Actions of electric current: thermal, chemical, magnetic, light and mechanical. Electric current in metals. Electric current action. Direction of current

Theme. Electric current in metals

Lesson objectives: to form a concept of the nature of electric current in metals and its direction; find out what actions an electric current is capable of performing; show the practical orientation of the studied material; to form a scientific materialistic worldview, develop logical thinking, form an idea of \u200b\u200bthe process of scientific cognition; develop the ability to listen and be heard, instill a culture of mental work, foster feelings of pride and respect for people who have contributed to the development of science

Lesson type: lesson in assimilation of new knowledge

During the classes

Organizational moment in the form of a slide show under the poem by V. Shefner

I'm not tired of being surprised yet

The miracles that are on earth -

And the computer on the table.

Airplanes fly through the clouds

Ships walk on the sea, -

How before these mighty things

Could people dream?

How could they come up with this,

That the cassette sings a song to us

That you will press the button with your hand -

And in the middle of the night, the day comes.

I commit myself to the tram

I look at the movie screen.

Understanding this technique,

I am amazed all the same.

Current flows through the wire

The satellite walks through the heavens ...

A man should be amazed

Human miracles.

Updating basic knowledge

What is Electric Current?

List the conditions for the existence of an electric current.

What substances are called conductors of electricity?

What is a current source? What is its purpose?

Presentation of new material

All metals are conductors of electric current and in the solid state have a crystalline structure.

You know from the chemistry course that valence electrons in metals easily leave their atom and become free. Positive ions are located in the nodes of the crystal lattice of metals, and electrons move in the space between them. Electrons are not bound to the nuclei of their atoms and move randomly, which is why they are called free.In turn, free electrons in metals are called electronic gas.

In metals, electronic conductivity

The absolute value of the negative charge of all free electrons is equal to the positive charge of all ions in the lattice. Therefore, under normal conditions, the metal is electrically neutral.

If an electric field is created in metals, then free electrons will continue to move chaotically and will shift towards the positive pole of the current source. Then the movement of electrons becomes directional and an electric current arises.

Electric current in metals is the ordered movement of free electrons

The experience of the Russian scientists Mandelstam and Papaleksi, carried out by them in 1913, experimentally showed that the conductivity of metals is due to the movement of free electrons.

L.I. Mandelstam (1879-1949; founder of the school of radiophysicists) and N.D. Papaleksi (1880-1947; a prominent Soviet physicist, academician, chairman of the All-Union Scientific Council on Radiophysics and Radio Engineering at the Academy of Sciences of the USSR) establishing the nature of the current in metals.

They took a coil of wire and began to twist it in different directions. Spin, for example, clockwise, then abruptly stop and - back.

They reasoned something like this: if a metal conductor is set in rapid motion and then suddenly stopped, then when the coil suddenly stops, the electrons must move by inertia for some time. As a result, a short-term current will appear in the conductor, which can be fixed with a galvanometer. By the deviation of the arrow of the device, it is possible to establish the sign of the charge of moving particles, and from the ratio of the charge of particles to their mass, it is possible to establish which particles create the current.

The movement of electrons through a wire is an electric current. As conceived, 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.

The experience of Mandelstam and Papaleksi in 1916 was repeated by the American scientists Tolman and Stewart. They also twisted the coil, but instead of a telephone, they connected a device to measure the charge. They managed to measure the mass of the particle. Tolman and Stewart's data were later checked and refined many times by other scientists, and now you know that the mass of an electron

m e \u003d 9, 1 ∙ 10 -31 kg

The specific charge of an electron, that is, the charge per unit mass,

The speed of movement of the electrons themselves in a conductor under the action of an electric field is small (several mm per second).

But why does the light turn on almost instantly when the electrical circuit is closed?

It turns out that the electric field propagates at a tremendous speed (close to c \u003d 300,000 km / s) along the entire length of the conductor. Under the action of an electric field, free electrons come into ordered motion, which are not only in the supply conductors, but also in the spiral of the lamp itself.

Therefore, when they talk about the speed of propagation of an electric current in a conductor, they mean the speed of propagation of an electric field along the conductor.

The main characteristics of the current in metals (conductors):

a) current strength in the conductor

I \u003d envS where e \u003d 1.6 ∙ 10 -19 C - module

electron charge

n is the concentration of electrons

v ≈ 10 4 - c medium speed

electrons

S - area of \u200b\u200bthe transverse

conductor cross-section

b) current-voltage characteristic (dependence of the current strength in

conductor from voltage)

I \u003d

c) the dependence of the resistance of the conductor on temperature

In the experiment that we talked about today, after the conductor stops, the directional movement of the particles quickly stops, because the conductor resists the current. The resistance of a metal conductor depends not only on its geometric dimensions and substance, but also on temperature. This can be confirmed by such experience. If you connect a steel coil with a current source and gradually heat it, then at a constant voltage, the current will decrease. This indicates that the resistance of the spiral is increasing.

R \u003d R 0 (1 + t) where R 0 - resistance up to

heating

- temperature change

α -temperature coefficient

resistance

If you carry out the same experiment with other spirals, you will notice that with an increase in temperature, the resistance of these spirals also increases, but its change will be different.

Knowing how the resistance of a metal conductor depends on temperature, by measuring the resistance, you can determine the temperature of the conductor. This fact underlies the work of the so-called resistance thermometers.

Question to students:

Where is electric current applied in metals ? (Conductors for transmitting electricity over a distance, a transformer core for converting electrical energy, pipes to prevent corrosion, a lamp spiral for lighting, a heating element spiral for heating, etc.)

Working with the tutorial (p. 103 item 3)

What is the phenomenon of superconductivity?

Lesson summary

What is the nature of the motion of electrons in metals in the absence of an electric field?

And in the presence of an electric field?

What is electric current in metals?

How was the nature of electric current in metals proven?

What does the resistance of metals depend on?

Abstract on the topic:
"Electric current in metals"

Introduction

Electric current is present everywhere, it flows: in our body, transmitting nerve impulses, in the atmosphere, causing lightning strikes and the like, and, of course, in electrical appliances, flowing through metal wires.
Electric current in metals is the movement of negatively charged free electrons under the action of an electric field in the space between the positively charged ions of the ordered crystal lattice of the metal. Experiments show that when a current flows through a metal conductor, the transfer of matter does not occur, therefore, metal ions do not take part in the transfer of an electric charge.
In other words, metals have electrons that can travel through the metal. They are called conduction electrons. Positive charges in a metal are ions that form a crystal lattice. In the absence of an external field, electrons in a metal move chaotically, undergoing collisions with lattice ions. Under the influence of an external electric field, electrons begin to move in order, superimposed on their previous chaotic fluctuations. In the process of ordered motion, the electrons still collide with the ions of the crystal lattice. This is what causes electrical resistance.

