FARADEUS. DISCOVERY OF ELECTROMAGNETIC INDUCTION
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 (say, into 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.
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 is of 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!
Faraday was at a loss: first, why does the needle behave so strangely? Secondly, are the bursts he noticed related to the phenomenon he was looking for?
It was then that Ampère'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, a new series of 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 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.
Faraday knows in advance how it will be. The experience works out brilliantly.
“I took a cylindrical magnetic bar (3/4" in diameter and 8 1/4" long) and inserted one end of it into a coil 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."
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, with the help of sliding contacts (one on the axis, the other on the periphery of the disk), it was possible to remove electrical voltage. It was the first electric generator created by human hands.
After the "electromagnetic epic" Faraday was forced to stop his work for several years. scientific work- his nervous system was so exhausted ...
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 (for example, he made accurate measurements of the speed of sound in water on Lake Geneva). 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 the price for their prejudice.
Faraday, too, was at first embarrassed by the transience of the effect, but he trusted facts more than theories, and eventually came to the law electromagnetic induction. This law then seemed to physicists flawed, ugly, strange, devoid of internal logic.
Why is the current excited only during the movement of the magnet or the change in current in the winding?
Nobody understood this. Even Faraday himself. Seventeen years later, the twenty-six-year-old army surgeon of the provincial garrison in Potsdam, Hermann Helmholtz, understood this. In the classic article “On the Conservation of Force,” he, formulating his law of conservation of energy, proved for the first time that electromagnetic induction must exist in this “ugly” form.
Maxwell's older friend, William Thomson, also came to this independently. He also obtained Faraday's electromagnetic induction from Ampère's law, taking into account the law of conservation of energy.
So the "fleeting" electromagnetic induction acquired the rights of citizenship and was recognized by physicists.
But it did not fit into the concepts and analogies of Maxwell's article "On Faraday lines of force". And this was a serious shortcoming of the article. In practice, its significance was reduced to illustrating the fact that the theories of short-range and long-range interactions represent different mathematical descriptions of the same experimental data, that Faraday's lines of force do not contradict common sense. And it's all. Everything, although it was already a lot.
From Maxwell's book author Kartsev Vladimir PetrovichTO THE ELECTROMAGNETIC THEORY OF LIGHT The article "On physical lines of force" was published in parts. And the third part of it, like both previous ones, contained new ideas of extraordinary value. Maxwell wrote: “It is necessary to assume that the substance of the cells has an elasticity of form,
From the book Werner von Siemens - biography author Weiher Siegfried vontransatlantic cable. Cable ship "Faraday" The obvious success of the Indo-European line, both technically and financially, should have inspired its creators to further undertakings. The opportunity to start a new business presented itself, and the inspiration turned out to be
From the book Fermat's Great Theorem author Singh SimonAppendix 10. An example of a proof by induction In mathematics, it is important to have exact formulas that allow you to calculate the sum of various sequences of numbers. In this case, we want to derive a formula that gives the sum of the first n natural numbers. For example, "sum" is just
From Faraday's book author Radovsky Moses Izrailevich From the book by Robert Williams Wood. Modern Physics Lab Wizard author Seabrook William From the book Rustle of a Grenade author Prishchepenko Alexander BorisovichCHAPTER ELEVEN Wood stretches his vacation year into three, stands where Faraday once stood, and crosses the length and breadth of our planet The average university professor is happy if he manages to get a free year every seven years. But Wood is not
From the book of Kurchatov author Astashenkov Petr Timofeevich From the book Journey Around the World the author Forster GeorgHere it is, the discovery! Die Hard Academician Ioffe and his collaborators have long been interested in the unusual behavior of Rochelle salt crystals (double potassium salt of tartaric acid) in an electric field. This salt has been little studied so far, and there have been only
