General physics. Electric current in metals. Physics presentation on the topic "electric current in metals" What is called a metal

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An electric current in metals is an ordered movement of electrons under the influence of an electric field. Experiments show that when current flows through a metal conductor, there is no transfer of matter, therefore, metal ions do not take part in the transfer of electric charge.

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E. Rikke's experience

In these experiments, an electric current was passed for a year through three well-polished cylinders pressed against each other - copper, aluminum and again copper. The total charge that passed through the cylinders during this time was very large (about 3.5 * 106 C). After completion, it was found that there are only minor traces of mutual penetration of metals, which do not exceed the results of ordinary diffusion of atoms in solids. Measurements carried out with a high degree of accuracy showed that the mass of each of the cylinders remained unchanged. Since the masses of copper and aluminum atoms differ significantly from each other, the mass of the cylinders would have to change noticeably if the charge carriers were ions.

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Experience E. Rikke

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Therefore, free charge carriers in metals are not ions. The huge charge that passed through the cylinders was apparently carried by particles that are the same in both copper and aluminum. As you know, such particles are part of the atoms of all substances - these are electrons. It is natural to assume that it is free electrons that carry out the current in metals.

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The experience of T. Stewart and R. Tolman

A coil with a large number of turns of thin wire was brought into rapid rotation around its axis. The ends of the coil were connected by means of flexible wires to a sensitive ballistic galvanometer. The untwisted coil was sharply decelerated, and a short-term current arose in the circuit, due to the inertia of the charge carriers. The total charge flowing through the circuit was measured by the deflection of the galvanometer needle.

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R. Tolman

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T. Stewart and R. Tolman determined experimentally the specific charge of particles. He was equal

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At the beginning of the 20th century, the German physicist P. Drude and the Dutch physicist H. Lorenz created the classical theory of the electrical conductivity of metals.

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Basic provisions of the theory

The good conductivity of metals is due to the presence of a large number of electrons in them. Under the action of an external electric field, an ordered motion is superimposed on the random motion of electrons, i.e. current occurs.

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3. The strength of the electric current flowing through a metal conductor is:

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4. Since the internal structure of different substances is different, the resistance will also be different. 5. With an increase in the chaotic motion of particles of matter, the body is heated, i.e. heat release. Joule-Lenz law:

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6. For all metals, as the temperature increases, so does the resistance. R=R0(1+at) where a is the temperature coefficient; R0 - specific resistance and resistance of the metal conductor; and R are the resistivity of the conductor and the resistance of the conductor at temperature t.

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Superconductivity

The property of some materials to have strictly zero electrical resistance below a certain temperature. There are many pure elements, alloys and ceramics that pass into the superconducting state.

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In 1911, the Dutch physicist Kamerling-Onnes discovered that when mercury is cooled in liquid helium, its resistance first changes gradually, and then at a temperature of 4.2 K drops sharply to zero. However, zero resistance is not the only hallmark of superconductivity. It is also known from the Drude theory that the conductivity of metals increases with decreasing temperature, that is, the electrical resistance tends to zero.

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H. Kamerling-Onnes

Contents What is electric current? What is electric current? Phenomena that accompany electric current Phenomena that accompany electric current Experience of Tolman and Stewart Experience of Tolman and Stewart Classical electronic theory Classical electronic theory Potential barrier Potential barrier Superconductivity Superconductivity High-temperature superconductivity High-temperature superconductivity

What is electric current? An electric current in metals is an ordered movement of electrons under the influence of an electric field. Experiments show that when current flows through a metal conductor, there is no transfer of matter, therefore, metal ions do not take part in the transfer of electric charge.