The nature of electric current in metals.

All metals in solid and liquid state are conductors of electric current. Special experiments have shown that when an electric current passes, the mass of metal conductors remains constant, and their chemical composition does not change either. On this basis, it could be assumed that only electrons participate in the creation of an electric current in metals. The assumption about the electronic nature of electric current in metals was confirmed by the experiments of Soviet physicists L. I. Mandel'shtam and N. D. Papaleksi and American physicists T. Stewart and R. Tolman. In these experiments, it was found that when a rapidly rotating coil stops abruptly, an electric current arises in the coil wire, created by negatively charged particles - electrons.
In the absence of an electric field, free electrons move randomly in the metal crystal. Under the action of an electric field, free electrons, in addition to chaotic motion, acquire an ordered motion in one direction, and an electric current arises in the conductor. Free electrons collide with the ions of the crystal lattice, giving them at each collision the kinetic energy acquired during free path under the action of an electric field. As a result, the ordered motion of electrons in a metal can be regarded as uniform motion with a certain constant speed.
Since the kinetic energy of electrons, acquired under the action of an electric field, is transferred by collision of ions of the crystal lattice, then when a direct current passes, the conductor heats up.

Laws in a metallic environment. Current in a metal conductor. Conduction current density. Conductor resistivity.

The current in a metal conductor is determined by the formula:

Where I is the current in the conductor, e is the modulus of the electron charge, n 0 is the concentration of conduction electrons, is the average speed of the ordered motion of electrons, S is the cross-sectional area of \u200b\u200bthe conductor.

The conduction current density is numerically equal to the charge passing through 1 s through a unit of surface area perpendicular to the direction of the current.

Where j is the current density.

For most metals, virtually every atom is ionized. And since the concentration of conduction electrons of a monovalent metal is

Where N a is Avogadro's constant, A is the atomic mass of the metal,? - the density of the metal, then we get that the concentration is determined in the range of 10 28 - 10 29 m -3.

Ohm's law for a homogeneous section of a chain:

Where U is the voltage in the section, R is the resistance of the section.

For a homogeneous section of the chain:

Where? Y is the resistivity of the conductor, l is the length of the conductor, S is the cross-sectional area of \u200b\u200bthe conductor.

The resistivity of the conductor depends on temperature, and this dependence is expressed by the ratio:

Y \u003d? oh (1 +?? t)

Where? oy - resistivity of a metal conductor at a temperature of T \u003d 273K,? - thermal resistance coefficient,? Т \u003d Т - Т о - temperature change.

Volt - ampere characteristic of metals

The strength of the current in conductors, according to Ohm's law, is directly proportional to the voltage. This dependence takes place for conductors with a strictly specified resistance (for resistors).

The tangent of the slope of the graph is equal to the conductance of the conductor. Conductivity is the reciprocal of the resistance

Where G is conductivity.

But since the resistance of metals depends on temperature, the volt-ampere characteristic of metals is not linear.

Mechanism of conduction

The carriers of current in metals are free electrons, that is, electrons weakly bound to the ions of the crystal lattice of the metal. This idea of \u200b\u200bthe nature of current carriers in metals is based on the electronic theory of metal conductivity, created by the German physicist P. Drude (1863-1906) and later developed by the Dutch physicist H. Lorentz, as well as on a number of classical experiments confirming the provisions of the electronic theory.
The electrons of the outer shells of atoms (valence electrons) are socialized, that is, they simultaneously belong to many atoms. These electrons can move randomly, forming an "electron gas", in which positive ions located at the sites of the crystal lattice are immersed. The role of the electron gas in metals is very important. Chaotically moving electrons make a strong metallic bond, holding together a lattice built of identically charged (and, therefore, mutually repulsive) ions. If we imagine that absolutely all free electrons were removed from the metal, then the ions having the same charge sign would scatter to the sides, and the lattice would “explode”.
It is the free electrons participating in the transfer of electric charge, creating an electric current, and causing the high electrical and thermal conductivity of metal crystals.

Application of current in metals

Receiving strong magnetic fields;

Powerful electromagnets with superconducting windings in accelerators and generators;

Used to transmit electricity over a distance

In heating devices

Superconductivity phenomenon

However, the most interesting is the amazing phenomenon of superconductivity, discovered by the Danish physicist H. Kammerling-Onnes in 1911. At some definite temperature Tcr, which is different for different substances, the resistivity abruptly decreases to zero (Fig. 1).
The critical temperature is 4.1 K for mercury, 1.2 K for aluminum, and 3.7 K for tin. 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 go superconducting at low temperatures are not conductors at ordinary temperatures. At the same time, such “good” conductors like copper and silver do not become superconductors at low temperatures.

Substances in a superconducting state have exceptional properties. In practice, the most important of them is the ability for a long time (many years) to maintain without damping the electric current excited in the 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.

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 had Tcr \u003d 35 K. Already in the next 1987, physicists managed to create a new ceramic with a critical temperature of 98 K, exceeding the temperature of liquid nitrogen (77 K). The phenomenon of the transition of substances to a superconducting state at temperatures exceeding the boiling point of liquid nitrogen was called high-temperature superconductivity.
In 1988, a ceramic compound based on the Tl – Ca – Ba – Cu – O elements with a critical temperature of 125 K was created. At present, intensive work is underway to search for new substances with even higher Tcr values. Scientists hope to get 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 the life of people. It should be noted that the mechanism of high-temperature superconductivity of ceramic materials has not yet been fully elucidated.

Rikke's experience

The ordered movement of ions would mean a gradual transfer of matter along the direction of the electric current. Therefore, you just need to pass current through the conductor for a very long time and see what happens in the end. This kind of experiment was carried out by E. Ricke in 1901.
The electrical circuit included three cylinders pressed against each other: two copper at the edges and one aluminum between them (Fig. 2). An electric current was passed through this circuit for a year.

Picture 2
For a year, a charge of more than three million pendants passed through the cylinders. Suppose that each metal atom loses one valence electron, so that the charge of the ion is equal to the elementary charge e \u003d Cl. If the current is created by the movement of positive ions, then it is easy to calculate that such a value of the charge passed along the circuit corresponds to the transfer along the circuit of about 2 kg of copper.
However, after the separation of the cylinders, only a slight penetration of metals into each other was found, due to the natural diffusion of their atoms (and nothing more). Electric current in metals is not accompanied by the transfer of matter; therefore, positive metal ions do not take part in creating current.

