Chemistry / Unit 2 Chem 0193 short lesson, about 20 seconds
J. J. Thomson and the Discovery of the Electron (1897)
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The idea
In 1897, J. J. Thomson used a cathode ray tube to show cathode rays were negatively charged particles lighter than any atom.
In practice
Deflecting the ray with electric and magnetic fields let Thomson calculate a charge-to-mass ratio, identical no matter which metal formed electrodes.
Where people slip
The particle was not a smaller atom; being far lighter than any atom marked it a new subatomic constituent.
Your place on the trail
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