How can you apply magnetic induction in everyday life. The phenomenon of electromagnetic current induction: the essence, who discovered

Exploring the emergence electric current has always been of concern to scientists. After in early XIX century, the Danish scientist Oersted found out that a magnetic field arises around an electric current, scientists wondered if a magnetic field could generate an electric current and vice versa. The first scientist who succeeded was the scientist Michael Faraday.

Faraday's experiments

After numerous experiments, Faraday was able to achieve some results.

1. The occurrence of electric current

To conduct the experiment, he took a coil with big amount turns and connected it to a milliammeter (a device that measures current). In the up and down direction, the scientist moved the magnet around the coil.

During the experiment, an electric current actually appeared in the coil due to a change in the magnetic field around it.

According to Faraday's observations, the milliammeter needle deviated and indicated that the movement of the magnet generates an electric current. When the magnet stopped, the arrow showed zero markings, i.e. no current circulates in the circuit.

rice. 1 Change in the current strength in the coil due to the movement of the rejctate

This phenomenon, in which the current occurs under the influence of an alternating magnetic field in the conductor, was called the phenomenon electromagnetic induction.

2.Changing the direction of the induction current

In his subsequent research, Michael Faraday tried to find out what influences the direction of the resulting inductive electric current. While conducting experiments, he noticed that by changing the number of coils on the coil or the polarity of the magnets, the direction of the electric current that occurs in a closed network changes.

3. The phenomenon of electromagnetic induction

To conduct the experiment, the scientist took two coils, which he placed close to each other. The first coil, having a large number of turns of wire, was connected to a current source and a key that closed and opened the circuit. He connected the second same coil to a milliammeter without being connected to a current source.

While conducting an experiment, Faraday noticed that when an electrical circuit is closed, an induced current occurs, which can be seen from the movement of the arrow of a milliammeter. When the circuit was opened, the milliammeter also showed that there was an electric current in the circuit, but the readings were exactly the opposite. When the circuit was closed and the current circulated evenly, there was no current in the electrical circuit according to the data of the milliammeter.

https://youtu.be/iVYEeX5mTJ8

Conclusion from experiments

As a result of Faraday's discovery, the following hypothesis was proved: electric current appears only when the magnetic field changes. It has also been proven that changing the number of turns in the coil changes the value of the current (increasing the coils increases the current). Moreover, an induced electric current can appear in a closed circuit only in the presence of an alternating magnetic field.

What determines the inductive electric current?

Based on all of the above, it can be noted that even if there is a magnetic field, it will not lead to the appearance of an electric current, if this field is not alternating.

So what does the magnitude of the induction field depend on?

1. The number of turns on the coil;
2. The rate of change of the magnetic field;
3. The speed of the magnet.

Magnetic flux is a quantity that characterizes a magnetic field. changing magnetic flux leads to a change in the induced electric current.

Fig. 2 Change in current strength when moving a) the coil in which the solenoid is located; b) a permanent magnet by inserting it into the coil

Faraday's Law

Based on the experiments, Michael Faraday formulated the law of electromagnetic induction. The law is that, when a magnetic field changes, it leads to the appearance of an electric current, while the current indicates the presence of an electromotive force of electromagnetic induction (EMF).

Speed magnetic current changing entails a change in the speed of the current and EMF.

Faraday's Law: The EMF of electromagnetic induction is numerically equal and opposite in sign to the rate of change of magnetic flux that passes through a surface bounded by a contour

Loop inductance. Self-induction.

A magnetic field is created when current flows in a closed circuit. In this case, the current strength affects the magnetic flux and induces an EMF.

Self-induction is a phenomenon in which the induction emf occurs when the current strength in the circuit changes.

Self-induction varies depending on the features of the shape of the circuit, its dimensions and the environment containing it.

As the electric current increases, the self-inductive current of the loop can slow it down. When it decreases, the self-induction current, on the contrary, does not allow it to decrease so quickly. Thus, the circuit begins to have its electrical inertia, slowing down any change in current.

Application of induced emf

The phenomenon of electromagnetic induction has a practical application in generators, transformers and motors running on electricity.

In this case, the current for these purposes is obtained in the following ways:

1. Change of current in the coil;
2. The movement of the magnetic field through permanent magnets and electromagnets;
3. The rotation of coils or coils in a constant magnetic field.

The discovery of electromagnetic induction by Michael Faraday made a great contribution to science and to our everyday life. This discovery served as an impetus for further discoveries in the field of studying electromagnetic fields and is widely used in modern life of people.

After the discoveries of Oersted and Ampère, it became clear that electricity has a magnetic force. Now it was necessary to confirm the influence magnetic phenomena to electric. This problem was brilliantly solved by Faraday.

In 1821, M. Faraday made an entry in his diary: "Turn magnetism into electricity." After 10 years, this problem was solved by him.