Stewart's Experience - Tolman

Direct experimental proof that electric current in metals is created by the movement of free electrons was given in the experiment of T. Stewart and R. Tolman (1916).
The Stuart-Tolman experiment was preceded by qualitative observations made four years earlier by Russian physicists L. I. Mandel'shtam and N. D. Papaleksi. They drew attention to the so-called electro-inertial effect: if you sharply slow down a moving conductor, then a short-term current pulse arises in it. The effect is explained by the fact that for a short time after braking the conductor, its free charges continue to move by inertia.
However, Mandelstam and Papaleksi did not receive any quantitative results, and their observations were not published. The honor to call the experiment by its own name belongs to Stewart and Tolman, who not only observed the indicated electrical inertial effect, but also made the necessary measurements and calculations.

Figure 3

The Stewart and Tolman setup is shown in Fig. 3.
A coil with a large number of turns of a metal wire was brought into rapid rotation around its axis. The ends of the winding with the help of sliding contacts were connected to a special device - a ballistic galvanometer, which allows you to measure the charge passing through it.
After a sharp deceleration of the coil, a current pulse appeared in the circuit. The direction of the current indicated that it was caused by the movement of negative charges. Measuring the total charge passing through the circuit with a ballistic galvanometer, Stewart and Tolman calculated the ratio q / m of the charge of one particle to its mass. It turned out to be equal to the ratio e / m for an electron, which at that time was already well known.
So it was finally found out that the carriers of free charges in metals are free electrons. As you can see, this fact, which is well known to you for a long time, was established relatively late - given that metal conductors by that time had been actively used for more than a century in a wide variety of experiments on electromagnetism.

Conclusion

Electric current in a metal is the ordered movement of electrons.
When metals interact with an electromagnetic field, their high electrical conductivity plays the main role; therefore, an important aspect of the analysis of this interaction is to clarify the physical nature of the response of a conducting medium to the presence of an electric current in it, which manifests itself nontrivially due to its nonthermal action.
In the classical electronic theory of metals, it is assumed that the motion of electrons obeys the laws of classical mechanics. The interaction of electrons with each other is neglected, the interaction of electrons with ions is reduced only to collisions. We can say that conduction electrons are considered as an electron gas, similar to the ideal atomic gas in molecular physics.

List of references

etc.................

Definition 1

Electric shock in metals called the ordered motion of electrons under the action of an electric field.

Based on the experiments, it is clear that a metal conductor does not transfer matter, that is, metal ions do not participate in the movement of an electric charge.

During the research, evidence was obtained of the electronic nature of the current in metals. Back in 1913 L.I. Mandelstam and N.D. Papaleksi produced first quality results. And in 1916, R. Tolman and B. Stewart modernized the existing technique and carried out quantitative measurements, which proved that the movement of electrons occurs under the action of current in metal conductors.

Picture 1 . 12 . 1 shows a diagram of Tolman and Stewart. The coil, consisting of a large number of turns of thin wire, was driven by rotation around its axis. Its ends were attached to a ballistic galvanometer G. The coil was abruptly decelerated, which was a consequence of the occurrence of a short-term current due to the inertia of the charge carrier. The total charge was measured by moving the arrows of the galvanometer.

Picture 1 . 12 . 1 . Tolman and Stewart's experiment diagram.

During braking of the rotating coil, the force F \u003d - m d υ d t, called decelerating, acted on each charge carrier e. F played the role of an external force, in other words, of non-electrical origin. It is this force, characterized by a unit of charge, that is the field strength of external forces E with m:

E with т \u003d - m e d υ d t.

That is, when the coil is braking, an electromotive force δ occurs, equal to δ \u003d E with t l \u003d m e d υ d t l, where l is the length of the coil wire. A certain time interval of the coil braking process is due to the flow of the charge q through the circuit:

q \u003d ∫ I d t \u003d 1 R ∫ δ d t \u003d m e l υ 0 R.

This formula explains that l is the instantaneous value of the current in the coil, R is the total resistance of the circuit, υ 0 is the initial linear speed of the wire. It can be seen that the determination of the specific charge e m in metals is made based on the formula:

e m \u003d l υ 0 R q.

The values \u200b\u200bon the right side can be measured. Based on the results of the experiments of Tolman and Stewart, it was established that the carriers of free charge have a negative sign, and the ratio of the carrier in its mass is close to the value of the specific charge of an electron obtained in other experiments. It was revealed that electrons are carriers of free charges.

Modern data show that the modulus of the electron charge, that is, the elementary charge, is equal to e \u003d 1.60 218 10 - 19 K l, and the designation of its specific charge is e m \u003d 1.75882 10 11 K l / k g.

In the presence of an excellent concentration of free electrons, it makes sense to talk about good electrical conductivity of metals. This was revealed even before the experiments of Tolman and Stewart. In 1900, P. Drude, based on the hypothesis of the existence of free electrons in metals, created the electronic theory of the conductivity of metals. It was developed and expanded by H. Lorentz, after which it was named the classical electronic theory. On its basis, it was understood that electrons behave like an electron gas, similar to an ideal one in its state. Picture 1 . 12 . 2 shows how it can fill the space between the ions that have already formed the crystal lattice of the metal.

Picture 1 . 12 . 2. Gas of free electrons in the crystal lattice of the metal. The trajectory of one of the electrons is shown.

Definition 2

After the interaction of electrons with ions, the first leave the metal, overcoming only the potential barrier.

The height of such a barrier is called exit work.

Room temperature prevents electrons from passing through this barrier. The potential energy of the exit of an electron after interaction with the crystal lattice is much less than when an electron is removed from the conductor.

Definition 3

Location e in a conductor is characterized by the presence of a potential well, the depth of which is called potential barrier.

The lattice ions and electrons take part in thermal motion. Due to the thermal vibrations of ions near the equilibrium positions and the chaotic motion of free electrons, when the former collide with the latter, the thermodynamic equilibrium between the electrons and the lattice is enhanced.

Theorem 1

According to the Drude-Lorentz theory, we have that electrons have the same average energy of thermal motion as molecules of a monatomic ideal gas. This makes it possible to estimate the average velocity υ т ¯ of the thermal motion of electrons using the molecular kinetic theory.

Room temperature gives a value of 10 5 m / s.

