Crisis of resistance. Biography of Georg Simon Ohm Philosophy of studies

18.04.2024

Georg Simon Ohm was born into a Protestant family, Johann Wolfgang Ohm and Maria Elisabeth Beck. His father was a plumber, and his mother was the daughter of a tailor. My parents did not have an academic education, but this did not stop my father from educating himself. Johann, based on the knowledge he acquired, independently began to educate his own children. Georg had a younger brother, Martin, who later became a famous mathematician, and a sister, Elizabeth Barbara. George, together with his brother Martin, through their efforts achieved such heights in mathematics, physics, chemistry and philosophy that there was no longer any need for an academic education for boys. However, at the age of 11, Georg entered the Erlangen Gymnasium, where he would study until the age of fifteen. But the boy did not like this stage of training, consisting, in his own words, only in the development of mechanical memory and interpretation of texts. The Ohm brothers' level of education was so high that Karl Christian von Langsdorff, a professor at the University of Erlangen, compared the boys to the Bernoulli family.

In 1805, Georg Ohm entered the University of Erlagen. Instead of focusing on his studies, he devotes all his time to extracurricular activities. Johann, who noticed that his son was wasting precious years and missing out on the opportunity to receive a decent education, sent his son to Switzerland in 1806. There, in the town of Gottstadt in the Nidau district, Georg becomes a school mathematics teacher. In 1809, Karl Christian von Langsdorff left his post at the University of Erlangen and moved to the University of Heidelberg. Ohm also wanted to follow him, but he, having dissuaded the future scientist, advised him to instead take up the study of the works of Euler, Laplace and Lacroix. In March 1809, Ohm left his teaching post and moved to Neuchâtel, where he gave private lessons. He devotes his free time to independent study of mathematics. This continues for two whole years, until April 1811, after which Ohm returns to the University of Erlangen.

Teaching activities

Georg Ohm achieved such heights in his private teaching practice that he was able to prepare for his doctorate on his own. On October 25, 1811, at the University of Erlangen, Ohm received the scientific degree of Doctor of Philosophy. Immediately after this, he became a lecturer at the university department of mathematics. But he will stay there for only three months, and then, realizing the lack of any prospects, he will leave the university. Om lived in extreme poverty, and the meager salary of the lecturer could not improve his plight. In 1813, responding to the offer of the Bavarian authorities, Ohm became a teacher of mathematics and physics in Bamberg. But, being dissatisfied with this position, George, in order to somehow prove himself, begins to write a textbook on the initial course of geometry. In 1816, the school closed, and Ohm moved to another school overcrowded with students, all in the same Bamberg.

The following year, in September 1817, Ohm was offered the post of teacher of mathematics and physics at the Jesuit Gymnasium in Cologne. This chance could not be missed, since this gymnasium was not only better than all the educational institutions in which he taught before, but also had a well-equipped laboratory. Throughout his teaching career, Ohm never for a moment abandoned his self-education, studying the works of learned French mathematicians: Lagrange, Legendre, Laplace, Biot and Poisson. Later, Ohm would become acquainted with the works of Fourier and Fresnel. And at the same time, having learned about Oersted’s theoretical substantiation of the phenomenon of electromagnetism in 1820, George began to conduct his own experiments in the school physics laboratory. He does this solely to raise his own level of knowledge. Om also realizes that if he wants to get a job that will be truly interesting, he will have to work on research materials. After all, only by relying on something could he show himself to the world and achieve what he wanted.

Ohm's research

In 1825, Ohm presented an article to the scientific community in which he established that the electromagnetic force in a conductor decreases as the length of this conductor increases. The article is based solely on evidence obtained experimentally during our own experiments. Two more articles will appear this year. In one of them, the scientist gives a mathematical justification for conductivity in an electrical circuit, based on the Fourier theory of thermal conductivity. The second article was of extreme importance because in it Ohm gave an explanation of the results of experiments carried out by other scientists with galvanic current. This very article became the precursor to what today we call “Ohm’s law,” published the following year. In 1827, Ohm published his famous work “Galvanic Circuits, Mathematical Justification,” in which he gives a detailed explanation of the theory of electrical circuits. The book is also valuable because, instead of proceeding directly to the object of study, Ohm first provides mathematical confirmation of the theory, necessary for further understanding of the subject. This became a very important point, since even the most outstanding German physicists needed such an introduction, because this book was that rare case in those days when the approach to physics was directly physical, and not mathematical. According to Ohm's theory, interactions in an electrical circuit occur between “equally charged particles.” And finally, this work clearly illustrated the differences between Ohm’s scientific approach and the works of Fourier and Navier.