So, Michael Faraday (1791-1867) - English physicist and chemist.

One of the founders of quantitative electrochemistry. First received (1823) in liquid state chlorine, then hydrogen sulfide, carbon dioxide, ammonia and nitrogen dioxide. Discovered (1825) benzene, studied its physical and some Chemical properties. Introduced the concept of dielectric permittivity. Faraday's name entered the system of electrical units as a unit of electrical capacitance.

Many of these works could, by themselves, immortalize the name of their author. But the most important of scientific works Faraday are his research in the field of electromagnetism and electrical induction. Strictly speaking, the important branch of physics, which treats the phenomena of electromagnetism and inductive electricity, and which is currently of such great importance for technology, was created by Faraday out of nothing.

When Faraday finally devoted himself to research in the field of electricity, it was found that with ordinary conditions the presence of an electrified body is sufficient for its influence to excite electricity in every other body.

At the same time, it was known that the wire through which the current passes and which is also an electrified body does not have any effect on other wires placed nearby. What caused this exception? This is the question that interested Faraday and the solution of which led him to major discoveries in the field of induction electricity.

Faraday wound two insulated wires parallel to each other on the same wooden rolling pin. He connected the ends of one wire to a battery of ten elements, and the ends of the other to a sensitive galvanometer. When the current was passed through the first wire, Faraday turned all his attention to the galvanometer, expecting to notice from its oscillations the appearance of a current in the second wire. However, there was nothing of the kind: the galvanometer remained calm. Faraday decided to increase the current and introduced 120 galvanic cells into the circuit. The result is the same. Faraday repeated this experiment dozens of times, all with the same success. Anyone else in his place would have left the experiment, convinced that the current passing through the wire has no effect on the adjacent wire. But Faraday always tried to extract from his experiments and observations everything that they could give, and therefore, not having received a direct effect on the wire connected to the galvanometer, he began to look for side effects.

electromagnetic induction electric current field

He immediately noticed that the galvanometer, remaining completely calm during the entire passage of the current, began to oscillate at the very closing of the circuit, and when it was opened, it turned out that at the moment when the current was passed into the first wire, and also when this transmission ceased, during the second wire is also excited by a current, which in the first case has the opposite direction with the first current and is the same with it in the second case and lasts only one instant.

Being instantaneous, instantly disappearing after their appearance, inductive currents would have no practical significance if Faraday had not found a way, with the help of an ingenious device (commutator), to constantly interrupt and again conduct the primary current coming from the battery through the first wire, due to which in the second wire is continuously excited by more and more inductive currents, thus becoming constant. So a new source was found electrical energy, in addition to previously known (friction and chemical processes), - induction, and the new kind of this energy is induction electricity.

ELECTROMAGNETIC INDUCTION(lat. inductio - guidance) - the phenomenon of generating a vortex electric field variables magnetic field. If you introduce a closed conductor into an alternating magnetic field, then an electric current will appear in it. The appearance of this current is called current induction, and the current itself is called inductive.

Topic: The use of electromagnetic induction

Lesson Objectives:

Educational:

1. Continue work on the formation of the concept of the electromagnetic field as a form of matter and evidence of its real existence.
2. Improve skills in solving qualitative and computational problems.

Developing: Continue to work with students on...

1. formation of ideas about modern physical picture of the world,
2. the ability to reveal the relationship between the studied material and phenomena of life,
3. expanding the horizons of students

Educational: Learn to see the manifestations of the studied patterns in the surrounding life

Demonstrations

1. Transformer
2. Fragments of the CD-ROM “Physics grades 7-11. Library visual aids»

1) "Power generation"
2) "Recording and reading information on a magnetic tape"

3. Presentations

1) "Electromagnetic induction - tests" (parts I and II)
2) "Transformer"

During the classes

1. Update:

Before considering new material please answer the following questions:

2. Problem solving on cards, see presentation (Appendix 1) (answers: 1 B, 2 B, 3 C, 4 A, 5 C) - 5 min

3. New material.

The use of electromagnetic induction

1) In the past academic year when studying the topic “Information Carriers” in computer science, we talked about disks, floppy disks, etc. It turns out that the recording and reading of information using a magnetic tape is based on the application of the phenomenon of electromagnetic induction.
Recording and playback of information using a magnetic tape (Fragments of the CD-ROM "Physics grades 7-11. Library of visual aids", "Recording and reading information on a magnetic tape" - 3 min) (Appendix 2)

2) Consider the device and the fundamental operation of such a device as a TRANSFORMER. (See presentation Appendix 3)
The action of the transformer is based on the phenomenon of electromagnetic induction.

TRANSFORMER - a device that converts alternating current of one voltage into alternating current of another voltage at a constant frequency.

3) In the simplest case, the transformer consists of a closed steel core, on which two coils with wire windings are put on. That of the windings that is connected to an alternating voltage source is called primary, and the one to which the "load" is connected, that is, devices that consume electricity, is called secondary.

a) step up transformer

b) step down transformer

When transmitting energy over a long distance - the use of step-down and step-up transformers.

