If you randomly ask 100 people to name at least three known elementary particles, then perhaps not everyone will name all three, but no one will forget to name the champion in popularity - the electron. The smallest, lightest among the particles carrying a charge, omnipresent and ..., unfortunately, "negative", it is part of any substance on Earth and this already deserves a special relation to itself. The name of the particle originated in ancient Greece from the Greek word “amber” - a material that the ancients loved for its ability to attract small objects. Then, when the study of electricity got a wider scope, the term "electron" began to mean indivisible, and hence the smallest unit of charge.
The eternal life of the electron, as an integral particle of matter, was presented by a group of physicists led by J.J. Thomson. In 1897, they, exploring the cathode rays, determined how the mass of an electron relates to its charge, and found that this ratio does not depend on the cathode material. The next step in understanding the nature of the electron was made by Becquerel in 1900. In his experiment, it was proved that beta rays of radium are also deflected in an electric field, and their mass-to-charge ratio is the same with cathode rays. This became an indisputable proof that the electron is an “independent piece” of the atom of any substance. And then, in 1909, Robert Milliken, in an experiment with droplets of oil that fell in an electric field, was able to measure the electric force balancing the force of gravity. Then the elementary value, i.e. smallest charge:
eo = - 1.602176487 (49) * 10-19 Cl.
This was enough to calculate the mass of the electron:
me = 9.10938215 (15) * 10-31kg.
It would seem that now the order, everything is behind, but this was only the beginning of a long way of knowing the nature of the electron.
For a long time, the dead end of physics was the two-faced essence of the electron, which was not yet proved, but more and more declaring itself: its quantum-mechanical properties pointed to a particle, and in the experiments on the interference of electron beams on parallel slits, the wave nature appeared. The moment of truth came in 1924, when at first Louis de Broglie endowed everything material, and the electron, too, with waves named after him, and after 3 years Pauli completed the formation of the initial concepts of quantum mechanics that describe the quantum nature of particles. Then came the turn of Erwin Schrödinger and Paul Dirac - complementing each other, they found equations to describe the essence of the electron, in which the electron mass and Planck's constant, quantum quantities, were reflected through wave characteristics - frequency and wavelength.
Of course, such duplicity of an elementary particle had far-reaching consequences. Over time, it became clear that the characteristics of a free electron outside a substance (cathode rays as an example) are not at all the same as for an electron in the form of an electric current in a crystal. For a free electron, its mass is known as the "rest mass of the electron." The physical nature of the difference in mass of an electron under different conditions follows from the fact that its energy depends on the saturation of the space in which it moves by the magnetic field . Deeper “showdowns” show that the magnitude of the magnetic field of electrons moving in a conductor, more precisely, the flow of current in a substance, depends not on the magnitude of the charge of the current carriers, but on their mass. But, on the other hand, the specific energy of the magnetic field is equal to the kinetic energy density of moving charges, and the growth of this energy is actually equivalent to the increased mass of charge carriers, which was called the "effective mass of the electron." It was analytically determined that it is a / 2λ times larger than the mass of a free electron, where a is the distance between the planes bounding the conductor, λ is the depth of the skin layer of the magnetic field.
In elementary particle physics, the mass of an electron is one of the reference constants. The biography of the electron has not ended - research is always relevant and in demand, where it acts as an indispensable participant. It has long been clear that although it is small, elementary, and the Universe without it is not a step away.