Phenomena that accompany electric current 1. the conductor through which the current flows heats up, 2. the electric current can change the chemical composition of the conductor, 3. the current exerts a force on neighboring currents and magnetized bodies 1. the conductor through which the current flows heats up, 2. electric current can change the chemical composition of the conductor, 3. current has a force effect on neighboring currents and magnetized bodies

Experience of Tolman and Stuart (ch1) The scheme of Tolman and Stuart's experiment is shown in the figure. A coil with a large number of turns of thin wire was brought into rapid rotation around its axis. The ends of the coil were connected with flexible wires to a sensitive ballistic galvanometer G. The untwisted coil was sharply decelerated, and a short-term current arose in the circuit due to the inertia of the charge carriers. The total charge flowing through the circuit was measured by the deflection of the galvanometer needle. The scheme of the experiment of Tolman and Stewart is shown in the figure. A coil with a large number of turns of thin wire was brought into rapid rotation around its axis. The ends of the coil were connected with flexible wires to a sensitive ballistic galvanometer G. The untwisted coil was sharply decelerated, and a short-term current arose in the circuit due to the inertia of the charge carriers. The total charge flowing through the circuit was measured by the deflection of the galvanometer needle.

(ch2) When braking a rotating coil, each charge carrier e is affected by a braking force that plays the role of a third-party force, that is, a force of non-electric origin. The third-party force, related to the unit of charge, is by definition the intensity Est of the field of third-party forces: When braking a rotating coil, a braking force acts on each charge carrier e, which plays the role of a third-party force, that is, a force of non-electric origin. External force, related to the unit of charge, by definition is the field strength Est of external forces: external force of external force

(ch3) Therefore, in the circuit, when the coil is braked, an electromotive force arises equal to: Therefore, in the circuit, when the coil is braked, an electromotive force arises equal to: where l is the length of the coil wire. During the braking time of the coil, a charge q will flow through the circuit, equal to: where l is the length of the coil wire. During the braking time of the coil, a charge q will flow through the circuit, equal to:

(h4) Here I is the instantaneous value of the current in the coil, R is the total resistance of the circuit, υ0 is the initial linear speed of the wire. Here I is the instantaneous value of the current in the coil, R is the total resistance of the circuit, υ0 is the initial linear speed of the wire. Hence, the specific charge e / m of free current carriers in metals is: Hence, the specific charge e / m of free current carriers in metals is:

(ch5) All quantities included in the right side of this ratio can be measured. Based on the results of the experiments of Tolman and Stewart, it was found that free charge carriers in metals have a negative sign, and the ratio of the charge of the carrier to its mass is close to the specific charge of the electron obtained from other experiments. So it was found that the carriers of free charges in metals are electrons. All quantities included in the right side of this ratio can be measured. Based on the results of the experiments of Tolman and Stewart, it was found that free charge carriers in metals have a negative sign, and the ratio of the charge of the carrier to its mass is close to the specific charge of the electron obtained from other experiments. So it was found that the carriers of free charges in metals are electrons. According to modern data, the electron charge module (elementary charge) is: According to modern data, the electron charge module (elementary charge) is: and its specific charge is: and its specific charge is:

(ch6) The good electrical conductivity of metals is due to the high concentration of free electrons, equal in order of magnitude to the number of atoms per unit volume. The good electrical conductivity of metals is explained by the high concentration of free electrons, equal in order of magnitude to the number of atoms per unit volume.

Classical electronic theory The assumption that electrons are responsible for the electric current in metals arose much earlier than the experiments of Tolman and Stewart. Back in 1900, the German scientist P. Drude, based on the hypothesis of the existence of free electrons in metals, created an electronic theory of the conductivity of metals. This theory was developed in the works of the Dutch physicist H. Lorenz and is called the classical electron theory. According to this theory, electrons in metals behave like an electron gas, much like an ideal gas. The electron gas fills the space between the ions that form the crystal lattice of the metal The assumption that electrons are responsible for the electric current in metals arose much earlier than the experiments of Tolman and Stewart. Back in 1900, the German scientist P. Drude, based on the hypothesis of the existence of free electrons in metals, created an electronic theory of the conductivity of metals. This theory was developed in the works of the Dutch physicist H. Lorenz and is called the classical electron theory. According to this theory, electrons in metals behave like an electron gas, much like an ideal gas. The electron gas fills the space between the ions that form the crystal lattice of the metal

Potential barrier Due to the interaction with ions, electrons can leave the metal only after overcoming the so-called potential barrier. The height of this barrier is called the work function. At ordinary (room) temperatures, electrons do not have enough energy to overcome the potential barrier. Due to interaction with ions, electrons can leave the metal only after overcoming the so-called potential barrier. The height of this barrier is called the work function. At ordinary (room) temperatures, electrons do not have enough energy to overcome the potential barrier.

