J. J. Thomson

J. J. Thomson was an English physicist who discovered the electron and measured its charge-to-mass ratio. His work showed that atoms contain smaller particles.

Ernest Rutherford: A physicist who pioneered nuclear physics and succeeded Thomson as director of the Cavendish Laboratory. Rutherford studied under Thomson before overturning Thomson’s model of the atom.
Cathode ray: A stream of electrons emitted from a cathode in a low-pressure tube. Thomson treated cathode rays as particles and measured how electric and magnetic fields deflected them.
William Crookes: An English chemist and physicist who studied cathode rays using evacuated discharge tubes. Crookes’s tube experiments supplied the apparatus and observations Thomson reinterpreted as evidence for particles.
Rutherford model: An atomic model with a tiny, positively charged nucleus surrounded by electrons. Rutherford’s model replaced Thomson’s diffuse positive sphere after alpha-particle scattering revealed a nucleus.
John Townsend: An Irish physicist who studied electrical conduction in gases and worked at the Cavendish Laboratory. Townsend was among Thomson’s students investigating ions and electrical phenomena in gases.
Cathode-ray tube: A vacuum tube in which electrons emitted by a cathode form a beam that strikes a screen or target. Its controlled beams let Thomson test whether cathode rays carried electric charge.
Eugen Goldstein: A German physicist who studied gas-discharge tubes and named cathode rays. Goldstein’s work on electrical discharges helped establish the experimental problem Thomson addressed.
Isotope: One of two or more atoms of the same element with different numbers of neutrons. Thomson’s positive-ray work revealed neon atoms with different masses, helping establish isotopes.
Charles Thomson Rees Wilson: A Scottish physicist who developed the cloud chamber, a device for visualizing charged particles. Wilson worked in Thomson’s laboratory and built instruments for studying ionized air.
Charge-to-mass ratio: The electric charge of a particle divided by its mass. Thomson measured this ratio for cathode-ray particles, showing they were far lighter than atoms.

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