An electron is a subatomic particle that responds to both electric and magnetic fields.

Throughout the second half of the 19th century, physicists actively studied the phenomenon of cathode rays . The simplest apparatus in which they were observed was a sealed glass tube filled with rarefied gas, into which an electrode was soldered on both sides: on one side cathode, connected to the negative pole of the electric battery; with another - anode, connected to the positive pole. When high voltage was applied to the cathode-anode pair, the rarefied gas in the tube began to glow, and at low voltages the glow was observed only in the cathode region, and with increasing voltage - inside the entire tube; however, when the gas was pumped out of the tube, starting from a certain moment, the glow disappeared in the cathode region, remaining near the anode. Scientists attributed this glow cathode rays.

By the end of the 1880s, the discussion about the nature of cathode rays took on a sharp polemical character. The overwhelming majority of prominent scientists of the German school were of the opinion that cathode rays are, like light, wave disturbances of the invisible ether. In England, they were of the opinion that cathode rays consist of ionized molecules or atoms of the gas itself. Each side had strong evidence to support their hypothesis. Proponents of the molecular hypothesis rightly pointed to the fact that cathode rays are deflected under the influence of a magnetic field, while light rays are not affected by the magnetic field. Therefore, they consist of charged particles. On the other hand, supporters of the corpuscular hypothesis could not explain a number of phenomena, in particular the effect of almost unimpeded passage of cathode rays through thin aluminum foil discovered in 1892.

Finally, in 1897, the young English physicist J. J. Thomson put an end to these disputes once and for all, and at the same time became famous for centuries as the discoverer of the electron. In his experiment, Thomson used an improved cathode ray tube, the design of which was supplemented by electric coils that created (according to Ampere's law) a magnetic field inside the tube, and a set of parallel electric capacitor plates that created an electric field inside the tube. Thanks to this, it became possible to study the behavior of cathode rays under the influence of both magnetic and electric fields.

Using a new tube design, Thomson showed successively that: (1) cathode rays are deflected in a magnetic field in the absence of an electric one; (2) cathode rays are deflected in an electric field in the absence of a magnetic field; and (3) under the simultaneous action of electric and magnetic fields of balanced intensity, oriented in directions that separately cause deviations in opposite directions, the cathode rays propagate rectilinearly, that is, the action of the two fields is mutually balanced.

Thomson found that the relationship between the electric and magnetic fields at which their effects are balanced depends on the speed at which the particles move. After conducting a series of measurements, Thomson was able to determine the speed of movement of the cathode rays. It turned out that they move much slower than the speed of light, which meant that cathode rays can only be particles, since any electromagnetic radiation, including light itself, travels at the speed of light ( cm. Spectrum of electromagnetic radiation). These unknown particles. Thomson called them “corpuscles,” but they soon became known as “electrons.”

It immediately became clear that electrons must exist as part of atoms - otherwise, where would they come from? April 30, 1897 - the date of Thomson's report of his results at a meeting of the Royal Society of London - is considered the birthday of the electron. And on this day the idea of the “indivisibility” of atoms became a thing of the past ( cm. Atomic theory of the structure of matter). Coupled with the discovery of the atomic nucleus that followed a little over ten years later ( cm. Rutherford's discovery of the electron laid the foundation for the modern model of the atom.

The “cathode” tubes described above, or more precisely, cathode ray tubes, became the simplest predecessors of modern television picture tubes and computer monitors, in which strictly controlled quantities of electrons are knocked out from the surface of a hot cathode, under the influence of alternating magnetic fields they are deflected at strictly specified angles and bombard the phosphorescent cells of the screens , forming a clear image on them, resulting from the photoelectric effect, the discovery of which would also be impossible without our knowledge of the true nature of cathode rays.

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"The History of the Discovery of the Electron"

Prerequisites for discovery, hypotheses

In 1749, Benjamin Franklin hypothesized that electricity is a kind of material substance. He assigned the central role of electrical matter to the idea of the atomic structure of the electrical fluid. The terms charge, discharge, positive charge, negative charge, capacitor, battery, particles of electricity first appear in Franklin's works.

Johann Ritter in 1801 proposed the idea of a discrete, granular structure of electricity.

Wilhelm Weber, in his works since 1846, introduces the concept of the atom of electricity and the hypothesis that its movement around the material core can be explained by thermal and light phenomena.

Michael Faraday coined the term "ion" for the carriers of electricity in an electrolyte and proposed that the ion has a permanent charge. G. Helmholtz showed in 1881 that Faraday's concept must be consistent with Maxwell's equations. George Stoney in 1881 first calculated the charge of a monovalent ion during electrolysis, and in 1891, in one of his theoretical works, Stoney proposed the term “electron” to denote the electrical charge of a monovalent ion during electrolysis.

History of the discovery of the electron

When Leucippus and his student Democritus first introduced the concept of “atom,” they imagined it as a finite, indivisible particle of matter. More than two millennia later, Dalton supported this view. According to this definition, an atom must have no internal structure. After all, if an atom can be divided into smaller particles, then these particles will be true atoms.

Throughout the 19th century. the atom was considered indivisible, devoid of any characteristic features and having no internal structure. However, after conducting a series of experiments that were not even chemical in nature, this point of view was rejected. The study of electric current led to the breaking of old ideas.

As you know, an electrical voltage is established between positively and negatively charged points. Under the influence of such a voltage, charges move from a point with a higher potential to a point with a lower potential. Thus, an electric current arises, which tends to equalize the potential difference between two points of the electric field.

The first researchers of electricity, in their not yet very seriously substantiated experiments, established that some liquids, such as salt solutions, conduct electric current relatively easily. Lightning, an electrical discharge generated during a thunderstorm, instantly spreads through a layer of air several kilometers deep.

Experimenters of the 19th century it seemed very tempting to try to pass current through a vacuum. But for the results of such an experiment to be reliable, it was necessary to obtain a sufficiently deep vacuum. Faraday's attempts to pass electric current through a vacuum failed only because he was unable to obtain a deep enough vacuum.

In 1855, the German glassblower Heinrich Geisler made glass vessels of a special shape and vacuumized them using the method he invented. His friend, the German physicist and mathematician Julius Plücker, used these Heussler tubes to study electrical discharges in vacuum and gases.