Later years

In 1826, the Cologne Jesuit Gymnasium granted Ohm leave with half his salary to continue his scientific research, but in September 1827, the scientist was forced to resume his teaching duties. Throughout the year he spent in Berlin, he sincerely believed that his scientific publication would help him get a worthy place at some famous university. However, when this did not happen, he reluctantly returned to his previous place of work. But the worst part of the whole story was that, despite the importance of his work, the scientific world received it more than lukewarmly. Insulted, Om decides to move to Berlin. And in March 1828, he officially left his post at the Cologne Jesuit Gymnasium and took a temporary job as a mathematics teacher in various schools in Berlin. In 1833, the scientist accepted an offer to take the post of professor in Nuremberg. But even after receiving the coveted position, Om remains dissatisfied. The scientist's persistent and hard work was finally rewarded in 1842, when he received the Copley Medal of the British Royal Society. The very next year he was elected a foreign member of the society. In 1845 Ohm became a full member of the Bavarian Academy. Four years later, he holds the position of curator of the physics museum at the Bavarian Academy in Munich and lectures at the University of Munich. Only in 1852 did Ohm receive the position for which he had strived all his life: he was appointed head of the department of physics at the University of Munich.

Death and legacy

George Ohm's heart stopped in Munich in 1854. He was buried in the Old South Cemetery of Munich. Little is known about the causes of his death. The name of this scientist was included in the terminology of electricity in the name “Ohm’s law.” In addition, the unit of resistance in the International System of Units (SI), denoted by the Greek letter “Ω,” bears his name.

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Essay

Ohm's law. History of discovery. Different types of Ohm's law.

1. General view of Ohm's law.

2. The history of the discovery of Ohm’s law, a brief biography of the scientist.

3. Types of Ohm's laws.

Ohm's law establishes the relationship between current strength I in the conductor and potential difference (voltage) U between two fixed points (sections) of this conductor:

(1) Proportionality factor R, depending on the geometric and electrical properties of the conductor and on temperature, is called ohmic resistance or simply the resistance of a given section of the conductor. Ohm's law was discovered in 1826. physicist G. Ohm.

Georg Simon Ohm was born on March 16, 1787 in Erlangen, in the family of a hereditary mechanic. After graduating from school, Georg entered the city gymnasium. The Erlangen Gymnasium was supervised by the university. Classes at the gymnasium were taught by four professors. Georg, having graduated from high school, in the spring of 1805 began studying mathematics, physics and philosophy at the Faculty of Philosophy of the University of Erlangen.

After studying for three semesters, he accepted an invitation to take the place of a mathematics teacher in a private school in the Swiss town of Gottstadt.

In 1811 he returned to Erlangen, graduated from the university and received a Ph.D. Immediately after graduating from the university, he was offered the position of private assistant professor in the department of mathematics of the same university.

In 1812 Ohm was appointed teacher of mathematics and physics at a school in Bamberg. In 1817, he published his first printed work on teaching methods, “The most optimal option for teaching geometry in preparatory classes.” Om began researching electricity. Ohm based his electrical measuring instrument on the design of Coulomb's torsion balances. Ohm presented the results of his research in the form of an article entitled “Preliminary report on the law according to which metals conduct contact electricity.” The article was published in 1825 in the Journal of Physics and Chemistry, published by Schweigger. However, the expression found and published by Ohm turned out to be incorrect, which was one of the reasons for its long-term non-recognition. Having taken all precautions and eliminated all possible sources of error in advance, Om began new measurements.

His famous article “Definition of the law according to which metals conduct contact electricity, together with an outline of the theory of the voltaic apparatus and the Schweigger multiplier,” published in 1826 in the Journal of Physics and Chemistry, appears.

In May 1827, “Theoretical Studies of Electric Circuits” volume of 245 pages, which contained Ohm’s now theoretical reasoning on electric circuits. In this work, the scientist proposed to characterize the electrical properties of a conductor by its resistance and introduced this term into scientific use. Ohm found a simpler formula for the law of a section of an electrical circuit that does not contain EMF: “The magnitude of the current in a galvanic circuit is directly proportional to the sum of all voltages and inversely proportional to the sum of the reduced lengths. In this case, the total reduced length is defined as the sum of all individual reduced lengths for homogeneous sections having different conductivity and different cross-section."