If you impose an external electric field in a metal conductor, then there will be a thermally ordered motion of electrons (electric current), that is, drift. Determination of its average speed υ d ¯ is carried out according to the interval of available time ∆ t through the cross-section S of the conductor of electrons that are in the volume S υ d ∆ t.

The number of such e is equal to n S υ d ∆ t, where n takes the value of the average concentration of free electrons, which is equal to the number of atoms per unit volume of the metal conductor. For the available amount of time ∆ t, a charge ∆ q \u003d e n S υ d ∆ t passes through the conductor section.

Then I \u003d ∆ q ∆ t \u003d e n S υ d or υ d \u003d I e n S.

The concentration of n atoms in metals is in the range of 10 28 - 10 29 m - 3.

The formula makes it possible to estimate the average speed υ d ¯ of the ordered motion of electrons with a value in the interval of 0.6 - 6 m m / s for a conductor with a cross section of 1 m m 2 and a passing current of 10 A.

Definition 4

average speed υ d ¯ of the ordered motion of electrons in metal conductors is many orders of magnitude less than the speed υ t of their thermal motion υ d ≪ υ t.

Picture 1 . 12 . 3 demonstrates the nature of the motion of a free e in the crystal lattice.

Picture 1 . 12 . 3. The movement of a free electron in the crystal lattice: a - chaotic movement of an electron in the crystal lattice of the metal; b - chaotic motion with a drift due to the electric field. The scale of the drift υ d ¯ ∆ t is greatly exaggerated.

The presence of a low drift rate does not correspond to experience when the current of the entire DC circuit is established instantly. The closure is performed using the action of an electric field with a speed of c \u003d 3 · 10 8 m / s. After a lapse of time l c (l is the length of the chain) a stationary distribution of the electric field is established along the chain. An ordered movement of electrons takes place in it.

The classical electronic theory of metals assumes that their motion is subject to the laws of Newtonian mechanics. This theory is characterized by the fact that the interaction of electrons with each other is neglected, and the interaction with positive ions is regarded as collisions, at each of which e imparts the accumulated energy to the lattice. Therefore, it is generally accepted that after the collision the motion of the electron is characterized by zero drift velocity.

Absolutely all of the above suggested assumptions are approximate. This makes it possible to explain the laws of electric current in metal conductors, based on the electronic classical theory.

Ohm's law

Definition 5

In the interval between collisions, a force equal to e E in modulus acts on the electron, resulting in an acceleration e m E.

The end of the free path is characterized by the electron drift velocity, which is determined by the formula

υ d \u003d υ d m a x \u003d e E m τ.

The free run time is denoted by τ. It simplifies calculations for finding the value of all electrons. The average drift speed υ d is equal to half the maximum value:

υ d \u003d 1 2 υ d m a x \u003d 1 2 e E m τ.

If there is a conductor with a length l, a cross-section S with an electron concentration n, then the record of finding the current in the conductor is:

I \u003d e n S υ d \u003d 1 2 e 2 τ n S m E \u003d e 2 τ n S 2 m l U.

U \u003d E l is the voltage at the ends of the conductor. The formula expresses Ohm's law for a metal conductor. Then the electrical resistance must be found:

R \u003d 2 m e 2 n τ l S.

Resistivity ρ and conductivity ν are expressed as:

ρ \u003d 2 m e 2 n τ; ν \u003d 1 ρ \u003d e 2 n τ 2 m.

Joule-Lenz law

The end of the path of electrons under the action of the field is characterized by kinetic energy

1 2 m (υ d) m a x 2 \u003d 1 2 e 2 τ 2 m E 2.

Definition 6

Based on the assumptions, the energy is transferred to the lattice during collisions, and subsequently turns into heat.

The time ∆ t of each electron is tested ∆ t τ collisions. A conductor with cross section S and length l has n S l electrons. Then the released heat in the conductor for ∆ t is equal to

∆ Q \u003d n S l ∆ t τ e 2 τ 2 2 m E 2 \u003d n e 2 τ 2 m S l U 2 ∆ t \u003d U 2 R ∆ t.

This ratio expresses joule-Lenz law.

Thanks to the classical theory, there is an interpretation of the existence of electrical resistance of metals, that is, Ohm's and Joule-Lenz's laws. Classical electronic theory is unable to answer all questions.

It is unable to explain the difference in the value of the molar heat capacity of metals and dielectric crystals, equal to 3 R, where R is written as a universal gas constant. The heat capacity of a metal does not depend on the number of free electrons.

The classical electronic theory does not explain the temperature dependence of the resistivity of metals. According to the theory, ρ ~ T, and based on experiments, ρ ~ T. An example of a discrepancy between theory and practice is superconductivity.

Based on the classical theory, the resistivity of metals should gradually decrease with decreasing temperature, and it remains finite at any T. This dependence is typical for conducting experiments at high temperatures. If T is low enough, then the resistivity of metals loses its dependence on temperature and reaches a limiting value.

The phenomenon of superconductivity was of particular interest. In 1911 it was discovered by H. Kammerling Onnes.

Theorem 2

If there is a certain temperature T to p, different for different substances, then the resistivity decreases to zero with a jump, as shown in Figure 1. 12 . 4 .

Example 1

The critical temperature for mercury is considered to be 4.1 K, for aluminum - 1.2 K, for tin - 3.7 K. The presence of superconductivity can be not only in elements, but also in chemical compounds and alloys. Niobium with tin Ni 3 Sn have a critical temperature point of 18 K. There are substances that go into a superconducting state at low temperatures, whereas under normal conditions they are not. Silver and copper are conductors, but do not become superconductors when the temperature drops.

Picture 1 . 12 . 4 . Dependence of the resistivity ρ on the absolute temperature T at low temperatures: a - normal metal; b - superconductor.

The superconducting state speaks of the exceptional properties of the substance. One of the most important is the ability to maintain an electric current excited in a superconducting circuit for a long time without damping.

The classical electronic theory cannot explain superconductivity. This became possible 60 years after its discovery, based on quantum mechanical concepts.

The growth of interest in this phenomenon increased with the appearance of new materials capable of possessing high critical temperatures. In 1986, a complex compound was discovered with a temperature T to p \u003d 35 K. The next year they managed to create ceramics with a critical T of 98 K, which exceeded the T of liquid nitrogen (77 K).

Definition 7

The phenomenon of the transition of substances into a superconducting state at T exceeding the boiling point of liquid nitrogen is called high temperature superconductivity.