Plücker soldered electrodes into the day tubes, created an electric potential between them and received an electric current. Under the influence of current, a glow appeared in the tubes (“incandescent effect”), the nature of which depended on the depth of the vacuum. At a sufficiently deep vacuum, the glow in the tube disappeared, and only near the anode was a green glow of the tube glass noticeable.

Around 1875, the English physicist William Crookes (1832-1919) designed tubes in which a deeper vacuum could be obtained (Crookes tubes). It has become more convenient to study electric current passing through a vacuum. It seemed quite obvious that an electric current originated at the cathode and moved to the anode, where it struck the glass surrounding the anode and created a glow. To prove the validity of this understanding of the phenomenon, Crookes placed a piece of metal in the tube, and a shadow appeared on the glass at the end opposite to the cathode. However, at that time, physicists did not know what electric current was. They could not quite definitely say what was actually moving from the cathode to the anode, although they knew for certain that this flow was moving in a straight line (since the shadow of the metal was clearly defined). Without reaching any conclusion regarding the nature of this phenomenon, physicists classified it as “radiation,” and in 1876 the German physicist Eugen Goldstein (1850–1930) called this flow cathode rays.

It is natural to assume that cathode rays are some form of light that has a wave nature. Waves, like light, travel in a straight line and, like light, are not influenced by gravitational forces. At the same time, cathode rays may well represent particles moving at enormous speed. Because the mass of these particles is extremely small or because they move extremely quickly (or for both reasons), they either do not experience the effect of gravity at all, or this effect does not manifest itself to any appreciable extent. For several decades, scientists could not reach a consensus regarding the nature of cathode rays. Moreover, German physicists strongly advocated considering cathode rays as oscillations, and English physicists equally resolutely insisted that cathode rays are particles.

This dispute could be resolved by trying to establish whether cathode rays are deflected by a magnetic field.

Plücker himself and, independently of him, Crookes showed that such a deviation exists. One more question remained to be resolved. If cathode rays are charged particles, then the electric field should also deflect them. However, it was not immediately possible to prove that cathode rays are deflected in an electric field. Only in 1897, the English physicist Joseph John Thomson (1856-1940), working with tubes with a very deep vacuum, was finally able to show that cathode rays are deflected under the influence of an electric field.

Rice. 1

This was the last link in the chain of evidence, and now all that remained was to agree with the fact that cathode rays are a stream of negatively charged particles. The amount of deflection of a particle in a magnetic field of a given strength is determined by the mass of the particle and the magnitude of its electric charge. Thomson was able to measure the ratio of the mass and charge of a particle, although he could not measure these quantities separately.

As is known, the hydrogen atom has the smallest mass, and if we assume that a particle of cathode rays has the same mass, then its electric charge should be hundreds of times greater than the smallest known charge (the charge of a hydrogen ion). At the same time, if we assume that the charge of a particle of cathode rays is equal to the minimum charge observed in ions, then in this case the mass of the particle should be many times less than the mass of the hydrogen atom. Since Thomson determined only the ratio of mass and charge, both options were equally probable.

Nevertheless, there were good reasons to believe that the cathode ray particle was much smaller than any atom. In 1911, the American physicist Robert Andrews Millikan (1868-1953) measured, quite accurately, the minimum electric charge that a particle can carry, and thereby proved the validity of this assumption.

If a cathode ray particle carries such a minimal charge, its mass must be only 1/1837 that of a hydrogen atom. Thus, the first of the subatomic particles was discovered.

Ever since the discovery of Faraday's laws of electrolysis, there has been an idea that electricity can be carried by particles. In 1891, Irish physicist George Johnston Stoney even proposed a name for the basic unit of electricity; he proposed calling it the electron. So, as a result of the study of cathode rays, the “atom of electricity” was discovered, which scientists have been thinking about and wondering about for more than half a century. Given the importance of J. J. Thomson's work, he can be considered the discoverer of the electron.

Thomson's experiment

Since 1895, Joseph John Thomson at the Cavendish Laboratory at the University of Cambridge began a methodical quantitative study of the deflection of cathode rays in electric and magnetic fields. The results of this work were published in 1897 in the October issue of Philosophical Magazine. In his experiment, Thomson proved that all particles that form cathode rays are identical to each other and are part of the substance. The essence of the experiments and the hypothesis about the existence of matter in a state of even finer fragmentation than atoms was presented by Thomson at the evening meeting of the Royal Society on April 29, 1897. An extract from this message was published in the Electrican on May 21, 1897. For this discovery, Thomson in 1906 received the Nobel Prize in Physics.

Thomson's experiment involved studying beams of cathode rays passing through a system of parallel metal plates that created an electric field and systems of coils that created a magnetic field. It was discovered that the beams were deflected when both fields were applied separately, and at a certain ratio between them, the beams did not change their straight trajectory. This field ratio depended on the particle speed. After carrying out a series of measurements, Thomson found out that the speed of movement of particles is much lower than the speed of light - thus it was shown that particles must have mass. Next, it was suggested that these particles are present in atoms and a model of the atom was proposed, which was subsequently developed in Rutherford’s experiments.

Thomson's model.

Rice. 2 Thomson model

Thomson's merit was the proof that all particles that form cathode rays are identical to each other and are part of the substance. Using a special type of discharge tube, Thomson measured the speed and charge-to-mass ratio of cathode ray particles, later called electrons. Electrons flew out of the cathode under the influence of a high-voltage discharge in the tube. Only those flying along the axis of the tube passed through diaphragms D and E.

Charge to mass ratio. Tube used by the English physicist J. Thomson to determine the charge-to-mass ratio for cathode rays. These experiments led to the discovery of the electron.

In normal mode, these electrons hit the center of the luminescent screen. (Thomson's tube was the first "cathode ray tube" with a screen, a precursor to the television picture tube.) The tube also contained a pair of electric capacitor plates which, when energized, could deflect electrons.

In addition, a magnetic field could be created in the same area of the tube using a pair of current-carrying coils, capable of deflecting electrons in the opposite direction. The force exerted by the magnetic field is proportional to the field strength, the speed of the particle and its charge. Thomson adjusted the electric and magnetic fields so that the total deflection of the electrons was zero, i.e. the electron beam returned to its original position. electron atom thompson franklin

Thomson found that this speed depends on the voltage across the tube and that the kinetic energy of the electrons is directly proportional to this voltage. By combining the equations with an expression for the speed of the electron, he found the ratio of charge to mass.