In 1829, his article “An Experimental Study of the Operation of an Electromagnetic Multiplier” appeared, in which the foundations of the theory of electrical measuring instruments were laid. Here Ohm proposed a unit of resistance, for which he chose the resistance of a copper wire 1 foot long and with a cross section of 1 square line.

In 1830, Ohm's new study, “An Attempt to Create an Approximate Theory of Unipolar Conductivity,” appeared.

It was not until 1841 that Ohm's work was translated into English, in 1847 into Italian, and in 1860 into French.

On February 16, 1833, seven years after the publication of the article in which his discovery was published, Ohm was offered a position as professor of physics at the newly organized Polytechnic School of Nuremberg. The scientist begins research in the field of acoustics. Ohm formulated the results of his acoustic research in the form of a law, which later became known as Ohm’s acoustic law.

The Russian physicists Lenz and Jacobi were the first to recognize Ohm's law among foreign scientists. They also helped his international recognition. With the participation of Russian physicists, on May 5, 1842, the Royal Society of London awarded Ohm a gold medal and elected him a member.

In 1845 he was elected a full member of the Bavarian Academy of Sciences. In 1849, the scientist was invited to the University of Munich to the position of extraordinary professor. In the same year, he was appointed custodian of the state collection of physical and mathematical instruments, while simultaneously delivering lectures on physics and mathematics. In 1852, Ohm received the position of full professor. Ohm died on July 6, 1854. In 1881, at the electrical engineering congress in Paris, scientists unanimously approved the name of the unit of resistance - 1 Ohm.

In general, the relationship between I And U nonlinear, but in practice it is always possible to consider it linear in a certain voltage range and apply Ohm’s law; for metals and their alloys this range is practically unlimited.

Ohm's law in the form (1) is valid for sections of the circuit that do not contain sources of emf. In the presence of such sources (batteries, thermocouples, generators, etc.), Ohm’s law takes the form:

(2) - EMF of all sources included in the considered section of the circuit. For a closed circuit, Ohm's law takes the form: (3) - the total resistance of the circuit, equal to the sum of the external resistance r and internal resistance of the EMF source. A generalization of Ohm's law to the case of a branched chain is Kirchhoff's rule 2.

Ohm's law can be written in differential form, relating the current density at each point of the conductor j with full electric field strength. Potential. electric field strength E, created in conductors by microscopic charges (electrons, ions) of the conductors themselves, cannot support the stationary movement of free charges (current), since the work of this field on a closed path is zero. The current is maintained by non-electrostatic forces of various origins (inductive, chemical, thermal, etc.), which act in sources of emf and which can be represented as some equivalent non-potential field with intensity EST, called third party. The total field strength acting on charges inside the conductor is, in general, equal to E+ EST. Accordingly, Ohm's differential law has the form:

or , (4) is the resistivity of the conductor material, and is its electrical conductivity.

Ohm's law in complex form is also valid for sinusoidal quasi-stationary currents:

(5)

Where z - total complex resistance:

, r– active resistance, and x- circuit reactance. In the presence of inductance L and containers WITH in a circuit of quasi-stationary current frequency.

There are several types of Ohm's law.