From the book Zodiac author Graysmith Robert From the book 50 geniuses who changed the world author Ochkurova Oksana Yurievna1 DAVID FARADAY AND BETTY LOU JENSEN Friday, December 20, 1968 David Faraday drove slowly through the gentle hills of Vallejo, not turning special attention to the Golden Gate Bridge, to the yachts and gliders that flickered in San Pablo Bay, to the clear silhouettes of harbor cranes and
From the book Uncooled Memory [collection] author Druyan Boris GrigorievichMichael Faraday (born in 1791 - died in 1867) An outstanding English scientist, physicist and chemist, the founder of the theory of the electromagnetic field, who discovered electromagnetic induction - a phenomenon that formed the basis of electrical engineering, as well as the laws of electrolysis, called him
From Francis Bacon author Subbotin Alexander LeonidovichOpening One of the cloudy autumn days of 1965 in the editorial fiction A young man appeared at Lenizdat with a skinny clerical folder in his hand. One could guess with absolute certainty that it contained poetry. He was clearly embarrassed and, not knowing to whom
From the book Dancing in Auschwitz author Glaser Paul From the book Great Chemists. In 2 volumes. T.I. author Manolov KaloyanDiscovery One of my colleagues is from Austria. We are friends, and one evening while talking, he notices that the surname Glaser was very common in pre-war Vienna. My father once told me, I remember, that our distant ancestors lived in the German-speaking part
From Nietzsche's book. For those who want to do everything. Aphorisms, metaphors, quotes author Sirota E. L.MICHAEL FARADAY (1791-1867) The air in the bookbinding shop was filled with the smell of wood glue. Sitting among a pile of books, the workers chatted merrily and diligently sewed printed sheets together. Michael was gluing a thick volume of the Encyclopædia Britannica. He wanted to read it
From the author's bookDiscovery of the South In the autumn of 1881, Nietzsche fell under the spell of Georges Bizet's work - he listened to his "Carmen" in Genoa about twenty times! Georges Bizet (1838-1875) - the famous French romantic composer Spring 1882 - a new journey: from Genoa by ship to Messina, about which a little
The phenomenon of electromagnetic induction was discovered by Mile Faraday in 1831. Even 10 years earlier, Faraday was thinking about a way to turn magnetism into electricity. He believed that the magnetic field and electric field must be connected somehow.
Discovery of electromagnetic induction
For example, using electric field You can magnetize an iron object. Probably, it should be possible with the help of a magnet to get electricity.
First, Faraday discovered the phenomenon of electromagnetic induction in conductors that are stationary relative to each other. When a current appeared in one of them, a current was also induced in the other coil. Moreover, in the future it disappeared, and appeared again only when the power to one coil was turned off.
After some time, Faraday proved in experiments that when a coil without current is moved in a circuit relative to another, at the ends of which voltage is applied, an electric current will also appear in the first coil.
The next experiment was the introduction of a magnet into the coil, and at the same time, a current also appeared in it. These experiments are shown in the following figures.
Faraday formulated the main reason for the appearance of current in a closed circuit. In a closed conducting circuit, current arises when the number of magnetic induction lines that permeate this circuit changes.
The more this change is, the stronger it will be. induction current. It does not matter how we achieve a change in the number of lines of magnetic induction. For example, this can be done by moving the contour in a non-uniform magnetic field, as happened in the experiment with a magnet or the movement of a coil. And we can, for example, change the current strength in the coil adjacent to the circuit, while the magnetic field created by this coil will change.
The wording of the law
Let's sum up summary. The phenomenon of electromagnetic induction is the phenomenon of the occurrence of current in a closed circuit, with a change magnetic field in which this circuit is located.
For a more precise formulation of the law of electromagnetic induction, it is necessary to introduce a value that would characterize the magnetic field - the flux of the magnetic induction vector.
magnetic flux
The magnetic induction vector is denoted by the letter B. It will characterize the magnetic field at any point in space. Now consider a closed contour bounding the surface with area S. Let us place it in a uniform magnetic field.
There will be some angle a between the normal vector to the surface and the magnetic induction vector. The magnetic flux Ф through a surface with an area S is called physical quantity, equal to the product of the modulus of the magnetic induction vector and the surface area and the cosine of the angle between the magnetic induction vector and the normal to the contour.
