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British physicist Joseph John Thomson was a mathematician by education and a doyen of experimental physics. He is the man credited for the discovery of electrons and proving to the world that an atom is not the most fundamental particle and can be further divided into sub-atomic particles. His path-breaking contributions in the field of Electromagnetism, atomic structure and charge- mass ratio is still revered by scientists since they paved the way for further research in the field of electronics, atomic physics, nano physics and radioactivity. He was awarded the Nobel Prize for Physics in 1906 for his study of conductivity in different gases. He was knighted in the year 1908.
Life Journey
Joseph John Thomson was born on December 18, 1856 in Cheetam Hill, north of Manchester, England. His father was a bookseller and wanted him to become an engineer, but destiny had other ideas. ’J J’, as he was fondly called by his peers, lost his father at a young age of sixteen when he was studying Mathematics at Owens College. At the age of 20, he joined Trinity College, Cambridge University, to study Mathematics on a scholarship. He graduated in 1890 with a Second Wrangler, an honor for standing second in the class.
J J Thomson was associated with Cambridge University in various capacities. After graduation, he became a fellow at Trinity and worked at Cavendish Laboratory, a unit of the Cambridge Physics department. In 1884, he was appointed Cavendish Professor of Experimental Physics, succeeding Lord Rayleigh, a position he held till 1918. The year of 1884 also saw Thomson elected as a Fellow to Royal Society of London. Cambridge remained his lifelong address until he passed away on August 30, 1940.
Scientific Works
J J Thompson has a huge body of scientific works to his credit. Here we will talk about three of his most important contributions.
Discovery of the Electron (1897)
Thomson conducted a series of experiments to study the nature of electric discharge in a high vacuum cathode ray tube. He analyzed the deflection of cathode rays in an electric field between two alternately charged aluminum plates. He repeated the same experiment in a magnetic field. He observed that cathode rays deflected towards positive plates and away from negative fields. He concluded that cathode rays carry a negatively charged particle and named it Corpuscle. This corpuscle is what is known today as an electron, and so his research formed the base of research in the field of electronics. He also deduced that these particles are within the atom and have a very large charge to mass ratio. Later, he went on to calculate the value of this charge itself.
Plum Pudding Model of Atom (1904)
Thomson was the pioneer to have suggested that the atom is not the most basic unit of matter but an entity that can be further divided into sub-atomic matter. He described the electron as, “This matter being the substance from which all chemical elements are derived”. He proposed the Plum Pudding model of the atom as a sphere of positive matter in which electrons are positioned by electrostatic forces. He tried to calculate the number of electrons in an atom by measuring the scattering of light, beta, gamma and X rays. This formed the base for his student Earnest Rutherford’s research.
Development of Mass Spectrograph
Thomson’s last major experiment focused on determining the nature of positively charged particles and led to the development of Mass Spectrograph. Another of his students, Francis Aston, improved on this instrument and went on to discover isotopes in non-radioactive elements.
Thomson is not only remembered for his own contributions to Physics but also as a gifted lecturer and teacher. He inspired and mentored a generation of scientists. Seven of his students were awarded Nobel Prizes, including his son, Sir George Paget Thomson.
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