regarding the storyline. according to the first part, as we know, our main pepper is a nomad (aka a nomad), who began to disentangle the whole mess. Along the way, in the plot, the jester and the Aztec stick their legs up, it’s sad, but what can we do, we still have a psycho prophet and the nomad himself in stock. let's move on. Without going too fast, let’s wedge in a plot from warhead here for a minute. the psycho himself, somewhere in Mukhopopinsk on the other side of the island, begins to recapture the container with the humanoid from the Koreans, while the latter are extremely dissatisfied. We conclude the warhead plot with the fact that the main narrow-eyed boy, the scoundrel, is defeated and the psycho returns with the box to the aircraft carrier. Let's go back to the first part. box on an aircraft carrier. All around there is a bustle of squids attacking all living things and trying in every possible way to return their brother - packed in a box, because the nomad infection has torn up the hive and now the seafood has completely lost the roof, and so has the fear. the prophet, like the baldest one, having naturally gorged himself on stale fly agarics, jumps on a plane and decides with his own eyes to find out who this bad bastard killed a couple of his guys and for what? even at the beginning of the series, and flies off to the island. the psycho disappeared somewhere, which is the most interesting thing. let's continue. a flying core of squids arrives and begins to scare everyone and everything on the aircraft carrier. As a result, the nomad inserts a cradle into them, drowns the flying core and the aircraft carrier itself. everyone who survived escaped on rotorcraft. goodbye titanic. As a result, the nomad drilled everyone and silently disappeared. look at the next picture. crisis 2. the prophet, having recovered from the lethal dose of fly agarics and climbed all the dungeons from a great hangover, simultaneously distributing stars from heaven and manna to the foreign invaders. understands that these scoundrels have dug in specifically. Ultimately, the prophet was released and he finally emerged into the light of day somewhere in the vicinity of New York. Well, then it’s clear to everyone. The swine flu epidemic is no joke. 1 point. Yes, the prophet took off his suit, and he gave it to the half-dead Alcatraz. if you believe the rumors, the prophet did not have a simple suit, but the very latest modification; therefore, it is not a fact that he took it off completely painlessly. in the video when he shoots a bullet into his dome, we see that instead of a suit the prophet was wearing a kind of tights that apparently did not allow him to fuse tightly with the suit. (Whoever watched the videos carefully remembers the moment when the medic looked at the data of the half-dead carcass of Alcatraz on the screen exclaims - that the suit actually fuses with the skin and tissues of the wearer, apparently that same tights was the prophet’s trump card “to remove the suit painlessly”, but in order to break the mental connection with the suit, you need to put a bullet in the pumpkin, otherwise the suit will not recognize the new owner, that is. carrier). Then the whole game is ruled by Alcatraz (everyone has already forgotten about the nomad and the psycho, apparently they also grabbed stale fly agarics and they are still pinned and squashed somewhere) crisis 2 is over, everything is in trouble, Alcotraz finally breaks the tower and he turns into a prophet. witchcraft, however, or maybe he hit it on his head when he fell from the sky and it was the 5th arrival that hit him. Next is the long-awaited crisis 3. The prophet is also Alcatraz, or the devil knows what’s in that tin. we see him in an iron coffin twitching in convulsions. The question is when did he have time and who rolled him into this coffin? (apparently they ate some stale fly agaric mushrooms again and finally found some adventures for themselves) and then, PSYCH appears in person! the battered Briton had aged considerably, swollen in places and swam, and naturally had already sown his nano-suit somewhere (it seems like the miracle grass wouldn’t let go of him for a long time). where has he been climbing all this time? Okay, let's continue playing, look at the plot, and reveal gaps in memory. but the trouble is that the nomad disappeared and did not appear in either the third part or the third and not a single hint (apparently the fly agarics turned out to be first-class) and how can we draw a conclusion? if you play all the parts, there are a lot of inconsistencies and witchcraft, although in general the picture is quite consistent from start to finish. but where is your wave after all, nomad? my personal opinion. the developers did not rush with the appearance of the nomad and left it for dessert, since it had already happened since the warhead crisis, and given that the game engine has become much thicker and has acquired all sorts of gadgets on a technically universal scale, you can understand that there is a possibility that the developers will pump it out after all nomad from the miracle of grass and fly agarics and will be brought out into the fresh air in the next episode, which will nevertheless reveal to the world where this grief of James Bond was, in the likeness of the next crisis in Warhead 2. and before that, we can only guess what color of pig they will put on us next time.

Crisis of resistance

a decrease in the resistance of the ball with an increase in the speed of the oncoming flow at Reynolds numbers of Re close to the critical value of Re. (Drag crisis) 1.5 * 105. The phenomenon was established in 1912 by A. G. Eiffel, explained in 1914 by L. Prandtl. Since it contradicts the well-known fact that the resistance of a body increases proportionally to the square of the speed, it is also called the Eiffel-Prandtl paradox.
At Re, there is a laminar boundary layer, which breaks off in the vicinity of the midsection, while the separation zone covers the entire aft part of the ball, which causes significant pressure resistance.
At Re > Re*, the laminar flow regime in the vicinity of the midsection is replaced by a turbulent one; Compared to laminar, it has a more complete velocity profile and can withstand large positive pressure gradients. As a result, the separation point 5 of the boundary layer moves downstream, the transverse dimensions of the stagnant zone are reduced, and, although it increases somewhat, the total ball decreases due to a significant decrease in pressure resistance.
Prandtl confirmed his explanation with the results of experimental studies of the flow around two balls, one of which had a smooth surface, and a thin wire ring was installed on the frontal surface of the other to artificially turbulize the flow. Installation of the ring (turbulator) led to a shift of the flow separation point downstream from the section (φ) ≈ 80(°) with a laminar boundary layer to the section (φ) ≈ 100-120(°) and a decrease in the total resistance of the ball.
K. s. also occurs when moving at subsonic speeds of other poorly streamlined bodies with a smooth contour: a circular cylinder, ellipsoids, etc. For well-streamlined bodies (airfoils and others), it is practically not observed.

