Radiophysics. Халюшева Г.Р. - 40 стр.

         10 Unit 10

         10.1 Text 10
                                             A revolution in physical science – electronics

         In the closing year of the nineteenth century an absent–minded professor of Physics in Cambridge discovered the
electron. He was Joseph John Thomson, born in Manchester, first a student and then a lecturer in mathematics at Trinity
College, and in 1884 was appointed Professor of Physics when he was only twenty–eight years old. However little his
thoughts may have been concerned with everyday matters they were occupied to very good purpose in exploring the
mysterious phenomena associated with the conduction of electricity through gases.
       "I was led to investigations on this subject", he wrote, "by having come to the
conclusion that whenever a gas conducts electricity some of its molecules have been
split up and that it is the molecules which have been thus modified which impart
electrical conductivity to the gas...It was not until 1897 that I discovered that the
decomposition of the molecules was of quite a different type from ordinary atomic
dissociation; then I found that one of the bodies into which the molecules split up, the
one carrying the negative charge, is something totally different from an atom and is
indeed smaller in mass than one thousandth part of the smallest atom known."
          This characteristic statement illustrates the clarity and originality of Thomson's thinking and the extraordinary
insight into the invisible world of atoms which enabled him to identify and measure the incredibly small electron, and to
inspire his pupils and colleagues to discover the structure of the atom. It would be naive to imagine that the discovery of the
electron would have been long delayed if Thomson had been less brilliant. The time was ripe for it and in the main centres
of physical research of the nineteenth–century world other scientists were making experiments. His great achievement was
the peak of physical science in the nineteenth century and the source of its main stream in the twentieth. Thomson was a
remarkable man who saw further than most of his colleagues but not even he could have foreseen the profound effect his
discovery was to have on the lives of the people in the twentieth century.
          Before the discovery of the electron our knowledge of the nature of matter had advanced little beyond the
conjectures of the Ancient Greeks. There was very strong evidence that all substances were made up of a limited variety of
different kinds of "ultimate" particles called atoms. The word "atom" means "uncuttable" and it was generally accepted that
if it were possible to cut up a piece of, say, pure gold into smaller and smaller bits, the process would end with a large
number of very small, identical, gold atoms which
          could be cut no further. A great deal was known about the properties of substances like gold, copper and iron, yet
no one could explain the differences between gold, copper and iron atoms. The efforts of the alchemists, for example, to
change iron, copper or tin into gold simply underlined their ignorance of atomic structure. Today one can break up atoms
into smaller bits and change some kinds of atoms into other kinds because we know something of how atoms are made.
Modern atomic theory began with Thomson's discoveries in the Cavendish Laboratory and caused a revolution in physics
which in turn translated the whole of science.
          The searchlight which Thomson threw on the hidden world of the atom paved the way for many exciting new
discoveries at the Cavendish Laboratory and by physicists all over the world. The outstanding achievements alone included:
the discovery of the atomic nucleus and the proton by Rutherford, Thomson's young collaborator from New Zealand who
was to outshine even the illustrious "J.J." ; the discovery of the neutron by one of Rutherford's "young men", James
Chadwick; and the invention of the particle accelerator by two others, Cockcroft and Walton. Discoveries such as these
inspired the great mathematical physicists of the early twentieth century who were then formulating their revolutionary
theories.Planck's Quantum Theory, Einstein's Theory of Relativity. Bohr's model of the atom,were all concerned to account
for the observed behaviour of electrons,protons and other fundamental particles of the universe.
          The revolution in pure science rapidly bore fruit in many fields of electronics. The vacuum techniques developed
for the study of free electrons led directly to the radio valve, and the Crooke's tube which aroused Thomson's interest in
cathode rays was the father of the television receiver. The new electronics combined with the older techniques of the
telegraph and telephone produced a revolution in communications. If the discovery of electron had led only to radio and
television it would still represent a decisive factor in the shaping of our civilization – but it led to still wore discoveries of
Russian and foreign scientists.
          Electronics produced radar.It led to nucleonics and hence to the exploitation of the immense store of energy locked
in the atom. It gave birth to the electronic computer. By the middle of the twentieth century a rapidly expanding, world–