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MOST IMPORTANT SCIENTIFIC DISCOVERIES
Electrodynamics. History and essence of scientific discovery
Directory / The most important scientific discoveries Right after Oersted's discoveries it seemed quite natural to physicists to explain it by the fact that when an electric current passes through a conductor, the latter becomes a magnet. This explanation was accepted by Arago, it was also accepted by Biot. The latter in 1820 made the following assumption. When a rectilinear current acts on a magnetic molecule, the nature of this action is the same as for a magnetized needle placed on the periphery of a conductor in a certain direction, constant with respect to the direction of the voltaic current. Biot and other physicists who shared his opinion explained the electrodynamic action by the interaction of elementary magnets that arise under the action of current in each conductor: each conductor through which the current passes turns into a magnetic tube. He offered a completely different explanation. Ampere... But first, a few words about his biography. André-Marie Ampère (1775-1836) was born on the small estate of Polemier, bought by his father in the vicinity of Lyon. Andre's exceptional abilities manifested themselves at an early age. He never went to school, but he learned reading and arithmetic very quickly. The boy read everything in a row that he found in his father's library. Already at the age of 14, he read all twenty-eight volumes of the French Encyclopedia. Andre showed particular interest in the physical and mathematical sciences. But just in this area, his father's library was clearly not enough, and Andre began to visit the library of Lyon College to read the works of great mathematicians. At the age of 13, Ampère presented his first work in mathematics to the Lyon Academy. In 1789 the Great French bourgeois revolution began. Ampere's father was executed. He was left without funds. Andre had to think about his livelihood, and he decided to move to Lyon, give private lessons in mathematics until he could get a full-time teacher in any educational institution. The cost of living has risen steadily. Despite all the efforts and savings, the funds earned by private lessons were not enough. Finally, in 1802, Ampère was invited to teach physics and chemistry at the Central School of the ancient provincial town of Burkan Bres, 60 kilometers from Lyon. From that moment began his regular teaching activity, which continued throughout his life. April 4, 1803 Ampère was appointed teacher of mathematics at the Lyon Lyon. At the end of 1804, Ampère left Lyon and moved to Paris, where he received a teaching position at the famous Polytechnic School. In 1807, Ampère was appointed professor at the Polytechnic School. In 1808, the scientist received the post of chief inspector of universities. Between 1809 and 1814 Ampère published several valuable papers on the theory of series. The heyday of Ampère's scientific activity falls on the years 1814-1824 and is associated mainly with the Academy of Sciences, to which he was elected a member on November 28, 1814 for his merits in the field of mathematics. Almost until 1820, the main interests of the scientist focused on the problems of mathematics, mechanics and chemistry. His achievements in the field of chemistry should include the discovery, regardless of Avogadro, the law of equality of molar volumes of various gases. It should rightfully be called the Avogadro-Ampère law. The scientist also made the first attempt to classify chemical elements based on a comparison of their properties. As for mathematics, it was in this area that he achieved results, which gave grounds to nominate him as a candidate for the Academy in the mathematical department. Ampere always considered mathematics as a powerful tool for solving various applied problems of physics and technology. At that time, he was very little involved in physics issues: only two works of this period are known, devoted to optics and the molecular-kinetic theory of gases. In 1820, the Danish physicist G.-H. Oersted discovered that a magnetic needle deviates near a current-carrying conductor. Thus, a remarkable property of electric current was discovered - to create a magnetic field. Ampère studied this phenomenon in detail. A new view of the nature of magnetic phenomena arose from him as a result of a whole series of experiments. Already at the end of the first week of hard work, he made a discovery of no less importance than Oersted - he discovered the interaction of currents. On September 18, 1820, he informed the Paris Academy of Sciences about his discovery of ponderomotive interactions of currents, which he called electrodynamic. More precisely, in this first report of his, Ampère called these actions "voltaic attraction and repulsion", but then he began to call them "attraction and repulsion of electric currents." In 1822 he coined the term "electrodynamic". Then he demonstrated his first experiments and concluded them with the following words: "In this regard, I reduced all magnetic phenomena to purely electrical effects." At a meeting on September 25, he developed these ideas further, demonstrating experiments in which spirals flowed around by current (solenoids) interacted with each other like magnets. Ampere's explanation is his outstanding contribution to science: it is not a conductor through which a current flows that becomes a magnet, but, on the contrary, a magnet is a collection of currents. Indeed, says Ampere, if we assume that there is a set of circular currents in the magnet, flowing in planes exactly perpendicular to its axis, in the same direction, then the current running parallel to the axis of the magnet will turn out to be directed at an angle to these circular currents. currents, which will cause an electrodynamic interaction that tends to make all currents parallel and directed in the same direction. If the straight conductor is fixed and the magnet is movable, then the magnet is deflected; if the magnet is fixed and the conductor is movable, then the conductor moves. As Mario Gliozzi writes in his book: “He (Amp. - Approx. Aut.) thought that if a magnet is understood as a system of circular parallel currents directed in one direction, then a spiral of metal wire through which the current passes must behave like a magnet, that is, it must take a certain position under the influence of the Earth's magnetic field and have two poles.Experiment confirmed the assumptions regarding the behavior of such a spiral under the action of a magnet, but the results of the experiment relating to the behavior of the spiral under the influence of the Earth's magnetic field were not entirely clear. Then Ampère decided to take a single turn of a current-carrying conductor to clarify this question; it turned out that the turn behaves exactly like a magnetic sheet. Thus, an incomprehensible phenomenon was discovered: a single coil behaves like a magnetic plate, and a spiral, which Ampère considered to be exactly equivalent to a system of magnetic plates, did not behave quite like a magnet. Trying to figure out what was the matter, Ampère was surprised to find that in electrodynamic phenomena a spiral conductor behaves exactly like a straight conductor with the same ends. From this, Ampère concluded that with regard to electrodynamic and electromagnetic actions, current elements can be added and expanded according to the parallelogram rule. Therefore, the current element can be decomposed into two components, of which one is directed parallel to the axis, and the other is perpendicular. If we sum up the results of the action of different elements of the spiral, then the resulting one will be equivalent to a rectilinear current flowing along the axis, and a system of circular currents located perpendicular to the axis and directed in one direction. Therefore, in order for the spiral through which the current passes to behave exactly like a magnet, it is necessary to compensate for the action of the rectilinear current. As you know, Ampere achieved this very simply by bending the ends of the conductor along the axis. But still there was a difference between the spiral through which the current passes and the magnet: the poles of the spiral were only at the ends, while the poles of the magnet were at internal points. To eliminate this last difference, Ampère abandoned his original hypothesis about currents directly perpendicular to the axis of the magnet, and assumed that they are located in planes at different angles to the axis. Ampere's new ideas were not understood by all scientists. Some of his eminent colleagues did not agree with them either. Contemporaries said that after the first report of Ampere on the interaction of conductors with current, the following curious episode occurred. “What, in fact, is new in what you told us?” one of his opponents asked Ampere. “It goes without saying that if two currents have an effect on a magnetic needle, then they also have an effect on each other.” Ampère did not immediately find an answer to this objection. But then Arago came to his aid. He took out two keys from his pocket and said: “Each of them also has an effect on the arrow, however, they do not act on each other in any way, and therefore your conclusion is erroneous. Ampère discovered, in essence, a new phenomenon, of much greater significance, than the discovery of Professor Oersted, respected by me." Despite the attacks of his scientific opponents, Ampère continued his experiments. He decided to find the law of interaction of currents in the form of a strict mathematical formula and found this law, which now bears his name. So step by step in the works of Ampère a new science grew up - electrodynamics, based on experiments and mathematical theory. All the basic ideas of this science, in the expression Maxwell, in fact, "came out of the head of this Newton of electricity" in two weeks. From 1820 to 1826, Ampère published a number of theoretical and experimental works on electrodynamics, and at almost every meeting of the Physics Department of the Academy he delivered a report on this topic. In 1826, his final classic work, The Theory of Electrodynamic Phenomena Derived Exclusively from Experience, was published. The effect of the interaction of wires with current and magnetic fields is now used in electric motors, in electrical relays and in many electrical measuring instruments. Author: Samin D.K.
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