Thomson's experiments showed that electrons in electrical discharges can arise from any substance. Since all electrons are the same, elements must differ only in the number of electrons. In addition, the small value of the electron mass indicated that the mass of the atom was not concentrated in them. J. Thomson, who made a huge contribution to the experimental study of the structure of the atom, sought to find a model that would explain all its known properties. Since the predominant proportion of the mass of an atom is concentrated in its positively charged part, he assumed that the atom is a spherical distribution of positive charge with a radius of approximately 10-10 m, and on its surface there are electrons held by elastic forces that allow them to oscillate (Fig. 3). The net negative charge of the electrons exactly cancels out the positive charge, so that the atom is electrically neutral. The electrons are on the sphere, but can perform simple harmonic oscillations relative to the equilibrium position.

Rice. 3 The atom according to Thomson's model (the model is known as "Raisin Pudding")

Such oscillations can occur only at certain frequencies, which correspond to narrow spectral lines observed in gas-discharge tubes. Electrons can be knocked out of their positions quite easily, resulting in positively charged "ions" that make up the "channel beams" in mass spectrograph experiments. X-rays correspond to very high overtones of the fundamental vibrations of electrons. Alpha particles produced during radioactive transformations are part of the positive sphere, knocked out of it as a result of some energetic tearing of the atom. Electrons are held inside a positively charged sphere by elastic forces. Those of them that are on the surface can be “knocked out” quite easily, leaving an ionized atom. However, this model raised a number of objections.

The discovery of the electron had a tremendous impact on the development of modern physics, leading to the discovery of the mechanism of radiation and absorption of electromagnetic energy, the mechanism of interaction of electromagnetic waves with matter. The electron has today become the foundation of a grandiose edifice of electronics.

The electron turned out to be not only an object, but also a means of emitting the properties of matter. A clear example of this is the rapid development of accelerator technology.

References

1) http://allchem.ru/pages/history/104

2) https://ru.wikipedia.org/wiki/%D0%9E%D1%82%D0%BA%D1%80%D1%8B%D1%82%D0%B8%D0%B5_%D1%8D %D0%BB%D0%B5%D0%BA%D1%82%D1%80%D0%BE%D0%BD%D0%B0

3) http://element y.ru/trefil/19

4) http://www.krugosvet.ru/enc/nauka_i_tehnika/fizika/FIZIKA

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J.J. Thomson and his contribution to the development of physics
XX century

To the 150th anniversary of his birth

One hundred and fifty years ago in England, in the family of a Manchester second-hand book dealer, a boy was born who became one of the most prominent physicists of the late 19th and early 20th centuries. This happened on December 18, 1856, and this child was Joseph John Thomson. His contribution to the development of physics is impressive: the experimental discovery of the electron in 1897, awarded the Nobel Prize in Physics (1906); one of the first models of the atom to include electrons (1903); the first experimental evidence of the existence of isotopes (1912), the creation of a large scientific school of physicists, the most prominent representative of which is Ernest Rutherford - this is not a complete list of what this man did in science during his long life. That is why, in the year of his anniversary, it is important not only to remember his scientific heritage, but also to try to assess the significance of this heritage for our time. And there is one more reason. In the minds of many people - both professional physicists and those simply interested in the history of science - the name of this scientist, whom his contemporaries briefly called “Gi-Gi”, on the one hand, is often overshadowed by the names of many other outstanding physicists of the past century, and on the other hand, he is sometimes mistakenly credited with the scientific merits of his older contemporary, William Thomson (1824–1907), who received the title of Lord Kelvin in 1892 for his outstanding scientific achievements (note that the latter not only proposed the absolute temperature scale, but also established 1853 Thomson’s formula for the period of oscillation in an oscillatory circuit, now studied in school). This circumstance is also the reason why J. J. Thomson deserves special mention.

In his youth, Thomson wanted to become an engineer and even entered one of the Manchester colleges of the relevant profile. But soon, due to the death of his father, he was forced to interrupt his engineering studies due to lack of funds. “However, having studied mathematics, physics and chemistry, in 1876 he managed to receive a scholarship to Trinity College, and it was with the University of Cambridge that Thomson’s entire further academic life was connected.” (*Word " Trinity"translated from English. means "Trinity", i.e. Trinity College is the College of St. Trinity.")

Thomson graduated from University in 1880, and his first scientific works date back to this time (early 90s of the 19th century). They are devoted to the development of Maxwell's electrodynamics. Thus, solving the problem of the motion of a charged ball, Thomson came to the conclusion that the apparent mass of the charge increases due to the energy of the electrostatic field, and this conclusion was further developed at the beginning of the twentieth century. in the special theory of relativity, in particular, in the works of A. Poincaré. In 1884, at the age of 28, Thomson became director of the Cavendish Laboratory, replacing J. W. Rayleigh in this post, and the directorship continued until 1918. A year later, in 1885, Thomson defended his dissertation entitled “On Some applications of the principles of dynamics to physical phenomena,” which G. Hertz later called “a wonderful treatise”: “The author develops here the consequences of dynamics, which, along with Newton’s laws of motion, are based on new, not clearly expressed premises. I could join this treatise; in fact, my own research had already advanced significantly before I became acquainted with this treatise,” Hertz wrote about Thomson’s dissertation in the last year of his life in the preface to the book “Principles of Mechanics Set forth in a New Connection” (1894).

Discovery of the electron

1. Background. In his article “The Scientific Activity of Benjamin Franklin” (1956), academician P.L. Kapitsa quotes a fragment of one of his letters dated 1749: “Electrical matter consists of extremely small particles, because they can penetrate ordinary substances, as dense as metal, with such ease and freedom that they experience no noticeable resistance.” Commenting on these words, P.L. Kapitsa writes: “Nowadays we call these “extremely small particles” electrons. Franklin further considered any body as a sponge saturated with these particles of electricity. The electrification of bodies consists in the fact that a body that has an excess of electrical particles is positively charged; if a body lacks these particles, it is negatively charged.”