Superconductivity According to the classical electronic theory, the resistivity of metals should monotonically decrease upon cooling, remaining finite at all temperatures. Such a dependence is indeed observed experimentally at comparatively high temperatures. At lower temperatures of the order of several kelvins, the resistivity of many metals ceases to depend on temperature and reaches a certain limiting value. However, of greatest interest is the amazing phenomenon of superconductivity, discovered by the Danish physicist H. Kammerling-Onnes in 1911. At some specific temperature Tcr, which is different for different substances, the resistivity abruptly decreases to zero (Fig.). The critical temperature for mercury is 4.1 K, for aluminum 1.2 K, for tin 3.7 K. Superconductivity is observed not only in elements, but also in many chemical compounds and alloys. For example, the compound of niobium with tin (Ni3Sn) has a critical temperature of 18 K. Some substances that pass at low temperatures into a superconducting state are not conductors at ordinary temperatures. At the same time, such "good" conductors as copper and silver do not become superconductors at low temperatures. According to the classical electronic theory, the resistivity of metals should monotonically decrease upon cooling, remaining finite at all temperatures. Such a dependence is indeed observed experimentally at comparatively high temperatures. At lower temperatures of the order of several kelvins, the resistivity of many metals ceases to depend on temperature and reaches a certain limiting value. However, of greatest interest is the amazing phenomenon of superconductivity, discovered by the Danish physicist H. Kammerling-Onnes in 1911. At some specific temperature Tcr, which is different for different substances, the resistivity abruptly decreases to zero (Fig.). The critical temperature for mercury is 4.1 K, for aluminum 1.2 K, for tin 3.7 K. Superconductivity is observed not only in elements, but also in many chemical compounds and alloys. For example, the compound of niobium with tin (Ni3Sn) has a critical temperature of 18 K. Some substances that pass at low temperatures into a superconducting state are not conductors at ordinary temperatures. At the same time, such "good" conductors as copper and silver do not become superconductors at low temperatures.

Substances in the superconducting state have exceptional properties. In practice, the most important of them is the ability for a long time (many years) to maintain without attenuation an electric current excited in a superconducting circuit. Substances in the superconducting state have exceptional properties. In practice, the most important of them is the ability for a long time (many years) to maintain without attenuation an electric current excited in a superconducting circuit. The classical electronic theory is unable to explain the phenomenon of superconductivity. The explanation of the mechanism of this phenomenon was given only 60 years after its discovery on the basis of quantum mechanical concepts. The classical electronic theory is unable to explain the phenomenon of superconductivity. The explanation of the mechanism of this phenomenon was given only 60 years after its discovery on the basis of quantum mechanical concepts. Scientific interest in superconductivity increased as new materials with higher critical temperatures were discovered. A significant step in this direction took place in 1986, when it was discovered that one complex ceramic compound has Tcr = 35 K. Already in the following 1987, physicists managed to create new ceramics with a critical temperature of 98 K, which exceeds the temperature of liquid nitrogen (77 K). Scientific interest in superconductivity increased as new materials with higher critical temperatures were discovered. A significant step in this direction took place in 1986, when it was discovered that one complex ceramic compound has Tcr = 35 K. Already in the following 1987, physicists managed to create new ceramics with a critical temperature of 98 K, which exceeds the temperature of liquid nitrogen (77 K).