4) The work of the transformer (experiment).

Illumination of a light bulb in the secondary coil ( explanation of this experience);
- principle of operation welding machine (Why are the turns in the secondary coil of a step-down transformer thicker?);
- the principle of operation of the furnace ( The power in both coils is the same, but the current?)

5) Practical use electromagnetic induction

Examples technical use electromagnetic induction: transformer, electric current generator - the main source of electricity.
Thanks to the discovery of electromagnetic induction, it became possible to generate cheap electrical energy. The basis of the operation of modern power plants (including nuclear ones) is induction generator.
Generator alternating current(fragment of the CD Fragments of the CD-ROM "Physics grades 7-11. Library of visual aids", "Power generation" - 2 min) (Appendix 4)

The induction generator consists of two parts: a movable rotor and a fixed stator. Most often, the stator is a magnet (permanent or electric) that creates an initial magnetic field (it is called an inductor). The rotor consists of one or more windings, in which, under the action of a changing magnetic field, induction current. (Another name for such a rotor is an anchor).

- detection of metal objects - special detectors;
- train on magnetic cushions(see p. 129 of the textbook V. A. Kasyanov "Physics - 11")
Foucault currents (eddy currents;)
– closed induction currents arising in massive conducting bodies.

They appear either due to a change in the magnetic field in which the conducting body is located, or as a result of such a movement of the body when the magnetic flux penetrating this body (or any part of it) changes.
Like any other currents, eddy currents have a thermal effect on the conductor: the bodies in which such currents occur heat up.

Example: installation of electric furnaces for melting metals and microwave ovens.

4. Conclusions, assessments.

1) Electromagnetic induction, give examples of the practical application of electromagnetic induction.
2) Electromagnetic waves are the most common type of matter, and electromagnetic induction is special case manifestations of electromagnetic waves.

5. Solving problems on cards, see the presentation(Appendix 5) (answers - 1B, 2A, 3A, 4B).

6. House assignment: P.35,36 (Textbook of physics, edited by V.A.Kasyanov Grade 11)

The word "induction" in Russian means the processes of excitation, guidance, creation of something. In electrical engineering, this term has been used for more than two centuries.

After getting acquainted with the publications of 1821, describing the experiments of the Danish scientist Oersted on the deviations of a magnetic needle near a conductor with electric current, Michael Faraday set himself the task: convert magnetism to electricity.

After 10 years of research, he formulated the basic law of electromagnetic induction, explaining that inside any closed circuit, an electromotive force is induced. Its value is determined by the rate of change of the magnetic flux penetrating the circuit under consideration, but taken with a minus sign.

Transmission of electromagnetic waves over a distance

The first guess that dawned on the brain of a scientist was not crowned with practical success.

He placed two closed conductors side by side. Near one I installed a magnetic needle as an indicator of the passing current, and in the other wire I applied a pulse from a powerful galvanic source of that time: a volt column.

The researcher assumed that with a current pulse in the first circuit, the changing magnetic field in it would induce a current in the second conductor, which would deflect the magnetic needle. But, the result was negative - the indicator did not work. Or rather, he lacked sensitivity.

The scientist's brain foresaw the creation and transmission of electromagnetic waves over a distance, which are now used in radio broadcasting, television, wireless control, Wi-Fi technologies and similar devices. He was simply let down by an imperfect elemental base measuring devices that time.

Power generation

After an unsuccessful experiment, Michael Faraday modified the conditions of the experiment.

For the experiment, Faraday used two coils with closed circuits. In the first circuit, he supplied an electric current from a source, and in the second he observed the appearance of an EMF. The current passing through the turns of winding No. 1 created a magnetic flux around the coil, penetrating winding No. 2 and forming an electromotive force in it.

During Faraday's experiment:

• turned on the pulse supply of voltage to the circuit with stationary coils;
• when the current was applied, he injected the upper one into the lower coil;
• permanently fixed winding No. 1 and introduced winding No. 2 into it;
• change the speed of movement of the coils relative to each other.

In all these cases, he observed the manifestation of the induction emf in the second coil. And only when passing direct current there was no electromotive force on winding No. 1 and fixed coils.

The scientist determined that the EMF induced in the second coil depends on the speed at which the magnetic flux changes. It is proportional to its size.

The same pattern is fully manifested when a closed loop passes through. Under the action of the EMF, an electric current is formed in the wire.

The magnetic flux in the case under consideration changes in the circuit Sk created by a closed circuit.

In this way, the development created by Faraday made it possible to place a rotating conductive frame in a magnetic field.

She was then made from a large number turns, fixed in rotation bearings. At the ends of the winding, slip rings and brushes sliding along them were mounted, and a load was connected through the leads on the case. It turned out modern generator alternating current.