Later in 1988, they created a Tl - Ca - Ba - Cu - O compound with a critical T reaching 125 K. At the moment, scientists are interested in finding new substances with the highest values \u200b\u200bof T to p. They expect to get a superconducting substance at room temperature. If this is done, there will be a revolution in science and technology. Until now, all the properties and mechanisms of the composition of superconducting ceramic materials have not been fully investigated.

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Open lesson in physics in grade 8.

Topic “Electric current in metals. Electric current action. "

The purpose of the lesson: To continue the study of the nature of electric current in metals, experimentally study the action of electric current.

Lesson Objectives:

Educational -the formation of common views on the nature of electric current, the formation of the ability to work with electrical circuits, to collect electrical circuits.

Developing- the formation of the ability to find mistakes and avoid them when applying knowledge in practice, as well as to logically explain new phenomena, apply their knowledge in non-standard situations.

Educational -foster a feeling of love for their homeland, instill a love of fiction, the formation of the ability to concentrate attention, conduct a dialogue, and defend one's opinion with arguments.

Equipment and materials: current sources, an electric lamp for a flashlight, an electric bell, switches, supply wires, a solution of copper sulfate, an electromagnet, copper and zinc plates, a model of a crystal lattice, a galvanometer.

TSO: computer presentation, CD with software "Cyril and Methodius" Physics Grade 8, multimedia projector.

Demonstrations:

1) Assembly of the simplest electrical circuits.

2) Release of copper during CuSO4 electrolysis.

3) The action of a coil with a current, like an electromagnet.

4) Obtaining a power source using a lemon and a copper and zinc plate.

Lesson plan.

Basic knowledge update -10 min.

Study of new material "Electric current in metals" - 10 min

Fixing -3 min

One minute rest -1 min

Study of the new material "Actions of electric current". 12 minutes

Fixing -5 min.

Homework -2min.

Lesson summary -2 min.

During the classes.

1) Actualization of basic knowledge -10 min.

Hello guys, our lesson, I want to start with this quatrain:

How our planet would live

How people would live on it

Without heat, magnet, light

And electric rays.

Guys, knowledge of science always helps a person in life, and ignorance sometimes leads to tragic consequences. Draw the right conclusions for yourself from these words.

My quatrain mentions electric rays. What do you think it is? (electricity)

What is called electric shock?

Sample answer. Ordered directional movement of particles.

What is necessary for an electric current to exist in the circuit?

E. Answer... The current source, conductors, current consumer, and all these elements must be closed.

3) Working with diagrams.

Now let's check how you see violations in the drawing up of electrical circuits.

Here are two e-mails. circuits, diagrams of which are presented on the screen.

1. Why does the working lamp in the first circuit not light up when the key is closed? (Fig. 1)

Student response.

Sample answer. The electrical circuit is open. For the lamp to light up, an electric current must exist in the circuit, and this is possible with a closed circuit consisting only of electricity conductors.

Teacher.How do conductors differ from non-conductors or insulators?

Student response.

Sample answer. Conductors are bodies through which electric charges can pass from a charged body to an uncharged one. And in insulators, such transitions are impossible, and the lamp lights up.

The student is invited who gave the correct answer and he, having bridged the gap, demonstrates the correct answer. The lamp comes on.

2. Why does not the bell ring in the second circuit when the circuit is closed? (Fig. 2)

Student response.

Sample answer. To obtain an electric current in a conductor, an electric field must be created in it. Under the influence of this field, free charged particles will begin to move in an orderly manner, and this is an electric current. An electric field in conductors is created and can be maintained for a long time by sources of an electric field. The electrical circuit must have a current source. We connect the circuit to the current source and the bell rings.

A student is invited who gave the correct answer and, having connected a current source to the circuit, demonstrates the correct answer.

Encrypted word.

Guys, now let's read the encrypted word, but for this you need to remember the conventions used on the diagrams for electrical appliances. Put the letters in front of the corresponding devices and, starting with the arrow, read the word.

Slide number 4 Answer: "Ruzayevka"

Slide No. 5 "Ordinary Ruzayevka - the railway gate of Mordovia"

Slide 6 Objectives: For what purpose are thick copper bridges made at the joints of electrified railways or the rails are welded?

Answer. The rails conduct electric current and, therefore, to prevent the circuit from being open, copper jumpers are made or the rails are welded.

2. Learning new thingsmaterial "Electric current in metals" - 10 min .

Slide number 1 The topic of our lesson: “Electric current in metals. Electric current actions "

Guys, who knows how you can avoid the action of an electric current when you accidentally touch an electrical appliance that is energized?

Sample answer. This requires grounding, since the ground is a conductor and, due to its enormous size, can hold a large charge.

Teacher. What materials are used for grounding?

Student response.

Sample answer. Grounding is made of metal.

Teacher. Why these substances are preferred, we will answer after studying the new topic “Electric current in metals”. Write the lesson topic in your notebook.

So, our conversation will focus on metals. The most famous of the earliest definitions of metal was given in the middle of the 18th century by M.V. Lomonosov: “Metal is a light body that can be forged. There are only six such bodies: gold, silver, copper, tin, iron and lead. " After two and a half centuries, much has become known about metals. More than 75% of all elements in Mendeleev's table are metals, and it is almost a hopeless task to find an absolutely precise definition for metals.

Therefore, today, in the general case, you can use the definition of MV Lomonosov, the first Russian scientist - a naturalist of world significance, adding three more to the first two properties proposed by him. You will learn all the properties of metals. Let's start our acquaintance with one of them - electrical conductivity.

Let's remember the structure of metals. The model of a metal is a crystal lattice, in the nodes of which the particles perform chaotic oscillatory motion. (A model of a crystal lattice is presented, and an image of a model of the structure of metals is projected on the screen).

Metals in the solid state have a crystalline structure. Particles in crystals are arranged in a certain order, forming a spatial (crystal) lattice. As you already know, in any metal part of the valence electrons leave their places in the atom, as a result of which the atom turns into a positive ion. Positive ions are located in the nodes of the crystal lattice of the metal, and free electrons (electron gas) move in the space between them, i.e. not associated with the nuclei of their atoms.
The absolute value of the negative charge of all free electrons is equal to the positive charge of all ions in the lattice. Therefore, under normal conditions, the metal is electrically neutral.
What electric charges move under the action of an electric field in metal conductors? We can assume that free electrons move under the action of an electric field. But this assumption of ours needs proof.
In 1899, K. Ricke, at a tram substation in Stuttgart, connected three closely pressed cylinders to the main wire feeding the tram lines, in series with each other by their ends; the outer two were copper, and the middle one was aluminum.