Thus, guesses about the existence of particles that are carriers of electric charge were expressed back in the 18th century. The first attempt to construct electrodynamics based on the idea of the granular structure of the “electric fluid” was made in the 40s. XIX century German physicist Wilhelm Eduard Weber (1804–1891), who considered these particles to be weightless and called them “electric masses,” essentially equating the term “mass” with the term “charge.” In Maxwell's electrodynamics, which he developed mainly in the 60s. XIX century particles of this kind are not mentioned: the field approach dominates in it, and electricity is treated as some kind of incompressible fluid moving in conductors. An attempt to introduce the idea of discreteness of electric charges into Maxwell's electrodynamics was made for the first time in 1878 by G. Lorentz. Thus, in 1892, in his work “Maxwell’s Electromagnetic Theory and Its Application to Moving Bodies,” Lorenz wrote: “It will be sufficient to assume that all weighty bodies contain many small particles charged positively or negatively, and that all electrical phenomena are caused by the displacement of these particles . According to this concept, the electric charge is due to an excess of particles of one specific sign, the electric current is due to the flow of these particles, and in solid insulators there is a “dielectric displacement” if the electrified particles contained in them are removed from their equilibrium positions.

These hypotheses contain nothing new in relation to electrolytes, and they represent a certain analogy with the ideas regarding metallic conductors that existed in the old theory of electricity. It’s not so far from the atoms of the electric liquid to the charged corpuscles.”

Particularly noteworthy are studies concerning the characteristics of electrical phenomena in rarefied gases. In the 70s German physicist Eugen Goldstein (1850–1930) introduced the concept of cathode rays into physics and suggested that in their nature they are similar to light with the only difference that light is emitted by the body around itself in all directions, and cathode rays are emitted only perpendicular to the surface of the cathode, but Both processes are wave processes by nature. Goldstein's experiments in the late 70s. XIX century was repeated in an improved form by the outstanding English physicist William Crookes (1832–1919). Having introduced a radiometer into the gas-discharge tube, which he had designed back in 1873, Crookes discovered its rotation under the influence of cathode rays, from which he concluded that these rays transfer energy and momentum. Having placed a metal cross in the tube in the path of the cathode rays, Crookes discovered its shadow on the fluorescent glass of the tube and came to the conclusion that the cathode rays propagated in a straight line. He was experimentally convinced that these rays can be deflected in one direction or another by a magnet. He called the rays something fourth or ultragaseous state of matter, or radiant matter, which, however, has a corpuscular nature, interpreted on a cosmic scale: “When studying this fourth state of matter, the idea is created that we finally have at our disposal the “final” particles, which we can rightfully consider to be the basis of the physics of the Universe.”

The corpuscular concept of the nature of cathode rays was opposed by the already mentioned wave concept. Crookes believed that cathode rays are molecules of residual gas contained in a gas-discharge tube; Having come into contact with the cathode, they receive a negative charge from it and are repelled from the cathode. But then they must be deflected by the electric field. The experiments conducted by G. Hertz showed that they are not deflected by an electric field. In 1892, Hertz experimentally became convinced that cathode rays could pass through thin aluminum plates. But if this is so, then it is not clear how electrified molecules can pass through metal. On the other hand, a magnetic field does not affect light waves, but Crookes' experiments showed that this field acts on cathode rays. Thus, in the early 90s. XIX century there was a problem that needed resolution. What are cathode rays - waves or particles?

2. J. Perrin and J. Thomson - solution to the problem of the nature of cathode rays. In Fig. Figure 1 shows a diagram of the experiment that was carried out in 1895 by Jean Baptiste Perrin (1870–1942). Inside the discharge tube in front of the cathode N a metal cylinder connected to the electroscope was placed at a distance of 10 cm ABCD(jacketed EFGH) with a small hole opposite the cathode. When the tube was operating, a beam of cathode rays penetrated the cylinder, and the cylinder always received a negative charge. If a magnet was used to deflect the cathode rays so that they did not enter the cylinder, the electroscope did not give any readings. From this it could be concluded that cathode rays carry negative electrical charges, and therefore we are talking about a flow of particles.

However, supporters of the wave concept put forward the following objection. While admitting that the cathode could emit charged particles, they denied that these particles were cathode rays. When the cathode rays hit the wall of the tube, the latter began to glow, but the glow and the ejection of particles by the cathode, in their opinion, could be two different phenomena, just as the departure of an artillery shell from the barrel of a gun and the flash accompanying this process are different phenomena.

It was necessary to experimentally prove that the ejection of charged particles by the cathode and the glow of the wall of the discharge tube are interconnected, that we are not talking about different physical phenomena, but about one. This evidence was presented by J.J. Thomson in his experiments in 1897, which were variants of Perrin's experiments. The cylinder with the hole was located not in front of the cathode, but on the side of it, for which the geometry of the tube itself was changed, Fig. 2. In this case, fluorescence was initially observed in the glass wall of the tube, but it disappeared when the cathode rays were deflected by a magnet and “led” into the hole of a cylinder connected to an electroscope, which recorded a negative charge. Thus, it was proven that the glow of the tube wall and the charging of the cylinder are caused by the same particles. And besides, in his experiments Thomson managed to do what Hertz failed to do: he managed to achieve the deflection of cathode rays by an electric field (in Hertz’s experiments, everything was spoiled by the conductivity of the residual gas in the tube, which arose under the influence of cathode rays).