Its over simple design was created when the winding was fixed on a stationary case, and the magnetic system began to rotate. In this case, the method of generating currents at the expense was not violated in any way.

The principle of operation of electric motors

The law of electromagnetic induction, which was substantiated by Michael Faraday, made it possible to create various designs electric motors. They have a similar device with generators: a movable rotor and a stator, which interact with each other due to rotating electromagnetic fields.

Electricity transformation

Michael Faraday determined the occurrence of an induced electromotive force and an induction current in a nearby winding when the magnetic field in an adjacent coil changes.

The current inside the nearby winding is induced by switching the switch circuit in coil 1 and is always present during the operation of the generator on winding 3.

On this property, called mutual induction, the operation of all modern transformer devices is based.

To improve the passage of the magnetic flux, they have insulated windings put on a common core, which has a minimum magnetic resistance. It is made from special varieties steel and form typesetting thin sheets in the form of sections of a certain shape, called a magnetic circuit.

Transformers transmit, due to mutual induction, the energy of an alternating electromagnetic field from one winding to another in such a way that a change occurs, a transformation of the voltage value at its input and output terminals.

The ratio of the number of turns in the windings determines transformation ratio, and the thickness of the wire, the design and volume of the core material - the amount of transmitted power, the operating current.

Work of inductors

The manifestation of electromagnetic induction is observed in the coil during a change in the magnitude of the current flowing in it. This process is called self-induction.

When the switch is turned on in the above diagram, the inductive current modifies the nature of the rectilinear increase in the operating current in the circuit, as well as during the shutdown.

When an alternating voltage, not a constant voltage, is applied to a conductor wound into a coil, the current value reduced by the inductive resistance flows through it. The energy of self-induction shifts the phase of the current with respect to the applied voltage.

This phenomenon is used in chokes, which are designed to reduce the high currents that occur under certain operating conditions of the equipment. Such devices, in particular, are used.

Design feature of the magnetic circuit at the inductor - a cut of the plates, which is created to further increase the magnetic resistance to the magnetic flux due to the formation of an air gap.

Chokes with a split and adjustable position of the magnetic circuit are used in many radio engineering and electrical devices. Quite often they can be found in designs welding transformers. They reduce the size electric arc passed through the electrode to the optimum value.

Induction Furnaces

The phenomenon of electromagnetic induction manifests itself not only in wires and windings, but also inside any massive metal objects. The currents induced in them are called eddy currents. During the operation of transformers and chokes, they cause heating of the magnetic circuit and the entire structure.

To prevent this phenomenon, the cores are made of thin metal sheets and isolate each other with a layer of varnish that prevents the passage of induced currents.

In heating structures, eddy currents do not limit, but create the most favorable conditions. widely used in industrial production to create high temperatures.

Electrical measuring devices

A large class of induction devices continues to operate in the energy sector. Electric meters with a rotating aluminum disk, similar to the design of the power relay, resting systems of switch measuring instruments operate on the principle of electromagnetic induction.

Gas magnetic generators

If, instead of a closed frame, a conductive gas, liquid or plasma is moved in the field of a magnet, then the charges of electricity under the action of magnetic field lines will deviate in strictly defined directions, forming an electric current. Its magnetic field on the mounted electrode contact plates induces an electromotive force. Under its action, an electric current is created in the connected circuit to the MHD generator.

This is how the law of electromagnetic induction manifests itself in MHD generators.

There are no such complex rotating parts as the rotor. This simplifies the design, allows you to significantly increase the temperature working environment and, at the same time, the efficiency of power generation. MHD generators operate as backup or emergency sources capable of generating significant electricity flows in short periods of time.

Thus, the law of electromagnetic induction, justified by Michael Faraday at one time, continues to be relevant today.

abstract

in the discipline "Physics"

Topic: "Discovery of the phenomenon of electromagnetic induction"

Completed:

Student group 13103/1

St. Petersburg

2. Experiments of Faraday. 3

3. Practical application of the phenomenon of electromagnetic induction. nine

4. List of used literature .. 12

Electromagnetic induction - the phenomenon of the occurrence of an electric current in a closed circuit when the magnetic flux passing through it changes. Electromagnetic induction was discovered by Michael Faraday on August 29, 1831. He found that the electromotive force that occurs in a closed conducting circuit is proportional to the rate of change of the magnetic flux through the surface bounded by this circuit. The magnitude of the electromotive force (EMF) does not depend on what causes the change in the flux - a change in the magnetic field itself or the movement of a circuit (or part of it) in a magnetic field. The electric current caused by this EMF is called the induction current.

In 1820, Hans Christian Oersted showed that an electric current flowing through a circuit causes a magnetic needle to deflect. If an electric current generates magnetism, then the appearance of an electric current must be associated with magnetism. This idea captured the English scientist M. Faraday. “Turn magnetism into electricity,” he wrote in 1822 in his diary.

