pure metals.

slide 15

The magnetic action of the current ...

… can also be observed in experience. For this copper wire, covered with insulating material, must be wound on an iron nail, and the ends of the wire connected to a current source. When the circuit is closed, the nail becomes a magnet and attracts small iron objects: nails, iron shavings, sawdust. With the disappearance of current in the winding, the nail is demagnetized.

slide 16

Consider now the interaction between a current-carrying conductor and a magnet.

The figure shows a small frame hanging on threads, on which several turns of thin copper wire. The ends of the winding are connected to the poles of the current source. Therefore, 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, then it will rotate.

Slide 17

The direction of the electric current.

Since in most cases we are dealing with an electric current in metals, it would be reasonable to take the direction of the movement of electrons in an electric field as the direction of the current in the circuit, i.e. consider that the current is directed from the negative pole of the source to the positive. For the direction of the current, we conditionally took 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 1s determines the strength of the current in the circuit. This means that the current strength is equal to the ratio of the electric charge q that has passed through the cross section of the conductor to the time of its passage t. Where I is the current strength.

Slide 19

Experience in the interaction of two conductors with current.

On International Conference according to weights and measures in 1948, it was decided to base the definition of the unit of current strength on the phenomenon of the interaction of two conductors with current. Let's first get acquainted with this phenomenon in experience ...

Slide 20

Experience

The figure shows two flexible straight conductors parallel to each other. Both conductors are connected to a current source. When the 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 of conductors with current can be measured, it depends on the length of the conductor, the distance between them, the environment in which the conductors are located, on the strength of the current in the conductors.

slide 21

Units of current.

The unit of current strength is the current strength at which segments of such parallel conductors 1 m long interact with a force of 0.0000002 N. This unit of current strength is called an ampere (A). Since it is named after the French scientist Andre Ampère.

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 number 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 very important characteristic electrical circuit. Working with electrical circuits need to know what to human body current strength up to 1 Ma is considered safe. Current strength greater than 100 mA leads to serious damage to the body.

View all slides

1 of 12

Presentation on the topic: Electric current in conductors

slide number 1

Description of the slide:

slide number 2

Description of the slide:

LESSON #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. Education of motives for learning, a positive attitude towards knowledge. LESSON TYPE: Lesson learning new material. LESSON TYPE: Dialogue-communication. EQUIPMENT: laboratory kit for measuring current in a circuit

slide number 3

Description of the slide:

H O D U R O K A. I Organizational moment: 1. Presentation of the topic and objectives of the lesson. 2. Basic concepts: Types of interaction. Electromagnetic interaction. Electric charges. Electric field its properties and characteristics. The work of the electric field. Electric field energy. Electricity. Movement of charges in a conductor. The direction of the electric current. Current strength. Current strength in terms of MKT. Constant electric current.

slide number 4

Description of the slide:

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

slide number 5

Description of the slide:

slide number 6

Description of the slide:

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; lines of force are closed. The structure of the electromagnetic field of a dipole that performs harmonic oscillations.

slide number 7

Description of the slide:

3. What does the current strength show? 4. Current strength as a physical quantity. 5. How is the direction of the electric current chosen? 6. What is the current strength measured in? 7. What is called direct electric current? 8. What instrument measures the 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 the 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 movement of positive free charges is taken as the direction of the electric current. The current strength is measured in amperes - "A". The ampere is the basic unit of measurement. A \u003d Kl / s If the current strength and its direction do not change with time, then such a current is called constant.

slide number 8

Description of the slide:

12. Where is direct electric current used? 10. We have already compared the intensity of movement of charged particles in a conductor with the intensity of movement of cars through a checkpoint on a highway. What characterizes the intensity of the directed motion of charged particles in a conductor? ∆q = qN; N=nV = nSΔl; I = qnSvΔt/Δt. I \u003d qnSv The intensity characterizes the magnitude of the electric charge passing through the cross section of the conductor for a 1 s, or the strength of the current. 11. How to calculate the current strength in terms of MKT? Current strength from the point of view of the MKT: I \u003d Δq / Δt; Slide No. 10

Description of the slide:

VI Test for learning. The movement of electrons in a metal conductor placed in an electric field A - chaotic thermal, B - ordered in the direction of the electric field strength, C - is the result of superimposing the ordered movement of electrons, on a chaotic thermal one, D - coincides with the direction of the electric current in the conductor. 2. In what units is the current strength measured? A - C, B - Cl / s, C - Cl s, G - A. 3. What determines the current strength in the conductor? A - on the magnitude of the charge, its speed, concentration and cross-sectional area of ​​\u200b\u200bthe conductor, B - on the magnitude of the charge, its speed, concentration and length of the conductor, C - on the magnitude of the charge that has passed 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 performs, option 2 checks with red paste). Works are completed within 5 minutes (4+1) and submitted to the teacher.

slide number 11

Description of the slide:

VI Reflection. 1. The movement of electrons in a metal conductor placed in an electric field B - is the result of the imposition of an ordered movement of electrons on a chaotic thermal one. 2. In what units is the current strength measured? B - C / s, D - A. 3. What determines the current strength in the conductor? A - on the magnitude of the charge, its speed, concentration and cross-sectional area of ​​\u200b\u200bthe conductor, B - on the magnitude of the charge that has passed through the cross section of the conductor and the time of its passage, Г - on the voltage at the ends of the conductor and the resistance of the conductor. VII Summing up.

slide number 12

Description of the slide: