Basic law of electrostatics. History and essence of scientific discovery

MOST IMPORTANT SCIENTIFIC DISCOVERIES
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Basic law of electrostatics. History and essence of scientific discovery

The most important scientific discoveries

Directory / The most important scientific discoveries

Electrical phenomena gradually lost their original character of isolated, amusing natural phenomena and gradually formed a kind of unity, which existing theories tried to cover with several basic principles. It was time to move from qualitative to quantitative research.

This direction of research is clearly expressed in the work of 1859 by the St. Petersburg academician F. Epinus (1724–1802).

Aepinus bases his mathematical consideration on the following principles: every body has in its natural state a well-defined amount of electricity. Particles of the electric fluid are mutually repelled and attracted to ordinary matter. Electrical effects appear when the amount of electrical fluid in the body is greater or less than what should be in the natural state.

Aepinus makes the assumption: "... I still do not dare to determine these functional dependencies. However, if it were necessary to make a choice between different functions, then I would willingly argue that these quantities change inversely with the squares of the distances. This can be assumed with some plausibility , for in favor of such a dependence, apparently, speaks analogy with other natural phenomena. Aepinus was followed by Henry Cavendish (1731–1810), who in his paper of 1771 accepts Aepinus's hypotheses with one change: the attraction of two electric charges is assumed to be inversely proportional to some degree of distance, not yet specified.

Cavendish, using mathematical reasoning, concludes: if the force of interaction of electric charges obeys the inverse square law, then "almost all" the electric charge is concentrated on the very surface of the conductor. Thus, an indirect way of establishing the law of interaction of charges is outlined.

The main difficulty in establishing the "electric force law" was to find an experimental situation in which the ponderomotive forces would coincide with the forces acting between elementary charges.

Perhaps the correct approach to this problem was found first of all by the English naturalist J. Robison (1739–1805).

The experimental method used by Robison was based on the idea that interacting charges can be considered point charges when the dimensions of the spheres on which they are localized are much smaller than the distance between the centers of the spheres.

The installation with which the Englishman made measurements is described in his fundamental work "The System of Mechanical Philosophy". The work was published after his death, in 1822.

Given the measurement errors, Robison concluded:

"The action between the spheres is exactly proportional to the inverse square of the distance between their centers."

However, the basic law of electrostatics does not bear the name of Robison. The fact is that the scientist reported on the results obtained only in 1801, and described in detail even later. At that time, the works of the French scientist Pendant.

Charles Augustin Coulomb (1736–1806) was born in Angouleme in southwestern France. After the birth of Charles, the family moved to Paris.

At first, the boy attended the College of the Four Nations, also known as the College of Mazarin. Soon his father went bankrupt and left his family in Montpellier, in the south of France. The conflict between mother and son led to the fact that Charles left the capital and moved to his father.

In February 1757, at a meeting of the Royal Scientific Society of Montpellier, a young lover of mathematics read his first scientific work, "Geometric Essay on Mean Proportional Curves". Subsequently, Coulomb took an active part in the work of the society and presented five more memoirs - two in mathematics and three in astronomy.

In February 1760, Charles entered the Mézières School of Military Engineers. In November of the following year, Charles graduated from the School and was assigned to a major port on the west coast of France, Brest. Then he came to Martinique. During the eight years spent there, he was seriously ill several times, but each time he returned to his official duties. These diseases did not go unnoticed. After returning to France, Coulomb could no longer be considered a completely healthy person.

Despite all these difficulties, Coulomb performed his duties very well. His success in building a fort at Mont Garnier was marked by a promotion: in March 1770 he received the rank of captain - at that time it could be considered a very quick promotion. Soon, Coulomb fell seriously ill again and, finally, filed a report with a request to be transferred to France.

After returning to his homeland, Coulomb was assigned to Bushen. Here he completes a study begun during his service in the West Indies. Many of the ideas formulated by him in his very first scientific work are still considered fundamental by specialists in the strength of materials.

In 1774, Coulomb was transferred to the large port of Cherbourg, where he served until 1777. There, Coulomb was engaged in the repair of a number of fortifications. This work left a lot of time for leisure, and the young scientist continued his scientific research. The main topic that Coulomb was interested in at that time was the development of an optimal method for manufacturing magnetic needles for accurate measurements of the Earth's magnetic field. This topic was given in a competition announced by the Paris Academy of Sciences.

Two winners of the competition in 1777 were announced at once - the Swedish scientist van Schwinden, who had already put forward the work for the competition, and Coulomb. However, for the history of science, it is not the chapter of Coulomb's memoir devoted to magnetic needles that is of greatest interest, but the next chapter, where the mechanical properties of the threads on which the arrows are hung are analyzed. The scientist conducted a series of experiments and established the general order of dependence of the moment of torsion deformation force on the angle of twist of the thread and on its parameters: length and diameter.

The low elasticity of silk threads and hair with respect to torsion made it possible to neglect the arising moment of elastic forces and to assume that the magnetic needle exactly follows the declination variations. This circumstance served as an impetus for Coulomb to study the torsion of cylindrical metal threads. The results of his experiments were summarized in the work "Theoretical and experimental studies of the torsion force and elasticity of metal wires", completed in 1784.

The study of the torsion of thin metal threads, carried out by Coulomb for the competition of 1777, had an important practical consequence - the creation of a torsion balance. This instrument could be used to measure small forces of various natures, and it provided a sensitivity unprecedented in the XNUMXth century.

Having developed the most accurate physical device, Coulomb began to look for a worthy application for it. The scientist begins work on the problems of electricity and magnetism.

The most important result obtained by Coulomb in the field of electricity was the establishment of the basic law of electrostatics - the law of interaction of motionless point charges. The scientist formulates the fundamental law of electricity as follows:

"The repulsive force of two small balls, electrified by electricity of the same nature, is inversely proportional to the square of the distance between the centers of the balls."

Coulomb began by measuring the dependence of the repulsive force of like charges on distance and carried out numerous experiments. The scientist gives the results of three measurements, in which the distances between the charges were related as 36:18:172, and the corresponding repulsive forces - as 36:144:5751, i.e., the forces are almost exactly inversely proportional to the squares of the distances. In reality, the experimental data are somewhat different from the theoretical law. Coulomb considers the main reasons for the discrepancy, in addition to some simplifications adopted in the calculation, to be the leakage of electricity during the experiment.

The task of measuring the force of attraction turned out to be more difficult, since it is very difficult to prevent the moving ball of the balance from coming into contact with another charge of the opposite sign. Nevertheless, Coulomb quite often managed to achieve a balance between the attractive force of two balls and the opposing force of the twisted thread. The obtained experimental data indicated that the force of attraction also obeys the inverse square law.

But Coulomb was not satisfied with these results either. “To confirm this law, which, as he foresaw, would play a fundamental role in the theory of electricity,” writes M. Gliozzi, “Coulomb resorted to a new original method for measuring small forces, which had already been used earlier to measure the magnetic force of a steel point. This method turned out to be very effective and is now known as the "method of oscillation" It is based on the fact that, just as the frequency of oscillation of a pendulum depends on the magnitude of the force of gravity in a given place, so the frequency of oscillation of an electrified needle oscillating in a horizontal plane depends on the intensity electric force acting on it, so that this force can be found from the number of oscillations per second.To implement this plan, Coulomb caused an insulating rod to oscillate, equipped at the end with a small vertical charged plate and located in front of an insulated metal ball, charged opposite to the charge of the plate and located so, that one of its horizontal diameter ov passes through the center of the plate when it is in equilibrium. In this way, the inverse square law was also fully confirmed."

Thus, Coulomb laid the foundations of electrostatics. He obtained experimental results of both fundamental and applied importance. For the history of physics, his experiments with torsion balances were of great importance also because they gave physicists a method for determining the unit of electric charge through the quantities used in mechanics: force and distance, which made it possible to conduct quantitative studies of electrical phenomena.

Author: Samin D.K.

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