So cathode rays are particles. Which? What are their properties, their features? Thomson answered these questions by describing their movement with the laws of mechanics. For example, in an electrostatic field they should behave in the same way as falling bodies behave near the surface of the Earth. If, for example, a positively charged particle finds itself in the space between two horizontal plates, the upper one of which is positively charged and the lower one negatively charged, then this particle will be repelled from the upper plate and attracted to the lower one, i.e. move with acceleration downwards. If this particle flies into the space between these plates with a speed directed parallel to the planes of the plates, then it will approach the lower plate along a parabolic trajectory, i.e. move in the same way as a stone thrown at a speed parallel to the earth’s surface falls on the surface of the Earth. If in the space between the plates there is also a magnetic field directed either beyond the drawing or from the drawing, then, firstly, the Lorentz force (magnetic force) will act on the charged particle under study, and by its direction one can judge the sign of the charge, and secondly, electric and magnetic forces can cancel each other out if they are directed in opposite directions. The electric force is calculated as the product of the particle charge and the electric field strength; the magnetic force is calculated as the product of this charge by the speed of the particle and the induction of the magnetic field (let the angle between the velocity and induction vectors be 90°). Then we get eE = eB, i.e. E = B. From here it is immediately clear that the speed of movement of a charged particle is calculated as the ratio of the electric field strength E to magnetic field induction B. However, it is known that the Lorentz force imparts centripetal acceleration to a charged particle 2 / r; then you can find the value of the specific charge of the particle, i.e. ratio of charge to particle mass:

From this result the following can be seen. The specific charge of the particle under study depends on the magnetic field induction and the electric field strength (i.e., on the potential difference between the plates). The specific charge of a particle does not depend on the chemical properties of the residual gas in the tube, on the geometric shape of the tube, on the material from which the electrodes are made, on the speed of the cathode rays (in Thomson's experiments in 1897, this speed was 0.1 With, Where With– speed of light in vacuum) and not on any other physical parameters. Cathode rays are not residual gas ions emitted from the cathode, as Crookes believed, but they are still particles. And if their specific charge is constant, then we are talking about identical particles. Expressing the mass of these particles in grams and the charge in SGSM, as was customary in those days, Thomson obtained the specific charge of the particles equal to 1.7 10 7 units. SGSM/g. The high accuracy of his experiment is evidenced by the fact that the modern value of the specific charge of an electron is (1.76 ± 0.002)10 7 units. SGSM/g.

Based on the obtained value of the specific charge, one could try to estimate the mass of the particles. By the time the experiments were carried out, the value of the specific charge of the hydrogen ion was already known (10 4 SGSM units/g). The term “electron” also existed by that time; it was introduced into use in 1891 by the Irish physicist and mathematician George Stoney (1826–1911) to designate the electric charge of a monovalent ion during electrolysis, and after Thomson’s research this term was transferred to the particles he discovered . And if we assume that the charge and mass of the electron are somehow related to the corresponding values for the hydrogen ion, then two options were possible:

A) the mass of the electron is equal to the mass of the hydrogen ion, then the charge of the electron must be greater than the charge of the hydrogen ion by 10 3 times. However, research by German physicist Philipp Lenard showed the unreality of such an assumption. He found that the average free path of particles forming cathode rays in the air is 0.5 cm, while for the hydrogen ion it is less than 10 –5 cm. This means that the mass of newly discovered particles should be small;

b) the charge of the particle is equal to the charge of the hydrogen ion, but in this case the mass of this particle should be 10 3 times less than the mass of the hydrogen ion. Thomson settled on this option.

Still, it would be better to somehow directly measure either the charge of the electron or its mass. The following circumstance helped solve the problem. In the same 1897, when Thomson carried out his experiments on the study of cathode rays, his student Charles Wilson found that in air supersaturated with water vapor, each ion becomes a center of steam condensation: the ion attracts droplets of steam, and the formation of a droplet of water begins , which grows until it becomes visible. (Later, in 1911, Wilson himself used this discovery, creating his famous device - the Wilson chamber). Thomson took advantage of his student's discovery in this way. Let us assume that in an ionized gas there is a certain number of ions that have the same charge, and these ions move with a known speed. The rapid expansion of the gas leads to its supersaturation, and each ion becomes a center of condensation. The current strength is equal to the product of the number of ions and the charge of each ion and its speed. The strength of the current can be measured, the speed of movement of the ions can also be measured, and if you somehow determine the number of particles, then you can find the charge of one particle. To do this, firstly, the mass of condensed water vapor was measured, and secondly, the mass of a single droplet. The latter was located as follows. The fall of droplets in the air was considered. The speed of this fall under the influence of gravity is equal, according to the Stokes formula,

– coefficient of viscosity of the medium in which the drop falls, i.e. air. Knowing this speed, you can find the radius of the droplet r and its volume, assuming the droplet is spherical. Multiplying this volume by the density of water, we find the mass of one droplet. Dividing the total mass of the condensed liquid by the mass of one droplet, we find their number, which is equal to the number of gas ions through which the charge of one ion is located. As an average of a large number of measurements, Thomson obtained for the desired charge a value of 6.5 10 –10 units. SGSM, which was in quite satisfactory agreement with the charge of the hydrogen ion already known at that time.

The method discussed above was improved by Wilson in 1899. Above the negatively charged droplet was a positively charged plate, which, with its attraction, balanced the force of gravity acting on the droplet. From this condition it was possible to find the charge of the condensation nucleus. A relevant question is: is the charge of the drop actually the charge of the electron? Isn't this the charge of ionized molecules, which does not have to be a priori equal to the charge of the electron? Thomson showed that the charge of an ionized molecule is indeed equal to the charge of an electron, appears regardless of the method of ionization of the substance, and always turns out to be equal to the charge of a monovalent ion during electrolysis. By substituting the value of this charge into the expression for the specific charge of the electron, we can find the mass of the latter. This mass turns out to be approximately 1800 times less than the mass of the hydrogen ion. Currently, the following values of fundamental constants are accepted: the electron charge is 1.601 10 –19 C; the mass of the electron is 9.08 10 –28 g, which is approximately 1840 times less than the mass of the hydrogen atom.

In connection with Thomson's research into the properties and nature of cathode rays, I would also like to mention his contribution to the study of the nature of the photoelectric effect. At that time, there was no clarity in the mechanism of this phenomenon - neither in the works of A.G. Stoletov (who died in May 1896, i.e. before the discovery of the electron), nor in the works of European physicists - the Italian A. Riga, the German V. Galvax, and even more so in the studies of G. Hertz, who died back in 1894. Thomson in 1899, studying the photoelectric effect using an experimental technique similar to the technique for studying the properties of cathode rays, established the following. If we assume that the electric current arising during the photoelectric effect is a flow of negatively charged particles, then we can theoretically calculate the movement of the particle that forms this current, simultaneously acting on it with electric and magnetic fields. Thomson's experiments confirmed that the current between two oppositely charged plates when the cathode is illuminated with ultraviolet rays is a flow of negatively charged particles. Measurements of the charge of these particles, carried out using the same method by which Thomson had previously measured the charge of ions, gave an average charge value that was close in order of magnitude to the charge value of the particles forming cathode rays. From here Thomson concluded that in both cases we should talk about particles of the same nature, i.e. about electrons.