Michael Faraday

Michael Faraday (1791-1867) was born in London, one of the poorest parts of it. His father was a blacksmith, and his mother was the daughter of a tenant farmer. When Faraday reached school age, he was sent to elementary school. The course taken by Faraday here was very narrow and limited only to teaching reading, writing, and the beginning of counting.

A few steps from the house where the Faraday family lived, there was a bookstore, which was also a bookbinding establishment. This is where Faraday got to, having completed the course elementary school when the question arose about choosing a profession for him. Michael at that time was only 13 years old. Already in his youth, when Faraday had just begun his self-education, he strove to rely solely on facts and verify the reports of others with his own experiences.

These aspirations dominated him all his life as the main features of his scientific activity Physical and chemical experiments Faraday began to do it as a boy at the first acquaintance with physics and chemistry. Once Michael attended one of the lectures of Humphry Davy, the great English physicist. Faraday made a detailed note of the lecture, bound it, and sent it to Davy. He was so impressed that he offered Faraday to work with him as a secretary. Soon Davy went on a trip to Europe and took Faraday with him. For two years they visited the largest European universities.

Returning to London in 1815, Faraday began working as an assistant in one of the laboratories of the Royal Institution in London. At that time it was one of the best physics laboratories in the world. From 1816 to 1818 Faraday published a number of small notes and small memoirs on chemistry. Faraday's first work on physics dates back to 1818.

Based on the experiences of their predecessors and combining several own experiences, by September 1821 Michael had printed "The Success Story of Electromagnetism". Already at that time, he made up a completely correct concept of the essence of the phenomenon of deflection of a magnetic needle under the action of a current.

Having achieved this success, Faraday left his studies in the field of electricity for ten years, devoting himself to the study of a number of subjects of a different kind. In 1823, Faraday made one of the most important discoveries in the field of physics - he first achieved the liquefaction of a gas, and at the same time established a simple but valid method for converting gases into a liquid. In 1824, Faraday made several discoveries in the field of physics. Among other things, he established the fact that light affects the color of glass, changing it. IN next year Faraday again turns from physics to chemistry, and the result of his work in this area is the discovery of gasoline and sulfuric naphthalene acid.

In 1831, Faraday published a treatise On a Special Kind of Optical Illusion, which served as the basis for a beautiful and curious optical projectile called the "chromotrope". In the same year, another treatise by the scientist "On vibrating plates" was published. Many of these works could by themselves immortalize the name of their author. But the most important of Faraday's scientific works are his researches in the field of electromagnetism and electric induction.

Faraday's experiments

Obsessed with ideas about the inseparable connection and interaction of the forces of nature, Faraday tried to prove that just as Ampère could create magnets with electricity, so it is possible to create electricity with the help of magnets.

Its logic was simple: mechanical work easily turns into heat; Conversely, heat can be converted into mechanical work(let's say in steam engine). In general, among the forces of nature, the following relationship most often occurs: if A gives birth to B, then B gives birth to A.

If by means of electricity Ampère obtained magnets, then, apparently, it is possible to "obtain electricity from ordinary magnetism." Arago and Ampère set themselves the same task in Paris, Colladon in Geneva.

Strictly speaking, the important branch of physics, which treats the phenomena of electromagnetism and inductive electricity, and which is currently of such great importance for technology, was created by Faraday out of nothing. By the time Faraday finally devoted himself to research in the field of electricity, it was established that, under ordinary conditions, the presence of an electrified body is sufficient for its influence to excite electricity in any other body. At the same time, it was known that the wire through which the current passes and which is also an electrified body does not have any effect on other wires placed nearby.

What caused this exception? This is the question that interested Faraday and the solution of which led him to the most important discoveries in the field of induction electricity. Faraday puts on a lot of experiments, keeps pedantic notes. He devotes a paragraph to each small study in his laboratory notes (published in London in full in 1931 under the title "Faraday's Diary"). At least the fact that the last paragraph of the Diary is marked with the number 16041 speaks of Faraday's efficiency.

In addition to an intuitive conviction in the universal connection of phenomena, nothing, in fact, supported him in his search for "electricity from magnetism". In addition, he, like his teacher Devi, relied more on his own experiments than on mental constructions. Davy taught him:

“A good experiment has more value than the thoughtfulness of a genius like Newton.

Nevertheless, it was Faraday who was destined for great discoveries. A great realist, he spontaneously tore the fetters of empiricism, once imposed on him by Devi, and in those moments a great insight dawned on him - he acquired the ability for the deepest generalizations.

The first glimmer of luck appeared only on August 29, 1831. On this day, Faraday was testing a simple device in the laboratory: an iron ring about six inches in diameter, wrapped around two pieces of insulated wire. When Faraday connected a battery to the terminals of one winding, his assistant, artillery sergeant Andersen, saw the needle of a galvanometer connected to the other winding twitch.

