JJ THOMPSON – Experimental Physicist Nonpareil

Between 1884 and 1919 an earnest looking Professor along with a bunch of talented research students in a rather underfunded Cavendish laboratory in Cambridge split the atom and started a new branch of science known as particle Physics. The Professor was JJ Thomson, the discoverer of electron for which he got the Nobel Prize in 1906. What followed subsequently was not anticipated – seven of JI’s research students went on to win the Nobel Prize in Physics and Chemistry, a feat unrivalled by any other Professor. One would wonder what was happening at the Cavendish Laboratory under JJ that would secure such a roll of honour. Was it just a quirk of fate that some of the best minds in Physics congregated at Cavendish during the time or was it JI’s ability to make intelligent men do brilliant work. JJ Thomson is the only Professor who changed scientific history not just through individual brilliance, but through careful nurture of extraordinary minds.  As of 2019, 30 Cavendish Researchers had won Nobel Prizes. Notable discoveries to have occurred at the Cavendish Laboratory include the discovery of the electron, neutron, and structure of DNA:

The cathode ray tube is the basis of two omnipresent modern technologies: the television screen and the computer monitor. But originally, in the nineteenth century, the cathode ray tube was an experimental apparatus. In its basic form, it is a glass tube plugged by metal electrodes, with the air evacuated and some specific gas pumped in. When the electrodes are connected to a battery with enough voltage, the cathode rays strike the opposite end of the tube and glow or fluoresce. The rays are streams of electrons, not light rays. And they were the first subatomis particle to be discovered. The discovery of the electron, by joseph john Thomson in 1897, was the crucial first step in the development of the twentieth-century concept of the atom.

Joseph John Thomson was born on December 18, 1856, at Cheetham Hill, a suburb of Manchester, England. His father, Joseph Thomson, was a publisher and antiquarian book dealer of Scottish origin; his mother was Emma Swindells. The family atmosphere was parochial rather than learned, but James was precocious in school and had an exceptional memory. In 1870, at age fourteen, he began attending Owens College and came under the influence of Balfour Stewart, a physics professor. When his father died in 1873, Joseph received a scholarship which honored the memory of JOHN DALTON, the Manchesterian whose work first recast atomic theory in modern form. After graduating Trinity College in 1880 as the “second wrangler” in mathematics, Thomson was elected a fellow and remained at Cambridge for the rest of his life. He worked at Cavendish Laboratory, which had been opened in 1871 and originally headed by JAMES GLERK MAXWELL. In 1884, at an exceptionally young age, Thomson was named Cavendish Professor of Experimental Physics.

Toward the end of the nineteenth century, it became probable that atoms-whose existence was still doubted in some quarters-were not simply impenetrable balls of various weights, but comprised of some underlying structure. The evolving theory of electromagnetism implied that atoms were in some way electrical; and experiments hinted that, possibly, the glowing cathode rays were charged atomic particles. William Crookes, whose improved vacuum tubes were the basis of Thomson’s experiments, believed as early as the 1870s that the rays resembled a stream of molecules. Thomson benefited from a great deal of data, which he gathered and pored over for a number of years, as well as from a full theoretical grasp of electromagnetic theory. In addition, he was inspired by the discovery of X rays.

His decisive investigations took place from 1896 to 1898.

In the first of several crucial experiments, Thomson placed two metal plates, connected to a battery, inside a cathode tube, creating a magnetic field through which the rays would have to pass. When Thomson found that the presence of this field could deflect cathode rays, he could conclude that they consisted of particles and were not light beams. More significant, Thomson now had the means to derive from the velocity, which was known, the particles elm, that is, the ratio between the electric charge and the mass. When Thomson found a very large ratio between charge and mass, he inferred that the particle was very small- indeed, at least one thousand times smaller than hydrogen, the lightest known atom.

Thomson tested a variety of materials and gases and achieved for all essentially the same elm ratio. Continuing his experiments and using a cloud chamber, he was able in 1898 to verify the size of the “corpuscles.” His conclusion constitutes one of the true milestones in physics: Cathode rays consist of partides that are elementary and found in all matter. As he put it himself later: “[The] carriers of electricity are bodies… having a mass very much smaller than that of the atom of any known element, and are of the same character from whatever source the negative electricity may be derived.”

When Thomson first announced his preliminary discoveries on April 30 ,1897 at a Friday evening lecture of the Royal Institute, he was understood by only a few of his colleagues. But so convincing was his series of experiments that recognition was more or less immediate. ” The scientific world seemed suddenly to awaken to the fact that their conceptions had been revolutionized.

Thomason’s term for the elementary particle “corpuscle” was soon replaced by “electron” which had been proposed several years earlier by the Irish Physicist George Johnston Stoney.

In 1903 Thomson published a summary of his work, Conduction of electricity through gases. He developed a “plum pudding” model of the atom, in which in which electrons studded a uniform sphere. This soon gave way to the solar-system model developed by Ernest Rutherford and Neil’s Bohr. which became the last of the visualised prototypes. Today neither the atom nor the electrons can be effectively understood through visual representation.

Thomson was a much-beloved scientist and teacher. As stated earlier a number of his students went on to become Nobel laureates. The Cavendish Laboratory was already a mecca for physicists, and it remained so for a long time afterward. Thomson was highly ingenious at designing and refining instruments. “Thomson’s success,” wrote A. E. E.

McKenzie, “rested on his ability to perceive with clarity a fundamental problem, to formulate an hypothesis, to conceive experimental tests and to marshal a concerted attack from all angles by a team working under him.

In 1906 Thomson himself was awarded the Nobel Prize for physics. After 1912 he reduced his research load and concentrated on administrative duties. He was knighted in 1908: in 1918 he was named to the mastership of Trinity College, a high honor. He resigned from the Cavendish in 1919 and lived, largely in retirement, until his death on August 30, 1940. His remains were cremated and his funeral was held in Westminster Abbey, near the graves of ISAAC NEWTON CHARLES DARWIN and ERNEST RUTHERFORD.