J.J. Thomson - English Physicist
(1856-1940)
1897
While director of the Cavendish Lab at Cambridge, Thomson reports the discovery of a negatively charged constituent of all atoms. He names these particles electrons after a name proposed in 1894 by G.J. Stoney.
Thomson used a gas discharge tube and external magnetic and electric fields to discover the electron. When just the external magnetic field was applied, the cathode rays in the tube were deflected a certain amount. When just the external electric field was applied, the cathode rays were deflected in the opposite direction. Both deflections indicated that the cathode rays possesed a negative charge. Finally, when both the external magnetic and electric fields were applied, Thomson could adjust their strengths so that their effects cancelled each other. In this way, Thomson discovered the charge to mass ratio of the electron.
Cathode ray tube and applied external magnetic field.
Cathode ray tube and applied external electric field.
Cathode ray tube with both fields applied.
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