GREAT SCIENTISTS OF WORLD - JOSEPH JOHN THOMSON

Sir  Joseph John Thomson, (born December 18, 1856, Cheetham Hill, near Manchester, England—died August 30, 1940, Cambridge, Cambridgeshire), English physicist who helped revolutionize the knowledge of atomic structure by his discovery of the electron (1897.

 Joseph John (J. J.) Thomson performed a series of experiments in 1897 designed to study the nature of electric discharge in a high-vacuum cathode-ray tube, an area being investigated by many scientists at the time.

In 1897, he showed that cathode rays were composed of very small negatively charged particles. These particles later were named electrons. The apparatus of his experiment is called the cathode-ray tube (CRT). J. J.

 J. J. Thomson

  took science to new heights with his 1897 discovery of the electron – the first subatomic particle. This discovery upended the prevailing theory that the atom was the smallest fundamental unit. He also found the first evidence that stable elements can exist as isotopes and invented one of the most powerful tools in analytical chemistry – the mass spectrometer.

 

 In 1906, Thomson began studying positively charged ions, or positive rays. This led to one of his other famous discoveries in 1912 when he channeled a stream of ionized neon through a magnetic and an electric field and used deflection techniques to measure the charge to mass ratio. In doing so, he discovered that neon was composed of two different kinds of atoms, and proved the existence of isotopes in a stable element. This was the first use of mass spectrometry.

 

 

Thomson's experiments with cathode ray tubes showed that all atoms contain tiny negatively charged subatomic particles or electrons. Thomson's plum pudding model of the atom had negatively-charged electrons embedded within a positively-charged "soup."

 

 

 Thomson performed experiments to show that atoms consisted of sub atomic particles that had positive and negative charges. He determined that the negatively charged particles (electrons) were much lighter than the positively charged particles.

 

 

 

 We can never see the subatomic particles directly, but can only infer from observation of such indirect effects like tracks. If there are many of them and they are emitting some radiation, and also if we shine some radiation on then and receive back the response this will also constitute a kind of seeing.

 

Experiments with beams of negative particles were performed in  by  Thomson, and led to his conclusion  that they consisted of lightweight particles with a negative electric charge, nowadays known as electrons.

 The Nobel Prize in Physics 1906 was awarded to Joseph  Thomson "in recognition of the great merits of his theoretical and experimental investigations on the conduction of electricity by gases."

 In his classic experiment, Thomson measured the mass-to-charge ratio of the cathode rays by measuring how much they were deflected by a magnetic field and comparing this with the electric deflection. Significantly, the rays from every cathode yielded the same mass-to-charge ratio.

 To a large extent, it was Thomson who made atomic physics a modern science. The studies of nuclear organization that continue even to this day and the further identification of elementary particles all followed his most outstanding accomplishment, his discovery of the electron in 1897.

 Thomson married Rose Paget, one of his students, in 1890. They had one daughter, Joan, and one son, George Paget Thomson, who went on to become a physicist and win a Nobel Prize of his own. J.J. Thomson published 13 books and more than 200 papers in his lifetime. In addition to being awarded the Nobel Prize in 1906.

 

 

 In addition to being awarded the Nobel Prize in 1906, he was knighted in 1908 by King Edward VII. He left research in 1918 to become Master of Trinity College. He died in Cambridge on August 30, 1940, and is buried in Westminster Abbey near two other influential scientists: Isaac Newton and Charles Darwin.

J.J THOMSON