Presentation Permanent electric current. Permanent electric current concept about electric current. Consider now the interaction between the conductor with current and magnet
Electric current electric current - ordered (directional) movement of electrical charges. Current conductivity (current in conductors) - movement of micro-charged in the macker. Convection current is the movement of macroscopic charged bodies in space. Current in vacuo - movement of micro-charged in vacuum.
Electric current in the explorer Under the action of the applied electric field, free electric charges are moved: Positive - on the field, negative - against the field. The charge carriers make a complex movement: 1) chaotic with an average velocity V ~ (10 3 ÷ 10 4 m / s), 2) directed with an average velocity V ~ e (shares mm / s).
Thus, the average speed of the directional electron movement is much less than the average speed of their chaotic movement. A minor average rate of directional movement is explained by their frequent clashes with the ions of the crystal lattice. At the same time, any change in the electric field is transmitted along the wires at a rate equal to the velocity of the electromagnetic wave - (3 · 10 8 m / s). Therefore, the movement of electrons under the action of the external field occurs throughout the wire almost simultaneously with the signal supply.
When the charges are moved, their equilibrium distribution is disturbed. Consequently, the surface of the conductor is no longer equipotential and the vector of electric field tension E is not directed perpendicular to the surface, since for the movement of charges it is necessary that on the surface E τ 0. For this reason, there is an electric field for this reason inside the conductor, which is zero only in the case of equilibrium distribution charges on the surface of the conductor.
Conditions for the emergence and existence of conductivity current: 1. The presence of free charge carriers in the medium, i.e. Charged particles capable of moving. In the metal, these are electrons conduction; in electrolytes - positive and negative ions; Gas - positive, negative ions and electrons.
Conditions for the appearance and existence of conductivity current: 2. The presence of an electric field, the energy of which would be spent on the movement of electrical charges. In order for the current to be long, the energy of the electric field should be replenished all the time, i.e. We need an electrical source - a device in which there is a conversion of any energy into the energy of the electric field.
- The current is numerically equal to the charge passing through the cross section of the conductor per unit of time. In C:. The movement of the charge carriers of one sign is equivalent to the movement of carriers of the opposite sign in the opposite direction. If the current is created by two types of media:
Third-party. Electromotive force. Voltage If only the power of the electrostatic field is valid in the circuit on the current carrier, then the carriers are moved, which leads to the equalization of the potentials at all points of the chain and to the disappearance of the electric field. Therefore, for the existence of DC, it is necessary in the chain of the device, which creates and maintains the difference in potentials φ due to the work of non-electrical forces. Such devices are called current sources (generators - mechanical energy converted; batteries - the energy of the chemical reaction between the electrodes and the electrolyte).
Third-party. Electromotive force. Third-party forces of non-electric origin forces acting on charges from current sources. At the expense of the field of third-party power, electric charges are moving inside the current source against the power of the electrostatic field. Consequently, at the ends of the external chain, the potential difference is maintained and the circuit flows the constant current.
Third-party. Electromotive force. Third-party forces make work on the movement of electrical charges. Electrical power (EDs - E) - a physical value determined by the work performed by third-party forces when moving a single positive charge
Ohma law for a homogeneous section of the chain chain is called a circuit section that does not contain the source of E.D. Ohm's law in an integrated form: The current is directly proportional to the voltage drop on a homogeneous section of the chain and inversely proportional to the resistance of this site.
Ohm's law is not a universal connection between current and voltage. a) Current in gases and semiconductors is subject to Ohm's law only with small U. b) current in vacuo does not obey Ohm. Law of Boguslavsky-Langmür (Law 3/2): I ~ U 3/2. c) in an arc discharge - with increasing current, the voltage drops. Estimation of the law of Ohm is due to the dependence of the resistance from the current.
Ohm's law in SI resistance R is measured in Omah. The value of R depends on the shape and size of the conductor, as well as the properties of the material from which it is made. For a cylindrical conductor: where ρ is a specific electrical resistance [Ohm · M], for metals its value of about 10 -8 Ohm · m.
The conductor resistance depends on its temperature: α is the temperature coefficient of resistance, for pure metals (with not very low temperatures α 1/273 to -1, ρ 0, R 0 - respectively, the resistivity and resistance of the conductor at T \u003d 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, the directional movement of electrons is inhibited.
Ohm's law for an inhomogeneous section of the circuit inhomogeneous - section of the chain containing the source of EDs The closed circuit contains the source of ED, which in the 1-2 direction contributes to the movement of positive charges. E is the tension of the field of the Coulomb forces, the eta - the strength of the field of third-party forces.
