Formation of the foundations of the theory of electrical circuits and electromagnetism

As is known, the processes in the electrical circuit are determined by the scalar values ​​of the electromotive force (or voltage) and current. The concept of electromotive force was put into circulation by A. Volta.

After the first qualitative and quantitative research in the 20s of the last century, the physical foundations of the theory of electric currents began to be formed. The largest contribution was made here by Ampere. GS Om with his famous law, obtained experimentally, laid the foundations for the calculation of electrical circuits. Even before Kirchhoff, young people had currents in branching chains (for example, Lenz). But only Kirchhoff in 1845-1847. It was possible to formulate known topological laws, named after him. Kirchhoff's laws formed the basis of all subsequent methods for calculating chains.

English physicist Charles Wheatstone (1802-1875 gg.) In connection with the work on improving the telegraph was looking for ways to measure resistance. As a result, he created the famous "Wheatstone bridge", the decisive advantage of which was the independence of the state of equilibrium from the voltage of the power source. In 1840 he showed his device BS Jacobi, and in 1843 gave a description of his "bridge" in the article. To change the resistance of one of the bridge's shoulders, Wheatstone applied adjustable resistors, which he called rheostats. Later (in 1860), Werner Siemens constructed a resistance store.

One of the largest German scientists Herman Ludwig Helmholtz (1821 - 1894) introduced in 1853 in the theory of chains the previously known in physics superposition principle, on the basis of which important theorems of electrical circuits were constructed, including the theorem on the equivalent source (Helmholtz-Thevenen) . Helmholtz, for the first time, obtained the equation of the transient process in the circuit when it was connected to the source, considered the time constants of the electrical circuit. William Thomson (Lord Kelvin) in 1853 gave a calculation of the oscillatory process and established a connection between the frequency of natural oscillations, inductance and capacitance.

Maxwell developed a method of contour currents, a theorem of reciprocity is proved. Gradually, practically the whole arsenal of calculation methods (including equivalent transformations) of DC circuits was formed.

After the discovery of electromagnetic induction, the attention of scientists was largely switched from "galvanic" currents, when the main objects of research were galvanic elements themselves, electrolysis processes, induction currents, when the phenomena of electromagnetism became most interesting.

Here a special role belongs to the outstanding Russian physicist E. X. Lenz. He studied in his hometown of Tartu (the former city of Yuriev, then Dorpat), as a student as a physicist participated in a round-the-world trip under the command of OE Kotzebue, became an academician of the Petersburg Academy of Sciences, head of the physics department, then dean of the physics and mathematics faculty, And in 1863 was elected rector of St. Petersburg University.

In his report to the Petersburg Academy of Sciences on Nov. 29, 1833, E. X. Lentz, being impressed by the works on electromagnetic induction by M. Faraday, gave his famous formulation of the law, named after him: "If a metal conductor moves near a galvanic current or The galvanic current of such a direction is excited in it, that it could cause, in the case of the immovability of a given conductor, its movement in the opposite direction, and it is assumed that such a movement can occur only in the direction of motion or in the direction opposite to that. "

It is obvious that in this formulation there is also the idea of ​​the principle of reversibility of electric machines developed later by B. S. Jacobi.

E. X. Land was one of the founders of the theory of magnetoelectric machines. He discovered and explained the phenomenon of armature reaction (1847) and established the need to move the brush from a geometric neutral, he first studied the phase shift of the current relative to the voltage phase (1853), invented a commutator to study the shape of the induction current curve (1857) . He established the condition for the regime of the maximum useful power of the energy source when the internal resistance of the source is equal to the resistance of the external circuit. E. Lenz's work on the thermal action of current (1842-1843), which was carried out independently of James Joule (1841), was so well known that it was a thorough investigation that the name of both scientists was fairly given the name of the law.

In 1867, Maxwell made a report to the Royal Society of London "On the theory of maintaining electrical currents mechanically without the use of permanent magnets." It was a purely theoretical work, covering all the known information about electric DC machines at the time. Probably, difficulties in understanding the Maxwellian style of presentation prevented contemporaries from appreciating this work.

Seriously advanced the theory of electrical machines introduced in 1879 by the British electrical engineer John Hopkinson (1849-1898) graphic representations of dependencies in electric machines, the so-called characteristics of machines (idling, external, etc.). He also introduced the concept of the coefficient of magnetic scattering.

In May 1886, J. and E. Hopkinsow made a report in the Royal Society of London "Dynamoelectric Machines", which contained a completely finished, not lost its meaning to the present time, the theory of electric DC machines.

The discoveries in the field of electricity and magnetism made in the first half of the nineteenth century, as well as the practical application of these phenomena, became prerequisites for important scientific generalizations, in particular the creation of Maxwell's electromagnetic theory. The first differential field equations were written down by Maxwell in 1855-1856. In 1864, he defined the electromagnetic field and laid the foundations of his theory.

The merit of Maxwell is that, using the huge experimental material accumulated before him, he generalized and developed the progressive ideas of Faraday, giving them a harmonious mathematical form.

In his work "Treatise on Electricity and Magnetism" (1873), Maxwell laid out the foundations of his field theory, which is the cornerstone of the modern theory of electromagnetism. The most important results of his research Maxwell formulated in the form of famous equations that received his name. Maxwell generalized the law of electromagnetic induction, extending it to an arbitrary contour in any medium. He introduced the concept of electric displacement and displacement currents, established the principle of closed current.

One of Maxwell's most important conclusions is the assertion that the magnetic and electric fields are closely interconnected and the change of one of them causes the appearance of the other. Studies have shown that the speed of propagation of such electromagnetic disturbances coincides with the speed of light. This conclusion was the basis of the electromagnetic theory of light developed by Maxwell and is one of the outstanding theoretical generalizations of natural science.

Maxwell did not live to see the triumph of his deep scientific ideas and generalizations. He himself could not yet fully imagine the meaning of all that was contained in his Treatise on Electricity and Magnetism, and what came of it. Later, the German physicist H. Hertz experimentally proved the existence of electromagnetic waves, and the Russian physicist PN Lebedev discovered light pressure and determined from experiments its value, which coincides with the one calculated according to Maxwell's theory.

Important work in the development of ideas about the motion of energy was the work of prof. NA Umov, among which his doctoral thesis "Equations of the motion of energy in bodies" (1874) deserves special attention. Umov's ideas were further developed, in particular, in the works of the English physicist J. G. G. Poyntinga applied to the electromagnetic field (1884).

Veselovsky O. N. Shneberg A. Ya "Essays on the history of electrical engineering"