Thomson's atom. The problem of “linking” open electrons with the structure of matter was posed by Thomson already in his work on determining the specific charge of electrons. The first model of the atom, proposed by Thomson, was based on the experiments of A. Mayer (USA) with floating magnets, which were carried out back in the late 70s. XIX century These experiments consisted of the following. In a vessel with water there were corks floating, into which magnetized needles were inserted, slightly protruding from them. The polarity of the visible ends of the needles was the same on all stoppers. Above these plugs, at a height of about 60 cm, a cylindrical magnet was located with the opposite pole, and the needles were attracted to the magnet, while simultaneously repelling each other. As a result, these plugs spontaneously formed various equilibrium geometric configurations. If there were 3 or 4 traffic jams, then they were located at the vertices of a regular polygon. If there were 6 of them, then 5 plugs floated at the vertices of the polygon, and the sixth was in the center. If there were, for example, 29, then one plug was again in the center of the figure, and the rest were located around it in rings: 6 floated in the ring closest to the center, 10 and 12, respectively, in the next rings as they moved away from the center. Thomson transferred the mechanical design to the structure of the atom, seeing in it the possibility of explaining the patterns inherent in the Periodic Table of D.I. Mendeleev (meaning the layer-by-layer distribution of electrons in the atom). However, in this case, the question of the specific number of electrons in the atom remained open. And if we assume that there are, for example, several hundred electrons (especially taking into account the fact that the mass of an electron is negligible compared to the mass of a hydrogen ion), then studying the behavior of electrons in such a structure is practically impossible. Therefore, already in 1899, Thomson modified his model, suggesting that the neutral atom contains a large number of electrons, the negative charge of which is compensated by “something which makes the space in which the electrons are scattered capable of acting as if it had a positive electric charge equal to the sum of the negative charges of electrons."

A few years later in the magazine " Philosophical Magazine" (No. 2, 1902) appeared the work of another Thomson - William, known as Lord Kelvin - which considered the interaction of an electron with an atom. Kelvin argued that an outer electron is attracted to an atom with a force inversely proportional to the square of the distance from the center of the electron to the center of the atom; an electron that is part of an atom is attracted to the latter with a force directly proportional to the distance from the center of the electron to the center of the atom. This shows, in particular, that Kelvin considers electrons not only as independent particles, but also as an integral part of the atom. This conclusion “is tantamount to the assumption of a uniform distribution of positive electricity in the space occupied by an atom of ordinary matter. From this it followed that there are two types of electricity: negative, granular, and positive, in the form of a continuous cloud, as “fluids” and, in particular, ether were usually imagined.” In general, we can say that, according to Kelvin, an atom has a uniform spherical distribution of positive electric charge and a certain number of electrons. If we are talking about a one-electron atom, then the electron must be at the center of the atom, surrounded by a cloud of positive charge. If there are two or more electrons in an atom, then the question arises about the stability of such an atom. Kelvin suggested that electrons appear to revolve around the center of the atom, being located on spherical surfaces concentric to the boundary of the atom, and these surfaces are also located inside the atom. But in this case, problems arise: when a charged particle moves, a magnetic field must arise, and when it moves with acceleration (and a rotating electron inevitably has centripetal acceleration), electromagnetic radiation must occur. Thomson studied these issues, remaining for about fifteen years a supporter of Kelvin's ideas.

Already in 1903, Thomson established that rotating electrons should generate elliptically polarized light waves. As for the magnetic field of rotating charges, then, as the theory shows, when electrons rotate under the influence of a force proportional to the distance from the charge to the center of rotation, the magnetic properties of matter can be explained only under the condition of energy dissipation. To the question of whether such scattering really exists, Thomson did not give a clear answer (apparently realizing that the presence of such scattering would raise the problem of the stability of the atom’s structure).

In 1904, Thomson considered the problem of mechanical stability of atomic structure. Despite the fact that now this approach is perceived as an anachronism (the behavior of the particles forming an atom should be considered from the standpoint of quantum mechanics rather than classical mechanics, about which absolutely nothing was known at that time), the results obtained by Thomson still have meaning to stop.

Firstly, Thomson established that electrons in an atom must rotate rapidly and the speed of this rotation cannot be less than a certain limit. Secondly, if the number of electrons in an atom is more than eight, then the electrons should be arranged in several rings, and the number of electrons in each ring should increase with increasing radius of the ring. Thirdly, for radioactive atoms, the speed of electrons due to radioactive radiation should gradually decrease, and at a certain limit of the decrease, “explosions” should occur, leading to the formation of a new atomic structure.

Nowadays, Rutherford's planetary model, which appeared in 1910 and was subsequently improved from a quantum perspective by N. Bohr, is generally accepted. Nevertheless, Thomson’s model is valuable in terms of posing: 1) the problem of connecting the number of electrons and their distribution with the mass of the atom; 2) problems of the nature and distribution of positive charge in the atom, compensating for the total negative electronic charge; 3) problems of atomic mass distribution. These problems were solved during the subsequent development of physics in the twentieth century, and their solution ultimately led to modern ideas about the structure of the atom.

Experimental proof of the existence of isotopes. The very idea that atoms of the same chemical element can have different atomic masses arose long before Thomson began to study the “isotope problem.” This idea in the 19th century. was expressed by the founder of organic chemistry A.M. Butlerov (1882) and somewhat later by W. Crooks (1886). The first radioactive isotopes were obtained in 1906 by the American chemist and at the same time physicist B. Boltwood (1870–1927) - two isotopes of thorium with different half-lives. The term “isotope” itself was introduced somewhat later by F. Soddy (1877–1956) after he formulated the displacement rules for radioactive decay. As for Thomson, in 1912 he experimentally studied the properties and features of the so-called channel rays, and a few words should be said about what it is.