High-temperature superconductivity The phenomenon of the transition of substances to the superconducting state at temperatures exceeding the boiling point of liquid nitrogen was called high-temperature superconductivity. In 1988, a ceramic compound based on the elements Tl–Ca–Ba–Cu–O with a critical temperature of 125 K was created. The phenomenon of the transition of substances to the superconducting state at temperatures exceeding the boiling point of liquid nitrogen was called high-temperature superconductivity. In 1988, a ceramic compound based on the elements Tl–Ca–Ba–Cu–O with a critical temperature of 125 K was created. At present, intensive work is underway to search for new substances with even higher values of Tcr. Scientists hope to obtain a substance in a superconducting state at room temperature. If this happens, it will be a real revolution in science, technology and in general in people's lives. Currently, intensive work is underway to search for new substances with even higher values of Tcr. Scientists hope to obtain a substance in a superconducting state at room temperature. If this happens, it will be a real revolution in science, technology and in general in people's lives. It should be noted that the mechanism of high-temperature superconductivity of ceramic materials has not yet been fully elucidated. It should be noted that the mechanism of high-temperature superconductivity of ceramic materials has not yet been fully elucidated.

WHAT IS ELECTRIC CURRENT IN METALS?

Electric current in metals - it is the ordered movement of electrons under the action of an electric field. Experiments show that when current flows through a metal conductor, there is no transfer of matter, therefore, metal ions do not take part in the transfer of electric charge.

NATURE OF ELECTRIC CURRENT IN METALS

Electric current in metal conductors does not cause any changes in these conductors, except for their heating.

The concentration of conduction electrons in a metal is very high: in order of magnitude it is equal to the number of atoms per unit volume of the metal. Electrons in metals are in constant motion. Their random motion resembles the motion of ideal gas molecules. This gave reason to believe that electrons in metals form a kind of electron gas. But the speed of the random movement of electrons in a metal is much greater than the speed of molecules in a gas.

E.RIKKE EXPERIENCE

The German physicist Carl Rikke conducted an experiment in which an electric current passed for a year through three polished cylinders pressed against each other - copper, aluminum and again copper. After completion, it was found that there are only minor traces of mutual penetration of metals, which do not exceed the results of ordinary diffusion of atoms in solids. Measurements carried out with a high degree of accuracy showed that the mass of each of the cylinders remained unchanged. Since the masses of copper and aluminum atoms differ significantly from each other, the mass of the cylinders would have to change noticeably if the charge carriers were ions. Therefore, free charge carriers in metals are not ions. The huge charge that passed through the cylinders was apparently carried by particles that are the same in both copper and aluminum. It is natural to assume that it is free electrons that carry out the current in metals.

Carl Victor Eduard Rikke

EXPERIENCE L.I. MANDELSHTAMA and N.D. PAPALEKSI

Russian scientists L. I. Mandelstam and N. D. Papaleksi in 1913 staged an original experiment. The coil with the wire began to twist in different directions. Unwind, clockwise, then abruptly stop and - back. They reasoned something like this: if electrons really have mass, then when the coil suddenly stops, the electrons should continue to move by inertia for some time. And so it happened. We connected a telephone to the ends of the wire and heard a sound, which meant that current was flowing through it.

Mandelstam Leonid Isaakovich

Nikolai Dmitrievich Papalexy (1880-1947)

THE EXPERIENCE OF T. STUART AND R. TOLMAN

The experience of Mandelstam and Papaleksi was repeated in 1916 by the American scientists Tolman and Stuart.

A coil with a large number of turns of thin wire was brought into rapid rotation around its axis. The ends of the coil were connected with flexible wires to a sensitive ballistic galvanometer. The untwisted coil was sharply decelerated, a short-term current arose in the circuit due to the inertia of the charge carriers. The total charge flowing through the circuit was measured by the deflection of the galvanometer needle.