Ohma law for an inhomogeneous section of the chain The work performed by the Coulomb and third-party forces to move the unit positive charge Q 0+ - the voltage drop (voltage). Since points 1, 2 were selected arbitrarily, then the obtained ratios are valid for any two points of the electrical circuit:
Operation and power of electric current The law of Joule-Lenz under the collision of free electrons with the ions of the crystal lattice, they transmit an excess of kinetic energy by ions, which is acquired during the accelerated movement in the electric field. As a result of these collisions, the amplitude of oscillations of ions near the nodes of the crystal lattice increases (the thermal motion of ions becomes more intense). Consequently, the conductor heats up: temperature - measure of the intensity of the chaotic movement of atoms and molecules. Allocated heat q is equal to operating current A.
Kirchhoff's laws are used to calculate the branched DC circuits. The unbranched electrical circuit is a circuit in which all the elements of the chain are connected in series. Electric circuit element - any device included in the electrical circuit. The electrical circuit assembly is the branched circuit point in which more than two conductors converge. The branched electrical circuit branch is a circuit section between two nodes.
The second law of Kirchhoff (Generalized Ohm Law): In any closed loop, an arbitrarily selected in the branched electrical circuit, the algebraic amount of the products of the current I I strengths on the resistance of the respective sections of the R i of this circuit is equal to the algebraic amount of ED. in the circuit.
The second law of Kirchhoff Current is considered positive if its direction coincides with the conditionally selected direction of circuit bypass. E.D.S. It is considered positive if the direction of the bypass occurs from - to + the source of the current, i.e. E.D.S. Creates a current that coincides with the direction of bypass.
The procedure for calculating the branched chain: 1. Arbitrarily select and designate the direction of current in all parts of the chain on the drawing. 2. Calculate the number of nodes in the chain (M). Record the first Kirchhoff law for each of the (M-1) nodes. 3. Allocate arbitrarily closed contours in the circuit, arbitrarily select contouring directions. 4. Record for contours the second law of Kirchoff. If the chain consists of p-branches and m-nodes, the number of independent equations of the 2nd Kirchhoff law is equal to (P-M + 1).
Electric current Draft student grade 8 of MOU "SS №4" Kimra Ustinova Ilya 201 4-2015
Electric current is called ordered (directional) movement of charged particles.
The strength of the current is equal to the ratio of the electrical charge Q, which passed through the cross section of the conductor, to the times of its passage t. I \u003d i-cyllace (a) Q- Electric charge (CL) T- Time (C) G T
The unit for measuring the current force per unit of current force takes strength of the current at which the segments of parallel conductors with a length of 1M interact with force 2 ∙ 10 -7 N (0.0000002H). This unit is called amp (a). -7.
Ampere Andre Marie was born on January 22, 1775 in the Polem near Lyon in the aristocratic family. Received home education .. Engaged in research of communication between electricity and magnetism (this circle of ampere phenomena called electrodynamics). Subsequently developed the theory of magnetism. Ampere died in Marseille on June 10, 1836.
Ampmeter ammeter-device for measuring current force. The ammeter is included in the chain sequentially with the instrument, the current strength in which is measured.
Current measurement electrical circuit circuit circuit
Voltage is a physical value that shows which work the electric field is performed when moving a single positive charge from one point to another. A Q U \u003d
The unit of measurement takes such an electrical voltage at the ends of the conductor, in which the work on the movement of the electric charge in 1 cl along this conductor is 1 J. This unit is called Volt (B)
Alessandro Voltage Italian physicist, chemist and physiologist, one of the founders of electricity doctrine. Alessandro Volta was born in 1745, was a fourth child in the family. In 1801 he received from Napoleon the title of Count and Senator. Died Volta in Como on March 5, 1827.
Voltmeter voltmeter device for measuring the electrical voltage. The voltmeter is included in the chain parallel to that section of the chain between the ends of which the voltage is measured.
Voltage measurement Electrical circuit circuit Electric circuit
Electrical resistance Resistance is directly proportional to the length of the conductor, inversely proportional to the area of \u200b\u200bits cross section and depends on the substance of the conductor. R \u003d ρ ℓ S R resistance ρ-effect resistance ℓ - Explorer length S- cross-sectional area
The cause of resistance is the interaction of moving electrons with the ions of the crystal lattice.