F \u003d B * S * cos (a).
The product B*cos(a) is the projection of the vector B onto the normal n. Therefore, the form for magnetic flux can be rewritten like this:
The unit of magnetic flux is the weber. Denoted 1 Wb. A magnetic flux of 1 Wb is created by a magnetic field with an induction of 1 T through a surface with an area of 1 m ^ 2, which is located perpendicular to the magnetic induction vector.
Electromagnetic induction- this is a phenomenon that consists in the occurrence of an electric current in a closed conductor as a result of a change in the magnetic field in which it is located. This phenomenon was discovered by the English physicist M. Faraday in 1831. Its essence can be explained by several simple experiments.
Described in Faraday's experiments receiving principle alternating current used in induction generators generating electrical energy in thermal or hydroelectric power plants. The resistance to rotation of the generator rotor, which occurs when the induction current interacts with the magnetic field, is overcome by the operation of a steam or hydraulic turbine that rotates the rotor. Such generators convert mechanical energy into electrical energy .
Eddy currents, or Foucault currents
If a massive conductor is placed in an alternating magnetic field, then in this conductor, due to the phenomenon of electromagnetic induction, eddy induction currents arise, called Foucault currents.
Eddy currents also arise when a massive conductor moves in a constant, but inhomogeneous magnetic field in space. Foucault currents have such a direction that the force acting on them in a magnetic field slows down the movement of the conductor. A pendulum in the form of a solid metal plate made of non-magnetic material, which oscillates between the poles of an electromagnet, stops abruptly when the magnetic field is turned on.
In many cases, the heating caused by Foucault currents turns out to be harmful and has to be dealt with. The cores of transformers, the rotors of electric motors are made from separate iron plates separated by layers of an insulator that prevents the development of large induction currents, and the plates themselves are made from alloys with high resistivity.
Electromagnetic field
The electric field created by stationary charges is static and acts on the charges. A direct current causes the appearance of a magnetic field constant in time, acting on moving charges and currents. Electric and magnetic fields exist in this case independently of each other.
Phenomenon electromagnetic induction demonstrates the interaction of these fields, observed in substances in which there are free charges, i.e., in conductors. An alternating magnetic field creates an alternating electric field, which, acting on free charges, creates an electric current. This current, being alternating, in turn generates an alternating magnetic field, which creates an electric field in the same conductor, etc.
The combination of alternating electric and alternating magnetic fields that generate each other is called electromagnetic field . It can also exist in a medium where there are no free charges, and propagates in space in the form electromagnetic wave.
classical electrodynamics- one of the highest achievements of the human mind. She had a huge impact on the subsequent development of human civilization, predicting the existence of electromagnetic waves. This later led to the creation of radio, television, telecommunications systems, satellite navigation, as well as computers, industrial and domestic robots and other attributes of modern life.
cornerstone Maxwell's theories was the assertion that only an alternating electric field can serve as a source of a magnetic field, just as an alternating magnetic field serves as a source of an electric field that creates an induction current in a conductor. The presence of a conductor in this case is not necessary - an electric field also arises in empty space. The lines of an alternating electric field, similarly to the lines of a magnetic field, are closed. The electric and magnetic fields of an electromagnetic wave are equal.
Electromagnetic induction in diagrams and tables
The history of the discovery of electromagnetic induction. The discoveries of Hans Christian Oersted and André Marie Ampère showed that electricity has a magnetic force. The influence of magnetic phenomena on electrical phenomena was discovered by Michael Faraday. Hans Christian Oersted André Marie Ampère
Michael Faraday () "Turn magnetism into electricity," he wrote in his diary in 1822. English physicist, founder of the theory of the electromagnetic field, foreign honorary member of the St. Petersburg Academy of Sciences (1830).