Butler Stuart Thomas

Richard Chase Tolman

CLASSICAL ELECTRONIC THEORY

The assumption that electrons are responsible for the electric current in metals existed even before the experiment of Stewart and Tolman. In 1900, the German scientist P. Drude, based on the hypothesis of the existence of free electrons in metals, created his electronic theory of the conductivity of metals, named after classical electronic theory . According to this theory, electrons in metals behave like an electron gas, much like an ideal gas. It fills the space between the ions that form the crystal lattice of the metal

The figure shows the trajectory of one of the free electrons in the crystal lattice of a metal

MAIN PROVISIONS OF THE THEORY:

The presence of a large number of electrons in metals contributes to their good conductivity.
Under the action of an external electric field, an ordered motion is superimposed on the random motion of electrons, i.e. current occurs.
The strength of the electric current flowing through a metal conductor is:
Since the internal structure of different substances is different, the resistance will also be different.
With an increase in the chaotic motion of particles of a substance, the body is heated, i.e. heat release. Here the Joule-Lenz law is observed:

l \u003d e * n * S * Ū d

SUPERCONDUCTIVITY OF METALS AND ALLOYS

Some metals and alloys have superconductivity, the property of having strictly zero electrical resistance when they reach a temperature below a certain value (critical temperature).

The phenomenon of superconductivity was discovered by the Dutch physicist H. Kamerling - Ohness in 1911 in mercury (T cr = 4.2 o K).

ELECTRIC CURRENT APPLICATION:

receiving strong magnetic fields
transmission of electricity from source to consumer
powerful electromagnets with superconducting winding in generators, electric motors and accelerators, in heating devices

Currently, there is a big problem in the energy sector associated with large losses during the transmission of electricity through wires.

Possible solution to the problem:

Construction of additional transmission lines - replacement of wires with large cross-sections - voltage increase - phase splitting

Class: 11

Presentation for the lesson

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Lesson Objectives:

To reveal the concept of the physical nature of the electric current in metals, experimental confirmation of the electronic theory;

Continue the formation of natural scientific ideas on the topic under study

Create conditions for the formation of cognitive interest, student activity

Formation of skills;

Formation of communicative communication.

Equipment: interactive complex SMART Board Notebook, local area network of computers, Internet.

Lesson teaching method: combined.

Epigraph of the lesson:

Strive to comprehend science ever deeper,
Longing for the knowledge of the eternal.
Only the first knowledge will shine on you light,
You will know: there is no limit to knowledge.

Ferdowsi
(Persian and Tajik poet, 940-1030)

Lesson plan.

I. Organizing moment

II. Group work

III. Discussion of the results, installation of the presentation

IV. Reflection

V. Homework

During the classes

Hello guys! Sit down. Today we will work in groups.

Tasks for groups:

I. Physical nature of charges in metals.

II. K. Rikke's experience.

III. Experience of Stuart, Tolman. Experience of Mandelstam, Papaleksi.

IV. Drude theory.

V. Volt-ampere characteristic of metals. Ohm's law.

VI. The dependence of the resistance of conductors on temperature.

VII. Superconductivity.

1. Electrical conductivity is the ability of substances to conduct an electric current under the influence of an external electric field.

According to the physical nature of charges - carriers of electric current, electrical conductivity is divided into:

A) electronic

B) ionic

B) mixed.

2. For each substance under given conditions, a certain dependence of the current strength on the potential difference is characteristic.

According to the resistivity of a substance, it is customary to divide it into:

A) conductors (p< 10 -2 Ом*м)

B) dielectrics (p\u003e 10 -8 Ohm * m)

C) semiconductors (10 -2 Ohm * m> p> 10 -8 Ohm * m)

However, such a division is conditional, because under the influence of a number of factors (heating, irradiation, impurities), the resistivity of substances and their volt-ampere characteristics change, and sometimes very significantly.

3. Carriers of free charges in metals are electrons. Proven by classical experiments K. Rikke (1901) - German physicist; L.I. Mandelstam and N. D. Papaleksi (1913) - our compatriots; T. Stewart and R. Tolman (1916) - American physicists.