Per unit of resistance take 1 ohm. Resistance to such a conductor, in which at the ends at the ends of 1 volt, the current strength of the Roven 1 amper.
Om Georg Ohm (OHM) Georg Simon (March 16, 1787, Erlangen - July 6, 1854, Munich), a German physicist, the author of one of the main laws, was engaged in the research of electricity. In 1852, I 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 resistance unit 1 Ohm.
Ohm's law The strength of the current in the section of the chain is directly proportional to the voltage at the ends of this section and is inversely proportional to its resistance. I \u003d u r
Determination of the resistance of the conductor R \u003d U: I Measurement of current force and voltage circuit of the electrical circuit
Application of electric current
Slide 1.
Lecture Plan 1. Concept of conductivity current. TK vector and current. 2. Differential form of the Ohm law. 3. Sequential and parallel connection of the conductors. 4. The reason for the appearance of the electric field in the conductor, the physical meaning of the concept of third-party forces. 5. Conclusion of the Ohm Law for the entire chain. 6. The first and second rule of Kirchhoff. 7. Contact potential difference. Thermoelectric phenomena. 8. Electric current in various environments. 9. Current in fluids. Electrolysis. Faraday laws.
Slide 2.
Electric current is called an ordered movement of electrical charges. Current carriers may be electrons, ions, charged particles. If in the conductor to create an electric field, then there are free electrical charges in it - there is a current called conduction current. If the charged body is moved in space, the current is called convection. 1. The concept of conductivity current. Current vector and current
Slide 3.
For the direction of current it is customary to take the direction of movement of positive charges. For the occurrence and existence of current, it is necessary: \u200b\u200b1. The prerequisites of free charged particles; 2. The availability of the electric field in the explorer. The main characteristic of the current is the strength of the current, which is equal to the value of the charge, which passed in 1 second through the cross section of the conductor. Where q is the charge value; t - the time of charge; Current strength is scalar.
Slide 4.
The electric current on the surface of the conductor can be distributed unevenly, so in some cases the current density is used. The average current density is equal to the ratio of the current to the cross-sectional area of \u200b\u200bthe conductor. Where j is a change in current; S - Change area.
Slide 5.
Cone density
Slide 6.
In 1826, the German physicist ohm emphasized that the current 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] \u003d [cm] (Siemens). The value is called the electrical resistance of the conductor. Ohma law for a plot of an electrical circuit that does not contain current source 2. Differential form of the law of Oma
Slide 7.
Expressing from this formula R electrical resistance depends on the shape, size and substance of the conductor. The resistance of the conductor is directly proportional to its length L and inversely proportional to the cross-sectional area where - characterizes the material from which the conductor is made and is called the resistivity of the conductor.
Slide 8.
Express : The conductor resistance depends on temperature. With increasing temperature, the resistance increases wherer0 - the resistance of the conductor at 0 ° C; T - Temperature; - temperature resistance coefficient (for metal 0.04 grad-1). Formula is also valid for specific resistance where 0 - the resistivity of the conductor at 0.
Slide 9.
At low temperatures (
Slide 10.
Regroup member of the expression where I / S \u003d J- current density; 1 / \u003d - the specific conductivity of the substance of the conductor; U / L \u003d E - electric field strength in the explorer. Ohm's law in differential form.
Slide 11.
Ohm's law for a homogeneous section of the chain. Differential form of the law Ohm.
Slide 12.
3. Sequential and parallel conductor connection
Sequential compound of conductors I \u003d const (by the reduction of charge); U \u003d U1 + U2 RB \u003d R1 + R2 + R3 R1 + Ri R \u003d n * R1 (for n identical conductors) R1 R2 R3
Slide 13.
Parallel compound of conductors U \u003d const i \u003d i1 + i2 + i3 u1 \u003d u2 \u003d u R1 R2 R3 for n identical conductors
Slide 14.
4. Cause of electrical current in the conductor. The physical meaning of the concept of third-party forces to maintain direct current in the chain, it is necessary to separate positive and negative charges in the current source, for this, for free charges, the forces of non-electric origin, called third-party forces, must be operated. Due to the third-party fields, the electric charges are moving inside the current source against the power of the electrostatic field.
Slide 15.
Due to this, at the ends of the external circuit, the potential difference is maintained and a permanent electric current is maintained. Third-party forces cause the separation of multi-chain charges and maintain the difference in potentials at the ends of the conductor. The added electrical field of third-party power in the conductor is created by current sources (galvanic elements, batteries, electrical generators).