Aviation: Encyclopedia. - M.: Great Russian Encyclopedia. Editor-in-Chief G.P. Svishchev. 1994 .

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Ohm's law looks so simple that the difficulties that had to be overcome in establishing it are overlooked and forgotten. Ohm's law is not easy to test and should not be taken as an obvious truth; Indeed, for many materials this is not true.

What exactly are these difficulties? Is it not possible to check what a change in the number of elements of a voltaic column produces by determining the current at different numbers of elements?

The fact is that when we take a different number of elements, we change the entire circuit, because additional elements also have additional resistance. Therefore, it is necessary to find a way to change the voltage without changing the battery itself. In addition, different current values heat the wire to different temperatures, and this effect can also affect the current strength. Ohm (1787-1854) overcame these difficulties by taking advantage of the phenomenon of thermoelectricity, which was discovered by Seebeck (1770-1831) in 1822.

The phenomenon is observed when a junction made of two different materials is heated: a small voltage is excited, which can create a current. Seebeck discovered this effect by experimenting with antimony and bismuth plates, and used a coil with a large number of turns, inside which a small magnet was inserted, as a current detector. Seebeck observed the deflection of the magnet only when he pressed the plates together with his hands, and soon realized that the effect was caused by the heat of his hand. Then he began to heat the plates with a lamp and obtained a much greater deviation. Seebeck did not fully understand the effect he discovered and called it “magnetic polarization.”

Ohm used the thermoelectric effect as a source of electromotive force. With a constant temperature difference, the thermocouple voltage should be very stable, and since the current is low, no noticeable heating should occur. In accordance with these considerations, Ohm manufactured an instrument which, apparently, should be considered the first real instrument for research in the field of electricity. Before this, only crude instruments were used.

The upper cylindrical part of the Ohm device is a current detector - torsion balance, ab and a" b" - thermoelements made of two copper wires soldered to a transverse bismuth rod; m and m" - cups with mercury, to which thermocouples could be connected. A conductor was connected to the cups, the ends of which were each time stripped before being immersed in mercury.

Om was aware of the importance of purity of materials. He kept junction a in boiling water, and dropped junction a into a mixture of ice and water and observed the deflection of the galvanometer.

Ohm's typical German thoroughness and attention to detail can be contrasted with the almost boyish enthusiasm that Faraday displayed in his work. In physics, both approaches are needed: the latter usually gives impetus to the study of a question, and the former is required to carefully study it and build a rigorous theory based on accurate quantitative results.

Ohm used eight pieces of copper wire of varying lengths as conductors. At first he was unable to obtain reproducible results, but a week later he apparently adjusted the instrument and obtained a series of readings for each of the conductors. These readings were the angles of twist of the suspension thread at which the arrow returned to zero. Ohm showed that with proper choice of constants A and B, the length x and the angle of twist X of the thread are related by the relation X = (A / B+ z)

You can illustrate this relationship by plotting x versus 1/X.

Ohm repeated his experiment with brass wire and obtained the same result with a different value of A and the same value of B. He took temperatures of 0 and 7.5 ° according to Reaumur (9.4 ° C) for the thermoelement junctions and found that the deviations he recorded decreased by about 10 times.

Thus, if we assume that the voltage produced by the device is proportional to the temperature difference - as we now know is approximately true - then it turns out that the current is proportional to this voltage. Ohm also showed that the current is inversely proportional to a certain quantity depending on the length of the wire. Ohm called it resistance, and it must be assumed that the quantity B represents the resistance of the rest of the circuit.

Thus Ohm showed that current is proportional to voltage and inversely proportional to the impedance of the circuit. This was a remarkably simple result for a complex experiment. At least that’s how it should seem to us now.

Ohm's contemporaries, especially his compatriots, thought differently: perhaps it was the simplicity of Ohm's law that aroused their suspicion. Om encountered difficulties in his career and was in need; Om was especially depressed by the fact that his works were not recognized. To the credit of Great Britain, and especially the Royal Society, it must be said that Ohm's work received well-deserved recognition there. Om is among those great men whose names are often found written in small letters: the name "om" was given to the unit of resistance.

G. Linson "Great Experiments in Physics"