Electric current passed through these cylinders for over a year. Having made a thorough analysis of the place where the cylinders were in contact, K. Ricke did not find aluminum atoms in copper, and copper atoms in aluminum, that is, diffusion did not occur. Thus, he experimentally proved that when an electric current passes through a conductor, ions do not move. Consequently, only free electrons move, and they are the same for all substances.

The final confirmation of this fact was the experiment carried out in 1913 by the physicists of our country L. I. Mandel'shtam and N. D. Papaleksi, as well as by the American physicists B. Stewart and R. Tolman. Check the drawing on the screen. Slide No.

electric current in metal conductors is the ordered movement of free electrons, under the influence of an electric field
If there is no electric field in the conductor, then electrons move chaotically, similar to how molecules of gases or liquids move. At each moment of time, the velocities of different electrons differ in modules and directions. If an electric field is created in the conductor, then the electrons, maintaining their chaotic motion, begin to shift towards the positive pole of the source. Along with the disordered movement of electrons, their ordered transfer also arises - drift.

The speed of the ordered movement of electrons in a conductor under the action of an electric field is several millimeters per second, and sometimes even less. But as soon as an electric field appears in a conductor, it spreads along the entire length of the conductor at a tremendous speed, close to the speed of light in a vacuum (300,000 km / s).
Simultaneously with the propagation of the electric field, all electrons begin to move in the same direction along the entire length of the conductor. So, for example, when the circuit of an electric lamp is closed, the electrons present in the lamp spiral also come into ordered motion.
This can be understood by comparing the electric current with the flow of water in a water supply system, and the propagation of an electric field with the propagation of water pressure. When water rises into the water tower, the pressure (pressure) of the water spreads very quickly throughout the water supply system. When we open the tap, the water is already under pressure and starts to flow. But the water that was in it flows from the tap, and the water from the tower will reach the tap much later, because the movement of water occurs at a lower speed than the propagation of pressure.
When we talk about the speed of propagation of an electric current in a conductor, we mean the speed of propagation of an electric field along the conductor.
An electrical signal sent, for example, by wires from Moscow to Vladivostok (s \u003d 8000 km), arrives there in about 0.03 s.

A minute of rest.

Guys, once the great thinker Socrates was asked what, in his opinion, is the easiest thing in life? He replied that the easiest thing is to teach others, and the hardest is to know oneself.

In physics lessons, we talk about knowing nature. But today, let's kick ourselves in. How do we perceive the world around us? As artists or as thinkers?

Stand up, put your hands up, stretch.

Interlace your fingers.

See which finger of your left or right hand is on top of you? Write down the result "L" or "P"

Cross your arms over your chest. ("Napoleon Pose") Which hand is on top?

Please applaud. Which hand is on top?

Let's summarize.

Considering that the result "LLL" corresponds to the artistic type of personality, and the "PPP" - to the type of thinking.

What type of thinking prevails in your class?

Several "artists", several "thinkers", and most of the guys are harmoniously developed personalities who are characterized by both logical and imaginative thinking.

And now you can proceed to the knowledge of the external world. Finished uh

Electric current in metals. We pass to the next block "Electric current actions"

Studying new material "Actions of electric current."

We cannot see electrons moving in a metal conductor. We can judge about the presence of current in a circuit by various phenomena that are caused by an electric current. Such phenomena are called the actions of the current. Some of these actions are easy to observe from experience.

Thermal effect of the current. (Slide №,) Program disk Physics lessons Grade 8 Vertual school of Cyril and Methodius. Lesson 08 (paragraph 7.9)

Chemical action of the current. Chemical action of el. current was first discovered in 1800.

Experience. Let's conduct an experiment with a solution of copper sulfate. We put two carbon electrodes in distilled water and close the circuit. We observe that El. the light does not light up. We take a solution of copper sulfate and connect it to a current source. The el light comes on.

Conclusion. Chemical the effect of the current is that in some solutions of acids (salts, alkalis), when an electric current passes through them, the release of substances is observed. The substances contained in the solution are deposited on the electrodes immersed in this solution. When current is passed through a solution of copper sulfate (CuSo4), pure copper (Cu) will be released on the negatively charged electrode. This is used to obtain pure metals.

Aluminum is obtained by electrolysis (this is the only industrial method for its production), chemical pure metals, nickel-plating, chromium plating, gilding.

To protect metals from corrosion, their surface is often coated with difficultly oxidized metals, i.e. nickel or chrome plating. This process is called electroplating.

Magnetic action of the current.

Experience. We connect the coil with an iron core to the circuit and observe the attraction of metal objects.

Using the magnetic action of current in galvanometers.

Slide #

Galvanometer. Schematic designation

Consolidation of the studied material.

TOthe Italian philosopher Confucius once said, as if for you and me

"It is good to have a natural gift, but exercise, friends, gives us more than a natural gift."

A Russian proverb says: "Learning is always useful."

Why shouldn't you touch bare electrical wires with your bare hands?

(The moisture on the hands always contains a solution of various salts and is an electrolyte. Therefore, it creates good contact between the wires and the skin.)

Guys, I'll read you an excerpt from the story of K.G. Paustovsky "Gift"

“The forester is a cunning man; when he lived in Moscow, they say, he used electric current to cook his own food. Could it be or not?

-Maybe, replied Reuben.

Maybe, maybe! - the children mimicked him. - Have you seen this electric current? How did you see him when he has no visibility, like air? "

? How would you explain to your grandfather what an electric current is? And how can you cook food with it?

Home assignment. Paragraph. 34.35L. No. 1260, 1261. Come up with a poem, or a riddle about email. current, or drawing.

Topic "Electric current in metals"

The purpose of the lesson: To continue the study of the nature of electric current in metals, experimentally study the action of electric current.

Lesson Objectives:

Educational -the formation of common views on the nature of electric current, the formation of the ability to work with electrical circuits, to collect electrical circuits.

Educational -the formation of the ability to concentrate attention, conduct a dialogue, defend one's opinion reasonably.

Equipment and materials: current sources, an electric lamp for a flashlight, an electric bell, switches, lead wires, a solution of copper sulphate, an electromagnet, copper and zinc plates, a model of a crystal lattice, a galvanometer.

TSO: computer presentation, multimedia projector.

Demonstrations:

1) Assembly of the simplest electrical circuits.

2) Release of copper during the electrolysis of copper sulfate

3) The action of a coil with a current, like an electromagnet.

Lesson plan.

Knowledge update (10 min).
Study of new material "Electric current in metals" (10 min)

"Actions of electric current" (12 min)

Fastening (9 min)
Homework (2min)
Summing up (2 min)

During the classes.