Slide 16.
EMF of the current source The physical value is equal to the work of third-party forces for the movement of a single positive charge between the source poles is called the electromotive power source (EMF).
Slide 17.
Status for the inhomogeneous section of the chain
Slide 18.
5. Conclusion of the Ohm law for a closed electrical circuit
Let a closed electrical circuit consists of a current source C , with an internal resistance of R and an outer part having resistance R. R - external resistance; R - internal resistance. where - the voltage on the external resistance; A - work on the movement of charge q inside the current source, i.e., work on internal resistance.
Slide 19.
Then, as, then we rewrite the expression for : because according to the Ohm law for a closed electrical circuit ( \u003d Ir) IR and IR - the voltage drop at the external and inner sections of the chain,
Slide 20.
Then -zakon Ohm for a closed electrical circuit in a closed electrical circuit The electromotive strength of the current source is equal to the sum of the voltage drops on all parts of the chain.
Slide 21.
6. The first and second Rules of Kirchhoff The first Kirchhoff rule is the condition for the constancy of the current in the chain. The algebraic sum of the strength of the current in the branching unit is zero where n is the number of conductors; II - Current in conductors. The currents suitable for the node are considered positive, leaving the node - negative. For the node and the first Rule of Kirchhoff will be recorded:
Slide 22.
The first Kirchhoff rule is called a point in which no less than three conductors converges. The sum of currents converging in the node is zero - the first Rule of Kirchhoff. The first Kirchhoff rule is a consequence of a charge of saving the charge - in the node, the electric charge cannot accumulate.
Slide 23.
The second Rule of Kirchhoff The second rule of Kirchhoff is a consequence of the law of conservation of energy. In any closed circuit of the branched electrical circuit, the algebraic amount II on the resistance of the RI of the respective sections of this circuit is equal to the amount of EDS i applied in it
Slide 24.
The second rule of Kirchhoff
Slide 25.
To compile the equation, you must select the direction of bypass (clockwise or against it). All currents that coincide in the direction of the contour bypass are considered positive. EMF of current sources are considered positive if they create a current directed towards circuit bypass. For example, the Kirchhoff rule for I, II, III k. I I1R1 + I1R1 + I2R2 + i2R2 \u003d - 1 -2 + i-i2R2 - I2R2 + I3R3 + I3R3 \u003d 2 + 3 III1R1 + I1R1 + III1R3 + I3R3 \u003d - 1 + 3 Based on these equations, the chains are calculated.
Slide 26.
7. Contact potential difference. Thermoelectric phenomena electrons with the greatest kinetic energy can fly out of metal into the surrounding space. As a result of the departure of electrons, the "electronic cloud" is formed. There is a dynamic equilibrium between the electronic gas in the metal and the "electronic cloud". The operation of the electron output is the work that needs to be done to remove an electron from metal into airless space. The surface of the metal is a double electrical layer similar to a very thin condenser.
Slide 27.
The potential difference between the capacitor plays depends on the operation of the electron output. Where - electron charge; - the contact difference of potentials between the metal heocrous medium; A - the work of the exit (electron-volt - e-c). The work of the exit depends on the chemical nature of the metal and the state of its surface (pollution, moisture).
Slide 28.
Volta laws: 1. When connecting two conductors made from various metals, a contact difference between the potentials arises between them, which depends only on the chemical composition and temperature. 2. The potential difference between the ends of the chain consisting of sequentially connected metal conductors, which are at the same temperature, does not depend on the chemical composition of intermediate conductors. It is equal to the contact difference of potentials arising from the direct connection of extreme conductors.
Slide 29.
Consider a closed chain consisting of two metal conductors 1 and 2. EMF applied to this chain is equal to the algebraic amount of all potential jumps. If the temperature of the layers are equal, then \u003d 0. If the temperature of the layers are different, for example, wherever is a constant characterizing the properties of the contact of two metals. In this case, thermoelectribution force appears in the closed chain, directly proportional to the difference in the temperatures of both layers.
Slide 30.
Thermoelectric phenomena in metals are widely used to measure temperature. For this, thermal elements or thermocouples are used, which are two wires made from various metals and alloys. The ends of these wires are laid. One spay is placed on Wednesday, the temperature of which is to be measured, and the second is on medium with a constant known temperature. Thermocouples have a number of advantages over conventional thermometers: allow measurement of temperatures over a wide range of tens to thousands of degrees of an absolute scale.
Slide 31.
