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J. J. Thomson

2007 Schools Wikipedia Selection. Related subjects: British History Post
1900; Engineers and inventors

   CAPTION: J.J. Thomson

   Sir Joseph John Thomson
   Sir Joseph John Thomson
         Born        18 December 1856
                     Cheetham Hill, Manchester, UK
         Died        30 August 1940
                     Cambridge, UK
       Residence     UK
      Nationality    English
         Field       Physicist
      Institution    University of Cambridge
                     Princeton University
                     Yale University
      Alma Mater     Owens College
                     University of Cambridge
   Doctoral Advisor  John Strutt (Rayleigh)
                     Edward John Routh
   Doctoral Students Charles T. R. Wilson
                     Ernest Rutherford
                     John Townsend
                     Owen Richardson
                     William Henry Bragg
       Known for     Plum pudding model
                     Discovery of electron
                     Discovery of isotopes
                     Invention of the mass spectrometer
    Notable Prizes   Nobel Prize for Physics (1906)
       Religion      Anglican
   Note that he is the father of George Paget Thomson.

   Sir Joseph John Thomson, OM, FRS ( 18 December 1856 – 30 August 1940)
   often known as J. J. Thomson, was an English physicist. Thomson is
   credited for the discovery of the electron, of isotopes and the
   invention of the mass spectrometer.

Biography

   Joseph John Thomson was born in 1856 in Cheetham Hill, Manchester in
   England, of Scottish parentage. He studied engineering at Owens
   College, Manchester, and moved on to Trinity College, Cambridge. In
   1880 he received his B.A. in mathematics. In 1884 he became Cavendish
   Professor of Physics. One of his students was Ernest Rutherford, who
   would later succeed him in the post. In 1890 he married Rose Elisabeth
   Paget, daughter of Sir George Edward Paget, KCB, a physician and then
   Regius Professor of Physic at Cambridge. He fathered one son, George
   Paget Thomson, and one daughter, Joan Paget Thomson, with her. His son
   became a noted physicist in his own right, winning the Nobel Prize
   himself for discovering the wave-like properties of electrons.

   For his discovery of the electron, he was awarded a Nobel Prize in
   1906. He was knighted in 1908 and appointed to the Order of Merit in
   1912. In 1914 he gave the Romanes Lecture in Oxford on "The atomic
   theory". In 1918 he became Master of Trinity College, Cambridge, where
   he remained until his death. He died in 1940 and was buried in
   Westminster Abbey, close to Sir Isaac Newton.

Work on cathode rays

   Thomson conducted a series of experiments with cathode ray tubes which
   led him to the discovery of electrons and subatomic particles.
   Thomson's first experiment.
   Enlarge
   Thomson's first experiment.

   In his first experiment, he investigated whether or not the negative
   charge could be separated from the cathode rays by means of magnetism.
   He constructed a cathode ray tube ending in a pair of cylinders with
   slits in them. These slits were in turn connected to an electrometer.
   Thomson found that if the rays were magnetically bent such that they
   could not enter the slit, the electrometer registered little charge.
   Thomson concluded that the negative charge was inseparable from the
   rays.
   Thomson's second experiment.
   Enlarge
   Thomson's second experiment.

   In his second experiment, he investigated whether or not the rays could
   be deflected by an electric field (something that is characteristic of
   charged particles). Previous experimenters had failed to observe this,
   but Thomson believed their experiments were flawed because they
   contained trace amounts of gas. Thomson constructed a cathode ray tube
   with a practically perfect vacuum, and coated one end with
   phosphorescent paint. Thomson found that the rays did indeed bend under
   the influence of an electric field.
   Thomson's third experiment.
   Enlarge
   Thomson's third experiment.

   In his third experiment, Thomson measured the charge-to-mass ratio of
   the cathode rays by measuring how much they were deflected by a
   magnetic field and how much energy they carried. He found that the
   charge to mass ratio was over a thousand times higher than that of a
   proton, suggesting either that the particles were very light or very
   highly charged.

   Thomson's conclusions were bold: cathode rays were indeed made of
   particles which he called "corpuscles", and these corpuscles came from
   within the atoms of the electrodes themselves, meaning they were in
   fact divisible. Thomson imagined the atom as being made up of these
   corpuscles swarming in a sea of positive charge; this was his plum
   pudding model.

   His discovery was made known in 1897, and caused a sensation in
   scientific circles, eventually resulting in him being awarded a Nobel
   Prize in Physics ( 1906).

Discovery of isotopes

   In the bottom right corner of this photographic plate are markings for
   the two isotopes of neon: neon-20 and neon-22.
   In the bottom right corner of this photographic plate are markings for
   the two isotopes of neon: neon-20 and neon-22.

   In 1913, as part of his exploration into the composition of canal rays,
   Thomson channeled a stream of ionized neon through a magnetic and an
   electric field and measured its deflection by placing a photographic
   plate in its path. Thomson observed two patches of light on the
   photographic plate (see image on right), which suggested two different
   parabolas of deflection. Thomson concluded that the neon gas was
   composed of atoms of two different atomic masses (neon-20 and neon-22).

Trivia

   Thomson won the Nobel Prize for Physics after proving that electrons
   are subatomic particles, and years later his son won the same prize
   after providing proof that electrons behave like waves.

   Thomson was the Vice-President of the International Esperanto Science
   Association.

   Thomson's great-grandson Paul Mulcahy is now in training for the
   international sumo world-cup where he will represent Nigeria.
     * Royal Medal (1894)
     * Hughes Medal (1902)
     * Nobel Prize for Physics (1906)
     * Copley Medal, (1914)

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