K. Rikke's experience

Rikke folded three pre-weighted cylinders (two copper and one aluminum) with polished ends so that the aluminum one was between the copper ones. Then the cylinders were connected to a DC circuit: a large current passed through them during the year. During that time, an electric charge equal to approximately 3.5 million C passed through the electric cylinders. The secondary interaction of the cylinders, carried out with up to 0.03 mg, showed that the mass of the cylinders did not change as a result of the experiment. When examining the contacting ends under a microscope, it was found that there are only minor traces of penetration of metals, which do not exceed the results of ordinary diffusion of atoms in solids. The results of the experiment indicated that ions do not participate in charge transfer in metals.

L.I. Mandelstam

N. . Papalexy

Experience of L. I. Mandelstam and N. D. Papaleksi

Russian scientists L. I. Mandelstam (1879-1949; founder of the school of radio physicists) and N. D. Papaleksi (1880-1947; the largest Soviet physicist, academician, chairman of the All-Union Scientific Council for Radio Physics and Radio Engineering under the Academy of Sciences of the USSR) in 1913 delivered the original an experience. They took a coil of wire and began to twist it in different directions.

Unwind, for example, clockwise, then abruptly stop and - back.

They reasoned something like this: if electrons really have mass, then when the coil suddenly stops, the electrons should continue to move by inertia for some time. The movement of electrons through a wire is an electric current. As planned, so it happened. We connected a telephone to the ends of the wire and heard a sound. Once a sound is heard in the phone, therefore, current flows through it.

T. Stewart

The experience of T. Stewart and R. Tolman

Let's take a coil that can rotate around its axis. The ends of the coil are connected to the galvanometer by means of sliding contacts. If the coil, which is in rapid rotation, is braked sharply, then the free electrons in the wire will continue to move by inertia, as a result of which the galvanometer must register a current pulse.

Drude theory

Electrons in a metal are considered as an electron gas, to which the kinetic theory of gases can be applied. It is believed that electrons, like gas atoms in kinetic theory, are identical solid spheres that move in straight lines until they collide with each other. It is assumed that the duration of a single collision is negligible, and that no other forces act between the molecules, except those arising at the moment of the collision. Since an electron is a negatively charged particle, then in order to comply with the condition of electrical neutrality in a solid, there must also be particles of a different kind - positively charged. Drude suggested that the compensating positive charge belongs to much heavier particles (ions), which he considered immobile. At the time of Drude, it was not clear why there are free electrons and positively charged ions in the metal, and what these ions are. Only the quantum theory of solids could give answers to these questions. For many substances, however, one can simply assume that the electron gas consists of external valence electrons weakly bound to the nucleus, which are “liberated” in the metal and are able to move freely through the metal, while atomic nuclei with electrons of inner shells (atomic cores) remain unchanged. and play the role of fixed positive ions of the Drude theory.

Electric current in metals

All metals are conductors of electric current and consist of a spatial crystal lattice, the nodes of which coincide with the centers of positive ions, and free electrons move randomly around the ions.

Fundamentals of the electronic theory of conductivity of metals.

A metal can be described by the following model: the crystal lattice of ions is immersed in an ideal electron gas consisting of free electrons. In most metals, each atom is ionized, so the concentration of free electrons is approximately equal to the concentration of atoms 10 23 - 10 29 m -3 and almost does not depend on temperature.
Free electrons in metals are in continuous chaotic motion.
An electric current in a metal is formed only due to the ordered movement of free electrons.
Colliding with ions vibrating at the nodes of the crystal lattice, electrons give them excess energy. This is why conductors heat up when current flows.

Electric current in metals.

Superconductivity

The phenomenon of reducing resistivity to zero at a temperature other than absolute zero is called superconductivity. Materials that exhibit the ability to pass at certain temperatures other than absolute zero into a superconducting state are called superconductors.

The passage of current in a superconductor occurs without energy loss, therefore, once excited in a superconducting ring, an electric current can exist indefinitely without change.

Superconducting materials are already being used in electromagnets. Research is underway to create superconducting power lines.

