Ohm's law. History and essence of scientific discovery

MOST IMPORTANT SCIENTIFIC DISCOVERIES
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Ohm's law. History and essence of scientific discovery

The most important scientific discoveries

Directory / The most important scientific discoveries

A conductor is simply a passive component of an electrical circuit. This opinion prevailed until the forties of the nineteenth century. So why waste time researching it?

Stefano Marianini (1790–1866) was one of the first scientists to address the issue of the conductivity of conductors. He came to his discovery by accident, studying the voltage of batteries. Stefano noticed that with an increase in the number of elements of the Voltaic column, the electromagnetic effect on the arrow does not increase noticeably. This made Marianini immediately think that each voltaic element was an obstacle to the passage of current. He conducted experiments with pairs of "active" and "inactive" (i.e., consisting of two copper plates separated by a wet gasket) and empirically found a relation in which the modern reader recognizes a special case of Ohm's law, when the resistance of the external circuit is not taken into attention, as it was in Marianini's experience.

Om recognized the merits of Marianini, although his works did not become a direct help in the work.

Georg Simon Ohm (1789-1854) was born in Erlangen, in the family of a hereditary locksmith. The role of the father in the upbringing of the boy was enormous, and, perhaps, he owes everything he achieved in life to his father. After leaving school, George entered the city gymnasium. The Erlangen Gymnasium was supervised by the university and was an educational institution corresponding to that time.

Having successfully graduated from the gymnasium, Georg in the spring of 1805 began to study mathematics, physics and philosophy at the Faculty of Philosophy of the University of Erlangen.

After studying for three semesters, Ohm accepted an invitation to take a position as a mathematics teacher in a private school in the Swiss town of Gottstadt. In 1809, Georg was asked to vacate his position and accept an invitation to teach mathematics in the city of Neustadt. There was no other choice, and by Christmas he had moved to a new place. But the dream of graduating from university does not leave Omagh. In 1811 he returned to Erlangen. Om's self-study was so fruitful that he was able to graduate from the university the same year, successfully defend his dissertation and receive a Ph.D. Immediately after graduating from the university, he was offered the position of Privatdozent of the Department of Mathematics of the same university.

Teaching work was quite consistent with the desires and abilities of Ohm. But, having worked for only three semesters, for material reasons that had haunted him almost all his life, he was forced to look for a better paid position.

By royal decision of December 16, 1812, Ohm was appointed teacher of mathematics and physics at the school in Bamberg. In February 1816 the real school in Bamberg was closed. A math teacher was offered to teach overcrowded classrooms at a local preparatory school for the same fee.

Having lost all hope of finding a suitable teaching job, the desperate Ph.D. unexpectedly receives an offer to take the place of a teacher of mathematics and physics in the Jesuit College of Cologne. He immediately leaves for the place of future work.

Here, in Cologne, he worked for nine years. It was here that he "transformed" from a mathematician into a physicist. The presence of free time contributed to the formation of Ohm as a research physicist. He enthusiastically gives himself to a new job, sitting for long hours in the workshop of the board and in the instrument store.

Ohm took up the study of electricity. He began his experimental studies by determining the relative values of the conductivity of various conductors. Applying a method that has now become classical, he connected in series between two points of the circuit thin conductors of various materials of the same diameter and changed their length so that a certain amount of current was obtained.

As V.V. Koshmanov, “Om knew about the appearance of the works of Barlow and Becquerel, which described the experimental search for the law of electrical circuits. He also knew about the results that these researchers came to. Although both Ohm, and Barlow, and Becquerel used a magnetic needle as a recording device , observed special care in connecting the circuit and the source of electric current was in principle the same design, but the results they obtained were different.The truth stubbornly eluded the researchers.

It was necessary, first of all, to eliminate the most significant source of errors, which, according to Ohm, was the galvanic battery.

Already in his first experiments, Ohm noticed that the magnetic effect of the current when the circuit is closed with an arbitrary wire decreases with time ...

This decrease practically did not stop over time, and it was clear that it was pointless to search for the law of electrical circuits in this state of affairs. It was necessary either to use a different type of electrical energy generator from those already available, or to create a new one, or to develop a circuit in which a change in the EMF would not affect the results of the experiment. Om went the first way."

After the publication of Ohm's first article, Poggendorf advised him to abandon the chemical elements and better use the copper-bismuth thermocouple, introduced shortly before by Seebeck. Ohm heeded this advice and repeated his experiments, assembling an installation with a thermoelectric battery, in the external circuit of which eight copper wires of the same diameter, but of different lengths, were connected in series. He measured the current strength with the help of a kind of torsion balance, formed by a magnetic needle suspended on a metal thread. When the current parallel to the needle deflected it, Om twisted the thread on which it was suspended until the needle was in its usual position; the current strength was considered proportional to the angle at which the thread was twisted.