Hello guys!

How our planet would live

How people would live on it

Without heat, magnet, light

And electric rays.

This quatrain mentions electric rays. What do you think it is? (electricity)

1) What is called electric current?

2) What is necessary for an electric current to exist in the circuit?

3) Working with circuits: name the proposed main parts of the electrical circuit

Designations are proposed: electric lamp, key, ammeter, voltmeter, current source, calls, etc.

4) Now let's check how you see violations in the drawing up of electrical circuits.

Before you are two electrical circuits, diagrams of which are presented on the screen.

1. What violations have you noticed? Why does the working lamp in the first circuit not light up when the key is closed? Answer. The electrical circuit is open. For the lamp to light up, an electric current must exist in the circuit, and this is possible with a closed circuit consisting only of electricity conductors.

2) How are conductors different from non-conductors or insulators? Answer.Students bridge the gap. The lamp comes on.

2. Why does not the bell ring in the second circuit when the circuit is closed? Answer. To obtain an electric current in a conductor, an electric field must be created in it. Under the influence of this field, free charged particles will begin to move in an orderly manner, and this is an electric current. An electric field in conductors is created and can be maintained for a long time by sources of an electric field. The electrical circuit must have a current source. We connect the circuit to the current source and the bell rings. For the existence of an electric current, the following conditions are necessary: \u200b\u200b-------- the presence of free electric charges in the conductor; - the presence of an external electric field for the conductor. The student, by connecting a current source to the circuit, demonstrates the correct answer.

2. Learning new thingsmaterial "Electric current in metals" - 10 min . Slide number 1 The topic of our lesson: “Electric current in metals. Actions of electric current "Guys, who knows how you can avoid the action of electric current if you accidentally touch an electrical appliance that is energized? Answer. This requires grounding, since the ground is a conductor and, due to its enormous size, can hold a large charge. Teacher. What materials are used for grounding? Answer. Grounding is made of metal. Teacher. Why do they prefer metals? We will answer this question after studying the new topic “Electric current in metals”. Write the lesson topic in your notebook.

The most famous of the earliest definitions of metal was given in the middle of the 18th century by M.V. Lomonosov: “Metal is a light body that can be forged. There are only six such bodies: gold, silver, copper, tin, iron and lead. " After two and a half centuries, much has become known about metals. More than 75% of all elements of the DI Mendeleev's table are among the metals.

Today we will get acquainted with an important property of metals - electrical conductivity. Let's remember the structure of metals. Demonstrationmodel of the crystal lattice, the image of the model of the structure of metals is projected on the screen.

The model of a metal is a crystal lattice, in the nodes of which the particles perform chaotic oscillatory motion.

Free electrons move under the action of an electric field. The final confirmation of this fact was the experiment carried out in 1913 by the physicists of our country L. I. Mandel'shtam and N. D. Papaleksi, as well as by the American physicists B. Stewart and R. Tolman. Look at the picture on the screen

Thermal effect of the current.

Chemical action of the current. The chemical action of electric current was first discovered in 1800 Experience. Let's conduct an experiment with a solution of copper sulfate. We put two carbon electrodes in distilled water and close the circuit. We observe that the lamp does not light up. We take a solution of copper sulfate and connect it to a current source. The el light comes on. Conclusion. Chemical the effect of the current is that in some solutions of acids (salts, alkalis), when an electric current passes through them, the release of substances is observed. The substances contained in the solution are deposited on the electrodes immersed in this solution. When current is passed through a solution of copper sulfate (CuSO 4), pure copper (Cu) will be released on the negatively charged electrode. This is used to obtain pure metals. By electrolysis, aluminum, chemical pure metals are obtained, nickel plating, chromium plating, gilding are performed. To protect metals from corrosion, their surface is often coated with difficultly oxidized metals, i.e. nickel or chromium plating. This process is called electroplating. Guys, what methods of protecting metals from corrosion do you know?

the Itai philosopher Confucius once said "It's good to have a natural talent, but exercise, friends, gives us more than a natural talent." A Russian proverb says: “Learning will always come in handy.” 1) Why can't you touch bare electric wires with your bare hands? (The moisture on the hands always contains a solution of various salts and is an electrolyte. Therefore, it creates good contact between the wires and the skin.)

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Physics lesson in grade 8.

Topic "Electric current in metals"

The purpose of the lesson : To continue the study of the nature of electric current in metals, experimentally study the action of electric current.

Lesson Objectives:

Educational -the formation of common views on the nature of electric current, the formation of the ability to work with electrical circuits, to collect electrical circuits.

Developing - the formation of the ability to find mistakes and avoid them when applying knowledge in practice, as well as to logically explain new phenomena, apply their knowledge in non-standard situations.

Educational -the formation of the ability to concentrate attention, conduct a dialogue, defend one's opinion reasonably.

Equipment and materials: current sources, an electric lamp for a flashlight, an electric bell, switches, lead wires, a solution of copper sulphate, an electromagnet, copper and zinc plates, a model of a crystal lattice, a galvanometer.

TSO : computer presentation, multimedia projector.

Demonstrations:

1) Assembly of the simplest electrical circuits.

2) Release of copper during the electrolysis of copper sulfate

3) The action of a coil with a current, like an electromagnet.

Lesson plan.

Knowledge update (10 min).
Study of the new material "Electric current in metals" (10 min)

"Actions of electric current" (12 min)

Fastening (9 min)
Homework (2min)
Summing up (2 min)

During the classes.

Announcement of the topic, goals of the lesson.

1) Updating knowledge -10 min.

Hello guys!

How our planet would live

How people would live on it

Without heat, magnet, light

And electric rays.

This quatrain mentions electric rays. What do you think it is? (electricity)

Questions:

What is called electric shock?
What is necessary for an electric current to exist in the circuit?

3) Working with circuits: name the proposed main parts of the electrical circuit

Designations are proposed: an electric lamp, a key, an ammeter, a voltmeter, a current source, calls, etc.

4) Now let's check how you see violations in the drawing up of electrical circuits.

Before you are two electrical circuits, diagrams of which are presented on the screen.

1. What violations have you noticed? Why does the working lamp in the first circuit not light up when the key is closed?Answer. The electrical circuit is open. For the lamp to light up, an electric current must exist in the circuit, and this is possible with a closed circuit consisting only of electricity conductors.

2) How are conductors different from non-conductors or insulators?Answer. Students bridge the gap. The lamp comes on.