She twitched and calmed down, although the direct current continued to flow through the first winding. Faraday carefully reviewed all the details of this simple installation - everything was in order.

But the galvanometer needle stubbornly stood at zero. Out of annoyance, Faraday decided to turn off the current, and then a miracle happened - during the opening of the circuit, the galvanometer needle swung again and again froze at zero!

The galvanometer, remaining perfectly still during the entire passage of the current, begins to oscillate when the circuit is closed and when it is opened. It turned out that at the moment when a current is passed into the first wire, and also when this transmission stops, a current is also excited in the second wire, which in the first case has the opposite direction with the first current and is the same with it in the second case and lasts only one instant.

It was here that Ampere's great ideas, the connection between electric current and magnetism, were revealed in all clarity to Faraday. After all, the first winding into which he applied current immediately became a magnet. If we consider it as a magnet, then the experiment on August 29 showed that magnetism seemed to give rise to electricity. Only two things remained strange in this case: why did the surge of electricity when the electromagnet was turned on quickly fade away? And moreover, why does the surge appear when the magnet is turned off?

The next day, August 30, - New episode experiments. The effect is clearly expressed, but nevertheless completely incomprehensible.

Faraday feels that the opening is somewhere nearby.

“I am now again engaged in electromagnetism and I think that I have attacked a successful thing, but I cannot yet confirm this. It may very well be that after all my labors, I will eventually pull out seaweed instead of fish.

By the next morning, September 24, Faraday had prepared a lot various devices, in which the main elements were no longer windings with electric current, but permanent magnets. And there was an effect too! The arrow deviated and immediately rushed into place. This slight movement occurred during the most unexpected manipulations with the magnet, sometimes, it seemed, by chance.

The next experiment is October 1st. Faraday decides to return to the very beginning - to two windings: one with a current, the other connected to a galvanometer. The difference with the first experiment is the absence of a steel ring - the core. The splash is almost imperceptible. The result is trivial. It is clear that a magnet without a core is much weaker than a magnet with a core. Therefore, the effect is less pronounced.

Faraday is disappointed. For two weeks he does not approach the instruments, thinking about the reasons for the failure.

"I took a cylindrical magnetic bar (3/4" in diameter and 8 1/4" long) and inserted one end of it into a spiral of copper wire(220 feet long) connected to a galvanometer. Then, with a quick movement, I pushed the magnet into the entire length of the spiral, and the needle of the galvanometer experienced a shock. Then I just as quickly pulled the magnet out of the spiral, and the needle swung again, but in the opposite direction. These swings of the needle were repeated each time the magnet was pushed in or out."

The secret is in the movement of the magnet! The impulse of electricity is determined not by the position of the magnet, but by the movement!

This means that "an electric wave arises only when the magnet moves, and not due to the properties inherent in it at rest."

Rice. 2. Faraday's experiment with a coil

This idea is remarkably fruitful. If the movement of a magnet relative to a conductor creates electricity, then, apparently, the movement of a conductor relative to a magnet must also generate electricity! Moreover, this "electric wave" will not disappear as long as the mutual movement of the conductor and the magnet continues. This means that it is possible to create an electric current generator that operates for an arbitrarily long time, as long as the mutual movement of the wire and the magnet continues!

On October 28, Faraday installed a rotating copper disk between the poles of a horseshoe magnet, from which electrical voltage could be removed using sliding contacts (one on the axis, the other on the periphery of the disk). It was the first electrical generator created by human hands. Thus, a new source of electrical energy was found, in addition to the previously known (friction and chemical processes), - induction, and a new type of this energy - induction electricity.

Experiments similar to Faraday's, as already mentioned, were carried out in France and Switzerland. Colladon, a professor at the Geneva Academy, was a sophisticated experimenter (he, for example, produced on Lake Geneva accurate measurements speed of sound in water). Perhaps, fearing the shaking of the instruments, he, like Faraday, removed the galvanometer as far as possible from the rest of the installation. Many claimed that Colladon observed the same fleeting movements of the arrow as Faraday, but, expecting a more stable, lasting effect, did not attach due importance to these “random” bursts ...

Indeed, the opinion of most scientists of that time was that the reverse effect of “creating electricity from magnetism” should, apparently, have the same stationary character as the “direct” effect - “forming magnetism” due to electric current. The unexpected "transience" of this effect baffled many, including Colladon, and these many paid for their prejudice.

Continuing his experiments, Faraday further discovered that a simple approximation of a wire twisted into a closed curve to another, along which a galvanic current flows, is enough to excite an inductive current in the direction opposite to the galvanic current in a neutral wire, that the removal of a neutral wire again excites an inductive current in it. the current is already in the same direction as the galvanic current flowing along a fixed wire, and that, finally, these inductive currents are excited only during the approach and removal of the wire to the conductor of the galvanic current, and without this movement, the currents are not excited, no matter how close the wires are to each other .