Gases under normal conditions are dielectricsR \u003d\u003e ∞, they consist of electrically neutral atoms and molecules. In the ionization of gases, electrical current carriers (positive charges) occur. Electric current in gases is called a gas discharge. To carry out a gas discharge to a tube with ionized gas there should be an electric or magnetic field.
Slide 32.
Gas ionization is the decay of a neutral atom on a positive ion and an electron under the action of a ionizer (external influences - strong heating, ultraviolet and X-rays, radioactive radiation, with bombardment of atoms (gas molecules) 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 arising in a single volume of gas over a single period of time. The impact ionization is called the separation from the atom (molecule) of one or more electrons, caused by collision with atoms or electron gas molecules or ions overclocked by the electric field in the discharge.
Slide 34.
Recombination is an electron connection with an ion to a neutral atom. If the action of the ionizer is stopped, the gas becomes a dialectic again. Electron ion
Slide 35.
1. The present gas discharge is a discharge that exists only under the action of external ionizers. The voltamper characteristic of the gas discharge: as U increases, the number of charged particles reaching the electrode increases and the current is increasing to i \u003d Ic, in which all charged particles reach the electrodes. In this case, u \u003d UK saturation current where E is an elementary charge; N0 is the maximum number of pairs of monovalent ions formed in the volume of gas for 1 s.
Slide 36.
2. The mixture of gas discharge is a discharge in a gas that is stored after the termination of the external ionizer. Supported and developed by shock ionization. The inconspicuous gas discharge goes into an independent at the UZ - the ignition voltage. The process of such a transition is called electrical gas supply. Distinguish:
Slide 37.
The crown bit arises at high pressure and in a sharply inhomogeneous field with a large curvature surface, it is used in disinfecting the seeds of crops. Glowing bit arises at low pressures, used in gas drive tubes, gas lasers. Sparkor - when p \u003d RATM IPRI large electric field - lightning (currents up to several thousand amps, length - a few kilometers). Arc discharge - arises 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 a substance characterized by a high degree of ionization of its particles. Plasma is divided into: - weakly ionized ( - the interests of the percent - the 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, magnetodynamic generators.
Slide 39.
Emission phenomena: 1. Photoelectronic emission - pulling under the action of light electrons from the surface of the metals in vacuo. 2. Thermoelectronic emission is the emission of electrons with solid or liquid bodies when they are heated. 3. Secondary electronic emission is a counter stream of electrons from the surface bombarded by electrons in vacuo. Devices based on the phenomenon of thermoelectronic emission are called electronic lamps.
Slide 40.
In solids, the electron interacts not only with its atom, but also with other atoms of the crystal lattice, there is a splitting of energy levels of atoms with the formation of the energy strip. The energy of these electrons can be within the raised areas called the allowed energy zones. Discrete levels are separated by areas of unauthorized energy values \u200b\u200b- forbidden zones (the width of them is commensurate with the width of the forbidden zones). Differences in the electrical properties of various types of solids are explained: 1) the width of the prohibited energy zones; 2) various filling of the electrons of the allowed energy zones
Slide 41.
Many liquids are very poorly conducted by electric current (distilled water, glycerin, kerosene, etc.). Aqueous solutions of salts, acids and alkalis are well conducted by electric current. Electrolysis is the passage of current through the liquid causing the selection on the electrodes of substances included in the electrolyte. Electrolytes are substances with ion conductivity. Ion conductivity is an ordered ion movement under the action of an electric field. Ions are atoms or molecules that have lost one or more electrons who have attached to themselves. Positive ions - cations, negative - anions.
Slide 42.
The electric field is created in the liquid with electrodes ("+" - anode, "-" - cathode). Positive ions (cations) are moving to the cathode, negative - to the anode. The occurrence of ions in electrolytes is due to electrical dissociation - the decay of the molecules of the soluble substance for positive and negative ions as a result of interaction with the solvent (Na + CL-; H + CL-; K + I- ...). The degree of dissociation is indicated by the number of molecules N0, dissociated by ions, to the total number of molecules N0 with heat movement of ions, the reverse ion reunification process, called recombination, occurs.
Slide 43.
Laws M. Faraday (1834). 1. The mass of the substance released on the electrode is directly proportional to the electrical charge Q, which passed through the electrolyte or where k is an electrosal equivalent of a substance; It is equal to the mass of the substance that has been separated by passing through the electrolyte unit of the amount of electricity. Where I is a constant current passing through the electrolyte.
Slide 46.
THANKS FOR ATTENTION
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