2. Why does not the bell ring in the second circuit when the circuit is closed?Answer. To obtain an electric current in a conductor, an electric field must be created in it. Under the influence of this field, free charged particles will begin to move in an orderly manner, and this is an electric current. An electric field in conductors is created and can be maintained for a long time by sources of an electric field. The electrical circuit must have a current source. We connect the circuit to the current source and the bell rings. For the existence of an electric current, the following conditions are necessary: \u200b\u200b-------- the presence of free electric charges in the conductor; - the presence of an external electric field for the conductor. The student, by connecting a current source to the circuit, demonstrates the correct answer.

2. Learning new thingsmaterial "Electric current in metals" - 10 min. Slide number 1 The topic of our lesson: “Electric current in metals. Actions of electric current "Guys, who knows how you can avoid the action of electric current if you accidentally touch an electrical appliance that is energized?Answer. This requires grounding, since the ground is a conductor and, due to its enormous size, can hold a large charge.Teacher. What materials are used for grounding?Answer. Grounding is made of metal.Teacher. Why do they prefer metals? We will answer this question after studying the new topic “Electric current in metals”. Write the lesson topic in your notebook.

Today we will get acquainted with an important property of metals - electrical conductivity. Let's remember the structure of metals.Demonstration model of the crystal lattice, the image of the model of the structure of metals is projected on the screen.

The model of a metal is a crystal lattice, in the nodes of which the particles perform chaotic oscillatory motion.

Metals in the solid state have a crystalline structure. Particles in crystals are arranged in a certain order, forming a spatial (crystal) lattice. As you already know, in any metal part of the valence electrons leave their places in the atom, as a result of which the atom turns into a positive ion. Positive ions are located at the nodes of the crystal lattice of the metal, and free electrons (electron gas) move in the space between them, i.e. not associated with the nuclei of their atoms.
The absolute value of the negative charge of all free electrons is equal to the positive charge of all ions in the lattice. Therefore, under normal conditions, the metal is electrically neutral.
What electric charges move under the action of an electric field in metal conductors? Free electrons move under the action of an electric field. The final confirmation of this fact was the experiment carried out in 1913 by the physicists of our country L. I. Mandel'shtam and N. D. Papaleksi, as well as by the American physicists B. Stewart and R. Tolman. Look at the picture on the screen

Scientists set a multi-turn coil in a very fast rotation around its axis. Then, with a sharp deceleration of the coil, its ends were closed to a galvanometer, and the device recorded a short-term electric current. The reason for the occurrence, which is caused by the inertial motion of free charged particles between the nodes of the crystal lattice of the metal. Since the direction of the initial velocity and the direction of the resulting current are known from experience, the sign of the charge of the carriers can be found: it turns out to be negative. Consequently, free charge carriers in a metal are free electrons. By the deflection of the galvanometer needle, one can judge the magnitude of the electric charge flowing in the circuit. Experience has confirmed the theory. The triumph of the classical theory of electricity took place.Electric current in metal conductors is the ordered movement of free electrons, under the influence of an electric field
If there is no electric field in the conductor, then electrons move chaotically, similar to how molecules of gases or liquids move. At each moment of time, the velocities of different electrons differ in modules and directions. If an electric field is created in the conductor, then the electrons, maintaining their chaotic motion, begin to shift towards the positive pole of the source. Along with the disordered movement of electrons, their ordered transfer also arises - drift. The speed of the ordered movement of electrons in a conductor under the action of an electric field is several millimeters per second, and sometimes even less. But as soon as an electric field appears in a conductor, it spreads along the entire length of the conductor at a tremendous speed, close to the speed of light in a vacuum (300,000 km / s).
Simultaneously with the propagation of the electric field, all electrons begin to move in the same direction along the entire length of the conductor. So, for example, when the circuit of an electric lamp is closed, the electrons present in the lamp spiral also come into ordered motion.
This can be understood by comparing the electric current with the flow of water in a water supply system, and the propagation of an electric field with the propagation of water pressure. When water rises into the water tower, the pressure (pressure) of the water spreads very quickly throughout the water supply system. When we open the tap, the water is already under pressure and starts to flow. But the water that was in it flows from the tap, and the water from the tower will reach the tap much later, because the movement of water occurs at a slower speed than the propagation of pressure.
When we talk about the speed of propagation of an electric current in a conductor, we mean the speed of propagation of an electric field along the conductor.
An electrical signal sent, for example, by wires from Moscow to Vladivostok (s \u003d 8000 km), arrives there in about 0.03 s. And now you can proceed to the knowledge of the external world. Finished electric current in metals. We pass to the next block "Electric current actions"

Study of new material "Actions of electric current"We cannot see electrons moving in a metal conductor. We can judge about the presence of current in a circuit by various phenomena that are caused by an electric current. Such phenomena are called the actions of the current. Some of these actions are easy to observe from experience.

Thermal effect of the current. Program disk Physics lessons Grade 8. Cyril and Methodius virtual school

Chemical action of the current.The chemical action of electric current was first discovered in 1800Experience. Let's conduct an experiment with a solution of copper sulfate. We put two carbon electrodes in distilled water and close the circuit. We observe that the lamp does not light up. We take a solution of copper sulfate and connect it to a current source. The el light comes on.Conclusion. Chemicalthe effect of the current is that in some solutions of acids (salts, alkalis), when an electric current passes through them, the release of substances is observed. The substances contained in the solution are deposited on the electrodes immersed in this solution. When passing current through a solution of copper sulfate (CuSO4 ) pure copper (Cu) will be released on the negatively charged electrode. This is used to obtain pure metals. By electrolysis, aluminum, chemical pure metals are obtained, nickel plating, chromium plating, gilding are performed. To protect metals from corrosion, their surface is often coated with difficultly oxidized metals, i.e. nickel or chromium plating. This process is called electroplating. Guys, what methods of protecting metals from corrosion do you know?

Magnetic action of the current. Experience. We connect the coil with an iron core to the circuit and observe the attraction of metal objects. Using the magnetic action of current in galvanometers. Galvanometer. Schematic designationConsolidation of the studied material. Questions on a new topic. TOthe Itai philosopher Confucius once said "It's good to have a natural talent, but exercise, friends, gives us more than a natural talent." A Russian proverb says: “Learning will always come in handy.” 1) Why can't you touch bare electric wires with your bare hands? (The moisture on the hands always contains a solution of various salts and is an electrolyte. Therefore, it creates good contact between the wires and the skin.)

Homework. P. 34.35L. No. 1260, 1261. Prepare a message about the metals "Aluminum", "Gold", "Iron"