Thus, a new phenomenon was discovered, similar to the above-described phenomenon of induction during the closing and termination of the galvanic current. These discoveries in turn gave rise to new ones. If it is possible to produce an inductive current by closing and stopping the galvanic current, would not the same result be obtained from the magnetization and demagnetization of iron?

The work of Oersted and Ampère had already established the relationship between magnetism and electricity. It was known that iron becomes a magnet when an insulated wire is wound around it and a galvanic current passes through the latter, and that magnetic properties of this iron cease as soon as the current stops.

Based on this, Faraday came up with this kind of experiment: two insulated wires were wound around an iron ring; moreover, one wire was wound around one half of the ring, and the other around the other. A current from a galvanic battery was passed through one wire, and the ends of the other were connected to a galvanometer. And so, when the current closed or stopped, and when, consequently, the iron ring was magnetized or demagnetized, the galvanometer needle oscillated rapidly and then quickly stopped, that is, all the same instantaneous inductive currents were excited in the neutral wire - this time: already under the influence of magnetism.

Rice. 3. Faraday's experiment with an iron ring

Thus, here, for the first time, magnetism was converted into electricity. Having received these results, Faraday decided to diversify his experiments. Instead of an iron ring, he began to use an iron band. Instead of exciting magnetism in iron with a galvanic current, he magnetized the iron by touching it to a permanent steel magnet. The result was the same: in the wire wrapped around the iron, a current was always excited at the moment of magnetization and demagnetization of the iron. Then Faraday introduced a steel magnet into the wire spiral - the approach and removal of the latter caused induction currents in the wire. In a word, magnetism, in the sense of excitation of inductive currents, acted in exactly the same way as the galvanic current.

At that time, physicists were intensely occupied with one mysterious phenomenon discovered in 1824 by Arago and did not find an explanation, despite the fact that such outstanding scientists of that time as Arago himself, Ampère, Poisson, Babaj and Herschel were intensively looking for this explanation. The matter was as follows. A magnetic needle, freely hanging, quickly comes to rest if a circle of non-magnetic metal is brought under it; if the circle is then put into rotational motion, the magnetic needle begins to follow it.

In a calm state, it was impossible to discover the slightest attraction or repulsion between the circle and the arrow, while the same circle, which was in motion, pulled behind it not only a light arrow, but also a heavy magnet. This truly miraculous phenomenon seemed to the scientists of that time a mysterious riddle, something beyond the natural. Faraday, based on his above data, made the assumption that a circle of non-magnetic metal, under the influence of a magnet, is circulated during rotation by inductive currents that affect the magnetic needle and draw it behind the magnet. Indeed, by introducing the edge of the circle between the poles of a large horseshoe-shaped magnet and connecting the center and edge of the circle with a galvanometer with a wire, Faraday received a constant electric current during the rotation of the circle.

Following this, Faraday settled on another phenomenon that was then causing general curiosity. As you know, if iron filings are sprinkled on a magnet, they are grouped along certain lines, called magnetic curves. Faraday, drawing attention to this phenomenon, gave the foundations in 1831 to magnetic curves, the name "lines of magnetic force", which then came into general use. The study of these "lines" led Faraday to a new discovery, it turned out that for the excitation of inductive currents, the approach and removal of the source from the magnetic pole is not necessary. To excite currents, it is enough to cross the lines of magnetic force in a known way.

Rice. 4. "Lines of magnetic force"

Further work Faraday in the aforementioned direction acquired, from the contemporary point of view, the character of something completely miraculous. At the beginning of 1832, he demonstrated an apparatus in which inductive currents were excited without the help of a magnet or galvanic current. The device consisted of an iron strip placed in a wire coil. This device, under ordinary conditions, did not give the slightest sign of the appearance of currents in it; but as soon as he was given a direction corresponding to the direction of the magnetic needle, a current was excited in the wire.

Then Faraday gave the position of the magnetic needle to one coil and then introduced an iron strip into it: the current was again excited. The reason that caused the current in these cases was terrestrial magnetism, which caused inductive currents like an ordinary magnet or galvanic current. In order to show and prove this more clearly, Faraday undertook another experiment that fully confirmed his ideas.

He reasoned that if a circle of non-magnetic metal, for example, copper, rotating in a position in which it intersects the lines of magnetic force of a neighboring magnet, gives an inductive current, then the same circle, rotating in the absence of a magnet, but in a position in which the circle will cross the lines of terrestrial magnetism, must also give an inductive current. And indeed, a copper circle, rotated in a horizontal plane, gave an inductive current, which produced a noticeable deviation of the galvanometer needle. Faraday completed a series of studies in the field of electrical induction with the discovery, made in 1835, of "the inductive effect of current on itself."