We are talking about a flow of positive ions moving in a rarefied gas under the influence of an electric field. When electrons collide with gas molecules at the cathode in the region of the glow discharge and the cathode potential drop, the molecules are split into electrons and positive ions. These ions, accelerated by the electric field, come to the cathode at high speed. If the cathode has holes in the direction of ion movement, or if the cathode itself has the shape of a grid, then some of the ions, having passed through these channels, will end up in the post-cathode space. He began studying the behavior of such ions back in the 80s. XIX century previously mentioned E. Goldstein. Thomson, in 1912, studied the effect on channel rays (specifically for neon ions) of simultaneous electric and magnetic fields using the technique already mentioned (meaning Thomson’s “parabola method”). The beam of neon ions in his experiments was divided into two parabolic streams: a bright one, corresponding to atomic mass 20, and a weaker one, corresponding to atomic mass 22. From this, Thomson concluded that the neon contained in the Earth’s atmosphere is a mixture of two different gases. F. Soddy assessed the results of Thomson's research as follows: “This discovery represents the most unexpected application of what was found for one end of the Periodic Table to an element at the other end of the system; it confirms the assumption that the structure of matter in general is much more complex than is reflected in the periodic law alone.” The result was of great importance not only for atomic physics, but also for the subsequent development of experimental physics, because it indicated methods for measuring the masses of various isotopes.

In 1919, Thomson's student and assistant Francis William Aston (1877–1945) built the first mass spectrograph, with the help of which he experimentally proved the presence of isotopes in chlorine and mercury. The mass spectrograph uses exactly the Thomson method of deflecting charged particles under the influence of two fields, electric and magnetic, but Aston’s device used photography of separated flows of ions with different atomic masses, and in addition, the deflection of a charged particle in electric and magnetic fields was used - in one and the same plane, but in opposite directions. The physics of the mass spectrograph is mainly as follows. “Ions of the substance under study, first passing through an electric and then a magnetic field, fall on a photographic plate and leave a mark on it. Ion rejection depends on the ratio e/m, the same for all ions (or, better said, from ne/m, because an ion can carry more than one elementary charge). Therefore, all ions of the same mass are concentrated at the same point on the photographic plate, and ions of a different mass are concentrated at other points, so that by the point at which the ion hits the plate, its mass can be determined.”

In conclusion, a few words about the scientific school created by Thomson. His students are such prominent physicists of the twentieth century as P. Langevin, E. Rutherford, F. Aston, Charles Wilson. The last three, like Thomson himself, were awarded Nobel Prizes in physics in different years. Let's make special mention of his son. Father Thomson experimentally proved the very fact of the existence of the electron, and his son, George Paget Thomson, was awarded the Nobel Prize in 1937 for experimental proof of the wave nature of electrons (1927; in the same year, independently of Thomson Jr., similar research was carried out by K. Davisson together with his collaborator L. Germer (both were physicists from the USA; Davisson was also awarded the Nobel Prize). Here is how Erwin Schrödinger assessed these studies in 1928: “Some researchers (Davisson and Germer and the young J.P. Thomson) began to carry out an experiment for which a few years ago they would have been placed in a psychiatric hospital to monitor their state of mind . But they were completely successful."

After 1912, marked by experimental proof of the existence of isotopes, Thomson lived for another twenty-eight years. In 1918, he left the post of director of the Cavendish Laboratory (his place was taken by Rutherford) and then, until the end of his days, he headed the very Trinity College from where his path to science once began. Joseph John Thomson died at the age of 84 on August 30, 1940 and was buried in West Minster Abbey - the same place where Isaac Newton, Ernest Rutherford, and among the figures of English literature - Charles Dickens found their eternal rest.

Literature

1. Life of science. Ed. Kapitsa S.P. – M.: Nauka, 1973.

2. Kapitsa P.L. Experiment. Theory. Practice. – M.: Nauka, 1981.

3. Dorfman Ya.G. World history of physics from the beginning of the 19th to the mid-20th centuries. – M.: Nauka, 1979.

4. Liozzi M. History of physics. – M.: Mir, 1970.

The debate about who discovered the electron continues to this day. In addition to Joseph Thomson, some historians of science see Hendrik Lorentz and Peter Zeeman as the discoverer of the elementary particle, others - Emil Wichert, and still others - Philip Lenard. So who is he - the scientist who discovered the electron?

Atom means indivisible

The concept of "atom" was introduced into use by philosophers. The ancient Greek thinker Leucippus back in the 5th century BC. e. suggested that everything in the world consists of tiny particles. His student, Democritus, called them atoms. According to the philosopher, atoms are the “building blocks” of the universe, indivisible and eternal. The properties of substances depend on their shape and external structure: atoms of flowing water are smooth, metal atoms have profile teeth that impart hardness to the body.

The outstanding Russian scientist M.V. Lomonosov, the founder of the atomic-molecular theory, believed that in the composition of simple substances, corpuscles (molecules) are formed by one type of atom, while complex ones are formed by different types.

A self-taught chemist (Manchester) in 1803, relying on experimental data and taking the mass of hydrogen atoms as a conventional unit, established the relative atomic masses of some elements. The Englishman's atomic theory was of great importance for the further development of chemistry and physics.

By the beginning of the 20th century, a whole series of experimental data had been accumulated, proving the complexity of the structure of the atom. This includes the phenomenon of the photoelectric effect (G. Hertz, A. Stoletov 1887), the discovery of cathode (J. Plücker, W. Crooks, 1870) and x-rays (V. Roentgen, 1895) rays, radioactivity (A. Becquerel, 1896).

Scientists who worked with cathode rays were divided into two camps: some assumed the wave nature of the phenomenon, others - the corpuscular nature. Tangible results were achieved by Jean Baptiste Perin, a professor at the Ecole Normale Supérieure (Lille, France). In 1895, he showed through experiments that cathode rays are a stream of negatively charged particles. Maybe Peren is the physicist who discovered the electron?

On the threshold of great achievements

Physicist and mathematician George Stoney (Royal Irish University, Dublin) in 1874 voiced the assumption that electricity is discrete. In what year and who was he? In the course of experimental work on electrolysis, it was D. Stoney who determined the value of the minimum electric charge (although the result obtained (10 -20 C) was 16 times less than the actual one). In 1891, an Irish scientist named the unit of elementary electric charge “electron” (from the ancient Greek “amber”).

