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MOST IMPORTANT SCIENTIFIC DISCOVERIES
Electromagnetic induction. History and essence of scientific discovery
Directory / The most important scientific discoveries After discoveries Oersted и Ampere it became clear that electricity has a magnetic force. Now it was necessary to confirm the influence of magnetic phenomena on electrical ones. This problem was brilliantly solved by 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 of 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. Faraday began to make physical and chemical experiments 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 physical 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 his predecessors and combining several of his 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. The following 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. 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. As usual, Faraday began a series of experiments that were supposed to clarify the essence of the matter. 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. He immediately noticed that the galvanometer, remaining perfectly still during the entire passage of the current, comes into oscillation at the very closing of the circuit and at its opening. 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. These secondary instantaneous currents, caused by the influence of primary ones, were called inductive by Faraday, and this name has been preserved for them until now. 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 (switch), 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. Thus, a new source of electrical energy was found, in addition to the previously known ones (friction and chemical processes), - induction, and a new type of this energy - induction electricity. 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 became a magnet when an insulated wire was wound around it and a galvanic current passed through it, and that the magnetic properties of this iron ceased as soon as the current ceased. 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. 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; that this explanation was intensively sought by such eminent scientists of the time as Arago himself, Ampère, Poisson, Babaj and Herschel. 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 inserting 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, in 1831 gave the name "lines of magnetic force" to magnetic curves, 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. Further works of Faraday in the mentioned direction acquired, from the modern 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. A number of studies in the field of electrical induction Faraday ended 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. Russian physicist Emil Khristoforovich Lenz (1804–1861) gave a rule for determining the direction of an 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 a coil approaches a 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. Why is there an induced current? A deep explanation of the phenomenon of electromagnetic induction was given by an English physicist James Clerk Maxwell - the creator of the 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 an electric field. The essence of the phenomenon of electromagnetic induction is that an alternating magnetic field always generates an electric field with closed lines of force in the surrounding space. 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 of the XNUMXth century - the work of millions of electric motors and electric current generators around the world is based on this phenomenon ... Author: Samin D.K.
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