The discovery of electrons by Joseph John Thomson

Joseph John Thomson was born in Manchester. Here, in Manchester, he graduated from Owenscollidge, and in 1876-1880 he studied at the University of Cambridge at the famous college of the Holy Trinity (Trinity College). In January 1880, Thomson successfully passed the final exams and began working at the Cavendish Laboratory.

His first article, published in 1880, was devoted to the electromagnetic theory of light . The following year, two papers appeared, one of which laid the foundation for the electromagnetic theory of mass.

Thomson was obsessed with experimental physics. Obsessed in the best sense of the word. The scientific achievements of Thomson were highly appreciated by the director of the laboratory, Cavendish Rayleigh . Leaving in 1884 as director, he did not hesitate to recommend Thomson as his successor.

From 1884 to 1919, Thomson directed the laboratory of Cavendish. During this time, it has become a major center of world physics, an international school of physicists. Here began their scientific path Rutherford, Bohr, Langevin and many others, including Russian scientists .

Thomson's research program was broad: questions of the passage of an electric current through gases, the electronic theory of metals, the study of the nature of various kinds of rays ...

Taking up the investigation of the cathode rays, Thomson first of all decided to check whether the experiments of his predecessors, who had achieved the deviation of the rays by electric fields, were thoroughly set. He plans a second experiment, constructs special equipment for him, monitors the care of the order, and the expected result is obvious.

In the tube, designed by Thomson, the cathode rays obediently attracted to the positively charged plate and were clearly repelled from the negative. That is, they behaved the way the flow of tiny corpuscles charged with negative electricity was supposed to flow. Excellent result!

Certainly, he could put an end to all disputes about the nature of cathode rays. But Thomson did not consider his study complete. Having determined the nature of the rays qualitatively, he wanted to give an accurate quantitative definition of the constituent corpuscles.

Inspired by his first success, he designed a new tube: a cathode, accelerating electrodes in the form of rings and plates, which could be fed with a deflecting voltage. On the wall opposite to the cathode, he applied a thin layer of a substance capable of glowing under the impact of incident particles. An ancestor of electron-beam tubes, so familiar to us in the age of TVs and radars, turned out.

The purpose of the Thomson experiment was to deflect the beam of corpuscles by an electric field and to compensate for this deviation by the magnetic field. The conclusions to which he came as a result of the experiment were astonishing. First, it turned out that the particles are flying in a tube with huge velocities close to light ones. And secondly, the electric charge per unit mass of corpuscles was fantastically large.

What kind of particles were they: unknown atoms carrying huge electrical charges, or tiny particles with an insignificant mass, but also with a smaller charge? He further discovered that the ratio of the specific charge to the unit mass is a constant value, independent of the velocity of the particles, not of the cathode material, nor of the nature of the gas in which the discharge occurs.

Such independence was alarming. It seems that the corpuscles were some kind of universal particles of matter, constituent parts of atoms. "After a long discussion of experiments," Thompson writes in his memoirs, "it turned out that I can not avoid the following conclusions:

1. That atoms are not indivisible, since they can be pulled out of negatively charged particles under the action of electric forces, impact of rapidly moving particles, ultraviolet light or heat.

2. That these particles are all of the same mass, carry the same charge of negative electricity, from whatever kind of atoms they occur, and are components of all atoms.

3. The mass of these particles is less than one thousandth of the mass of the hydrogen atom. I first called these particles corpuscles, but they are now called the more suitable name "electron".

Thomson set to work. First of all, it was necessary to determine the parameters of the mysterious corpuscles, and then, perhaps, it will be possible to decide what they are. The results of the calculations showed: there is no doubt, unknown particles are nothing else than minute electrical charges - indivisible atoms of electricity, or electrons.

April 29, 1897 in a room where for more than two hundred years, there were meetings of the Royal Society of London, held his report. The audience was delighted. The enthusiasm of those present was not due to the fact that colleague JJ Thomson so convincingly revealed the true nature of the cathode rays.

The situation was much more serious. Atoms, the very first bricks of matter, ceased to be elementary round grains, impenetrable and indivisible, particles without any internal structure ...

If negative corpuscles could fly out of them, it means that atoms must have been some kind of complex system, a system consisting of something charged with positive electricity and negatively charged corpuscles - electrons. Now the further, the most necessary directions of future searches became visible.

First of all, of course, it was necessary to determine exactly the charge and mass of one electron. This would make it possible to clarify the masses of the atoms of all elements, calculate the masses of molecules, and give recommendations for the correct formulation of reactions.

In 1903, in the same Cavendish laboratory at Thomson, G. Wilson made an important change in Thomson's method. In a vessel in which a rapid adiabatic expansion of the ionized air is carried out, condenser plates are placed between which an electric field can be created and the fall of the cloud, both in the presence of a field and in its absence, can be observed.

Wilson's measurements gave a value for the electron charge as 3.1 times 10 per minus the tenth power of abs. Units Wilson's method was used by many researchers, including students of Petersburg University Malikov and Alekseev , who found a charge equal to 4.5 multiplied by 10 to minus the tenth degree of abs. Units This was the most close to the true meaning of the result from all the results obtained before Milliken began in 1909 measurements with individual drops.

Thus, an electron was discovered and measured , a universal particle of atoms , the first of the so-called "elementary particles" discovered by physicists. This discovery made it possible for physicists, first of all, to raise the question of studying the electric, magnetic, and optical properties of matter in a new way.

Source of the information: Samin D.K. "One hundred great scientific discoveries.", M.: "Veche", 2002.