Ohm came to the conclusion that the results of experiments carried out with eight different wires can be expressed by the equation - the quotient of аdivided by х + вWhere х means the intensity of the magnetic action of the conductor, the length of which is equal to х, а и в - constants depending, respectively, on the exciting force and on the resistance of the remaining parts of the circuit.

The conditions of the experiment changed: resistances and thermoelectric pairs were replaced, but the results still boiled down to the above formula, which very easily goes into the one we know if we replace х current strength, а - electromotive force and в + х - the total resistance of the circuit.

Ohm also experiments with four brass wires - the result is the same. “An important conclusion follows from this,” writes Koshmanov, “that the formula found by Ohm, which relates the physical quantities characterizing the process of current flow in a conductor, is valid not only for conductors made of copper. Using this formula, you can calculate electrical circuits regardless of the material of the conductors used in this ...

... In addition, Ohm found that the constant β does not depend on either the exciting force or the length of the included wire. This fact gives grounds to assert that the value of characterizes the unchanging part of the chain. And since addition in the denominator of the resulting formula is possible only for quantities of the same names, then, therefore, the constant in, concludes Ohm, should characterize the conductivity of the unchanging part of the circuit.

In subsequent experiments, Ohm studied the effect of conductor temperature on their resistance. He brought the investigated conductors into the flame, placed them in water with crushed ice, and made sure that the electrical conductivity of the conductors decreases with increasing temperature and increases with decreasing it.

Having received his famous formula, Ohm uses it to study the action of the Schweigger multiplier on the deflection of the arrow and to study the current that passes in the external circuit of the battery of cells, depending on how they are connected - in series or in parallel. Thus, he explains what determines the external current of the battery, a matter that was rather obscure for the first researchers.

Ohm's famous article "The definition of the law according to which metals conduct contact electricity, together with a sketch of the theory of the voltaic apparatus and the Schweigger multiplier", published in 1826 in the Journal of Physics and Chemistry, appears.

The appearance of an article containing the results of experimental research in the field of electrical phenomena did not impress scientists. None of them could even imagine that the law of electrical circuits established by Ohm is the basis for all electrical calculations of the future.

In 1827, in Berlin, he published his main work, The Galvanic Circuit Designed Mathematically.

Ohm was inspired in his research by Jean-Baptiste Fourier's (1822–1768) Analytical Theory of Heat (1830). The scientist realized that the mechanism of "heat flow", which Fourier speaks of, can be likened to an electric current in a conductor. And just as in Fourier theory the heat flow between two bodies or between two points of the same body is explained by the difference in temperature, so Ohm explains the difference in "electroscopic forces" at two points of the conductor, the occurrence of an electric current between them.

Ohm introduces the concepts and precise definitions of the electromotive force, or "electroscopic force", in the words of the scientist himself, electrical conductivity and current strength. Having expressed the law he derived in the differential form given by modern authors, Ohm also writes it down in finite values for special cases of specific electrical circuits, of which the thermoelectric circuit is especially important. Based on this, he formulates the known laws of change in electrical voltage along the circuit.

But Ohm's theoretical research also went unnoticed. Ohm's theoretical work shared the fate of the work containing his experimental research. The scientific world was still waiting. Only in 1841 was Ohm's work translated into English, in 1847 into Italian, and in 1860 into French.

Russian physicists were the first to recognize Ohm's law among foreign scientists. Lenz and Jacobi. They also helped its international recognition. With the participation of Russian physicists, on May 5, 1842, the Royal Society of London awarded Ohm with a gold medal and elected Ohm as its member. Ohm became only the second German scientist to receive such an honor.

His American colleague spoke very emotionally about the merits of the German scientist J Henry "When I first read Ohm's theory," he wrote, "it seemed to me like lightning, suddenly illuminating a room plunged into darkness."

Professor of physics at the University of Munich E. Lommel accurately spoke about the significance of Ohm's research at the opening of a monument to the scientist in 1895. “Ohm's discovery was a bright torch that illuminated the area of electricity that had been shrouded in darkness before him. Ohm showed the only correct path through the impenetrable forest of incomprehensible facts. The remarkable progress in the development of electrical engineering, which we have observed with astonishment in recent decades, could only be achieved on the basis of Ohm's discovery. secret and passed it into the hands of his contemporaries.

Author: Samin D.K.

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