The application of the phenomenon of superconductivity in wide practice may become a reality in the coming years due to the discovery in 1986 of the superconductivity of ceramics - compounds of lanthanum, barium, copper and oxygen. The superconductivity of such ceramics is retained up to temperatures of about 100 K.

Well done boys! They did an excellent job. It turned out to be a good presentation. Thank you for the lesson!

Literature.

Gorbushin Sh.A. Reference notes for the study of physics for the course of the secondary school. - Izhevsk "Udmurtia", 1992.
Lanina I.Ya. Formation of cognitive interests of students in physics lessons: A book for teachers. – M.: Enlightenment, 1985.
Physics lesson in modern school. Creative search for teachers: A book for teachers / Comp. E.M. Braverman / Edited by V.G. Razumovsky.- M.: Enlightenment, 1993
Digelev F.M. From the history of physics and the life of its creators: A book for students. - M .: Education, 1986.
Kartsev V.L. Adventures of great equations. - 3rd edition - M .: Knowledge, 1986. (Life of wonderful ideas).

Electric current in metals Savvateeva Svetlana Nikolaevna, teacher of physics, MBOU "Kemetskaya secondary school" of the Bologovsky district of the Tver region. TODAY IN THE LESSON The secret becomes clear. What is hidden behind the concept "Current carriers in metals"? What are the difficulties of the classical theory of electrical conductivity of metals? Why do incandescent bulbs burn out? Why do they burn out when turned on? How to lose resistance? REPEAT

What is electric current?
What are the conditions for the existence of a current?
What actions of the current do you know?
What is the direction of current?
What is the value of current in an electrical circuit?
What is the unit of current?
On what quantities does the current strength depend?
What is the speed of current propagation in the conductor?
What is the speed of the ordered movement of electrons?
Does resistance depend on current and voltage?
How is Ohm's law formulated for a section of a chain and for a complete chain?

ELECTRICAL CONDUCTIVITY OF VARIOUS SUBSTANCES

Mandelstam and Papaleksi (1913)

Stewart and Tolman (1916)

In the direction of current -< 0

By І J I - q ⁄ m = e ⁄ m ) these are electrons!

Rikke's experience (German) - 1901 Year! M = const, these are not ions!

NATURE OF CHARGE CARRIERS IN METALS

Electric current in metals is the directed movement of electrons.

Theory of electrical conductivity of metals

P. Druse, 1900:

free electrons - "electronic gas";
electrons move according to Newton's laws;
free electrons collide with crystal ions. gratings;
upon collision, electrons transfer their kinetic energy to ions;
the average speed is proportional to the intensity and, therefore, the potential difference;

R= f (ρ, l, s, t)

resistance thermometers

Benefits: Helps to measure very low and very high temperatures.

superconductivity Mercury in liquid helium

The explanation is based on quantum theory.

D. Bardeen, L. Cooper, D. Schrieffer (Amer.) and

N. Bogolyubov (co-student in 1957)

Application of superconductivity!

obtaining high currents, magnetic fields;
transmission of electricity without loss.

control test

How do free electrons move in metals?
How do free electrons move in metals under the action of an electric field?
.What particles are located at the nodes of the crystal lattice of metals and what charge do they have?
What effect of electric current is used in electric lamps?
The movement of which particles is taken as the direction of the current in the conductor?
Why do metals get hot when current is passed through them?
How does the resistance of metals change when they are cooled?

1. B. 2. D. 3.B. 4.G. 5.B. 6.B. 7.B.

SOLVE THE PROBLEM

1. The electrical resistance of the tungsten filament of an electric lamp at a temperature of 23 ° C is 4 ohms.

Find the electrical resistance of the filament at 0°C.

(Answer: 3.6 ohms)

2. The electrical resistance of a tungsten filament at 0°C is 3.6 ohms. Find electrical resistance

At a temperature of 2700 K.

(Answer: 45.5 ohms)

3. The electrical resistance of the wire at 20°C is 25 ohms, at 60°C it is 20 ohms. Find

Temperature coefficient of electrical resistance.