He found out that when a galvanic current is closed or opened, instantaneous inductive currents are excited in the wire itself, which serves as a conductor for this current.

The Russian physicist Emil Khristoforovich Lenz (1804-1861) gave a rule for determining the direction of the induced current. “The induction current is always directed in such a way that the magnetic field it creates impedes or slows down the movement that causes induction,” notes A.A. Korobko-Stefanov in his article on electromagnetic induction. - For example, when the coil approaches the magnet, the resulting inductive current has such a direction that the magnetic field created by it will be opposite to the magnetic field of the magnet. As a result, repulsive forces arise between the coil and the magnet. Lenz's rule follows from the law of conservation and transformation of energy. If induction currents accelerated the movement that caused them, then work would be created from nothing. The coil itself, after a small push, would rush towards the magnet, and at the same time the induction current would release heat in it. In reality, the induction current is created due to the work of bringing the magnet and coil closer together.

Rice. 5. Lenz's rule

Why is there an induced current? A deep explanation of the phenomenon of electromagnetic induction was given by the English physicist James Clerk Maxwell, the creator of a complete mathematical theory of the electromagnetic field. To better understand the essence of the matter, consider a very simple experiment. Let the coil consist of one turn of wire and be pierced by an alternating magnetic field perpendicular to the plane of the turn. In the coil, of course, there is an induction current. Maxwell interpreted this experiment with exceptional courage and unexpectedness.

When the magnetic field changes in space, according to Maxwell, a process arises for which the presence of a wire coil is of no importance. The main thing here is the appearance of closed ring lines of the electric field, covering the changing magnetic field. Under the action of the emerging electric field, electrons begin to move, and an electric current arises in the coil. A coil is just a device that allows you to detect electric field. The essence of the phenomenon of electromagnetic induction is that an alternating magnetic field always generates in the surrounding space an electric field with closed lines of force. Such a field is called a vortex field.

Research in the field of induction produced by terrestrial magnetism gave Faraday the opportunity to express the idea of ​​a telegraph as early as 1832, which then formed the basis of this invention. In general, the discovery of electromagnetic induction is not without reason attributed to the most outstanding discoveries XIX century - the work of millions of electric motors and electric current generators around the world is based on this phenomenon ...

Practical application of the phenomenon of electromagnetic induction

1. Broadcasting

An alternating magnetic field, excited by a changing current, creates an electric field in the surrounding space, which in turn excites a magnetic field, and so on. Mutually generating each other, these fields form a single variable electromagnetic field - electromagnetic wave. Having arisen in the place where there is a wire with current, the electromagnetic field propagates in space at the speed of light -300,000 km/s.

Rice. 6. Radio

2. Magnetotherapy

In the frequency spectrum different places occupied by radio waves, light, x-rays and others electromagnetic radiation. They are usually characterized by continuously interconnected electric and magnetic fields.

3. Synchrophasotrons

At present, a magnetic field is understood as a special form of matter consisting of charged particles. In modern physics, beams of charged particles are used to penetrate deep into atoms in order to study them. The force with which a magnetic field acts on a moving charged particle is called the Lorentz force.

4. Flow meters

The method is based on the application of Faraday's law for a conductor in a magnetic field: in the flow of an electrically conductive liquid moving in a magnetic field, an EMF is induced proportional to the flow velocity, which is converted by the electronic part into an electrical analog / digital signal.

5. DC generator

In the generator mode, the armature of the machine rotates under the influence of an external moment. Between the poles of the stator there is a constant magnetic flux penetrating the armature. The armature winding conductors move in a magnetic field and, therefore, an EMF is induced in them, the direction of which can be determined by the rule " right hand". In this case, a positive potential arises on one brush relative to the second. If a load is connected to the generator terminals, then a current will flow in it.

6. Transformers

Transformers are widely used in the transmission of electrical energy over long distances, its distribution between receivers, as well as in various rectifying, amplifying, signaling and other devices.

The transformation of energy in the transformer is carried out by an alternating magnetic field. The transformer is a core of thin steel plates insulated from one another, on which two, and sometimes more windings (coils) of insulated wire are placed. The winding to which the source of AC electrical energy is connected is called the primary winding, the remaining windings are called secondary.

If three times more turns are wound in the secondary winding of the transformer than in the primary, then the magnetic field created in the core by the primary winding, crossing the turns of the secondary winding, will create three times more voltage in it.

By using a transformer with a reverse ratio of turns, you can just as easily and simply get a reduced voltage.

List of used literature

1. [Electronic resource]. Electromagnetic induction.

< https://ru.wikipedia.org/>

2. [Electronic resource]. Faraday. Discovery of electromagnetic induction.

< http://www.e-reading.club/chapter.php/26178/78/Karcev_-_Maksvell.html >

3. [Electronic resource]. Discovery of electromagnetic induction.

4. [Electronic resource]. Practical application of the phenomenon of electromagnetic induction.