A year later, Hendrik Lawrence Netherlands) formulated the main provisions of his electronic theory, according to which the structure of any substance is based on discrete electrical charges. These scientists are not considered the discoverer of the particle, but their theoretical and practical research became a reliable foundation for Thomson's future discovery.

Unwavering Enthusiast

To the question of who discovered the electron and when, encyclopedias give a clear and unambiguous answer - Joseph John Thomson in 1897. So what is the merit of the English physicist?

The father of the future president of the Royal Society of London was a bookseller and from childhood instilled in his son a love of the printed word and a thirst for new knowledge. After graduating from Owens College (from 1903 - and the University of Cambridge in 1880), the young mathematician Joseph Thomson went to work at the Cavendish Laboratory. Experimental research completely fascinated the young scientist. Colleagues noted his tirelessness, determination and extraordinary passion for practical work.

In 1884, at the age of 28, Thomson was appointed director of the laboratory, succeeding Lord C. Rayleigh. Under Thomson's leadership, the laboratory over the next 35 years grew into one of the largest centers of world physics. N. Bor and P. Langevin began their journey from here.

Attention to detail

Thomson began his work on the study of cathode rays by checking the experiments of his predecessors. For many experiments, special equipment was made according to the personal drawings of the laboratory director. Having received qualitative confirmation of the experiments, Thomson did not even think of stopping there. He saw his main task as an accurate quantitative determination of the nature of the rays and their constituent particles.

The new tube, designed for the following experiments, included not only the usual cathode and accelerating electrodes (in the form of plates and rings) with deflecting voltage. The stream of corpuscles was directed onto a screen covered with a thin layer of a substance that glowed when the particles struck. The flow was supposed to be controlled by the combined influence of electric and magnetic fields.

Components of an atom

It's hard to be a pioneer. It is even more difficult to defend your beliefs, which run counter to the concepts that have been established for thousands of years. Believing in himself and in his team made Thomson the person who discovered the electron.

The experience produced stunning results. The mass of the particles turned out to be 2 thousand times less than that of hydrogen ions. The ratio of the charge of a corpuscle to its mass does not depend on the flow speed, the properties of the cathode material, or the nature of the gaseous medium in which the discharge occurs. A conclusion came to mind that contradicted all foundations: corpuscles are universal particles of matter within an atom. Time after time, Thomson diligently and carefully checked the results of experiments and calculations. When there was no longer any doubt, a report was made on the nature of cathode rays to the Royal Society of London. In the spring of 1897, the atom ceased to be indivisible. In 1906, Joseph Thomson was awarded the Nobel Prize in Physics.

Unknown Johann Wichert

The name of the geophysics teacher at Köningsbör and then the University of Göttingen, researcher of the seismography of our planet Johann Emil Wichert, is better known in the professional circles of geologists and geographers. But it is also familiar to physicists. This is the only person whom official science, along with Thomson, recognizes as the discoverer of the electron. And to be absolutely precise, the work describing Wichert’s experiments and calculations was published in January 1897 - four months earlier than the Englishman’s report. Who discovered the electron has already been historically decided, but the fact remains a fact.

For reference: Thomson did not use the term “electron” in any of his works. He used the name "corpuscles".

Who discovered the proton, neutron and electron?

After the discovery of the first elementary particle, assumptions began to be made about the possible structure of the atom. One of the first models was proposed by Thomson himself. An atom, he said, is like a piece of raisin pudding: a positively charged body interspersed with negative particles.

In 1911 (New Zealand, Great Britain) he suggested that the atomic model has a planetary structure. Two years later, he hypothesized the existence of a positively charged particle in the nucleus of an atom and, having obtained it experimentally, called it a proton. He also predicted the presence in the nucleus of a neutral particle with the mass of a proton (the neutron was discovered in 1932 by the English scientist J. Chadwick). In 1918, Joseph Thomson transferred control of the laboratory to Ernest Rutherford.

Needless to say, the discovery of the electron allowed us to take a new look at the electrical, magnetic and optical properties of matter. It is difficult to overestimate the role of Thomson and his followers in the development of atomic and nuclear physics.

An electron is a subatomic particle that responds to both electric and magnetic fields.

Throughout the second half of the 19th century, physicists actively studied the phenomenon of cathode rays. The simplest apparatus in which they were observed was a sealed glass tube filled with rarefied gas, into which an electrode was soldered on both sides: on one side cathode, connected to the negative pole of the electric battery; with another - anode, connected to the positive pole. When high voltage was applied to the cathode-anode pair, the rarefied gas in the tube began to glow, and at low voltages the glow was observed only in the cathode region, and with increasing voltage - inside the entire tube; however, when the gas was pumped out of the tube, starting from a certain moment, the glow disappeared in the cathode region, remaining near the anode. Scientists attributed this glow cathode rays.

Using a new tube design, Thomson consistently showed that:

cathode rays are deflected in a magnetic field in the absence of an electric one;
cathode rays are deflected in an electric field in the absence of a magnetic field;
with the simultaneous action of electric and magnetic fields of balanced intensity, oriented in directions that separately cause deviations in opposite directions, the cathode rays propagate rectilinearly, that is, the action of the two fields is mutually balanced.

Thomson found that the relationship between the electric and magnetic fields at which their effects are balanced depends on the speed at which the particles move. After conducting a series of measurements, Thomson was able to determine the speed of movement of the cathode rays. It turned out that they move much slower than the speed of light, which meant that cathode rays could only be particles, since any electromagnetic radiation, including light itself, travels at the speed of light (see Spectrum of electromagnetic radiation). These unknown particles. Thomson called them “corpuscles,” but they soon became known as “electrons.”

It immediately became clear that electrons must exist as part of atoms - otherwise, where would they come from? April 30, 1897 - the date of Thomson's report of his results at a meeting of the Royal Society of London - is considered the birthday of the electron. And on this day the idea of the “indivisibility” of atoms became a thing of the past (see Atomic theory of the structure of matter). Together with the discovery of the atomic nucleus that followed a little over ten years later (see Rutherford's experiment), the discovery of the electron laid the foundation for the modern model of the atom.

History of the discovery of the electron. In what year and by whom was the electron discovered? The physicist who discovered the electron: name, history of discovery and interesting facts Which scientist discovered the electron

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