Description of Michael Faraday's experiments wooden block wound two copper wires. One of the wires was connected to a galvanometer, the other to a strong battery. When the circuit was closed, a sudden but extremely weak action was observed on the galvanometer, and the same action was noticed when the current was stopped. With the continuous passage of current through one of the spirals, it was not possible to detect deviations of the galvanometer needle
Description of the experiments of Michael Faraday Another experiment consisted in registering current surges at the ends of the coil, inside which permanent magnet. Faraday called such bursts "waves of electricity"
EMF of induction The EMF of induction, which causes bursts of current ("waves of electricity"), does not depend on the magnitude of the magnetic flux, but on the rate of its change.
1. Determine the direction of the lines of induction of the external field B (they leave N and enter S). 2. Determine whether the magnetic flux through the circuit increases or decreases (if the magnet is pushed into the ring, then Ф> 0, if it is pulled out, then Ф 0, if it is pulled out, then Ф 0, if it is pulled out, then Ф 0, if it is pulled out, then Ф 0 , if extended, then Ф 
3. Determine the direction of the induction lines of the magnetic field B created by the inductive current (if F>0, then the lines B and B are directed in opposite directions; if F 0, then the lines B and B are directed in opposite directions; if F 0, then the lines B and B are directed in opposite directions; if Ф 0, then lines B and B are directed in opposite directions; if Ф 0, then lines B and B are directed in opposite directions; if Ф 
Questions Formulate the law of electromagnetic induction. Who is the founder of this law? What is induced current and how to determine its direction? What does it depend on EMF value induction? The principle of operation of which electrical devices is based on the law of electromagnetic induction?
Before answering the question of who discovered the phenomenon of electromagnetic induction, let us consider what the situation was at that time in scientific world in the relevant field of knowledge. Discovery in 1820 by H.K. Oersted's magnetic field around a wire with current caused a wide resonance in scientific circles. There have been many experiments in the field of electricity. The idea of electromagnetic rotation around a current-carrying conductor was proposed by Wollaston. M. Faraday came to this idea himself and created the first model of an electric motor in 1821. The scientist ensured the action of current on one pole of the magnet, using a mercury contact, he realized the continuous rotation of the magnet around a current-carrying conductor. It was then that M. Faraday formulated the following task in his diary: to turn magnetism into electricity. It took almost ten years to solve this problem. Only in November 1831 did M. Faraday begin to systematically publish the results of his research on this subject. Faraday's classic experiments to detect the phenomenon of electromagnetic induction were:
First experience:
A galvanometer is taken, which is closed to a solenoid. A permanent magnet is pushed into or out of the solenoid. When the magnet moves, the deflection of the galvanometer needle is observed, which indicates the appearance of an induction current. In this case, the higher the speed of the magnet relative to the coil, the greater the deviation of the arrow. If the poles of the magnet are reversed, the direction of deviation of the galvanometer needle will change. It must be said that in a variation of this experiment, the magnet can be made immobile and the solenoid can be moved relative to the magnet.
Second experience:
There are two coils. One is inserted into the other. The ends of one coil are connected to a galvanometer. An electric current is passed through the other coil. The galvanometer needle deviates at the moments of switching on (off) the current, its change (increase or decrease) or when the coils move relative to each other. In this case, the direction of deviation of the galvanometer needle is opposite when the current is turned on and off (decrease - increase).
After summarizing his experiments, M. Faraday concluded that the induction current always appears when the magnetic induction flux coupled to the circuit changes. In addition, it was found that the magnitude of the induction current does not depend on the way in which the change in the magnetic flux occurs, but is determined by the rate of its change. In his experiments, M. Faraday showed that the angle of deviation of the galvanometer needle depends on the speed of the magnet (or the rate of change in the current strength, or the speed of the coils). And so, the results of Faraday's experiments in this area can be reduced to the following:
The electromotive force of induction appears when the magnetic flux changes (see details on the page "").
The connection established by M. Faraday between electricity and magnetism Maxwell wrote down in mathematical form. At present, we know this entry as the law of electromagnetic induction (Faraday's law) (p. " ").