SIR JOSEPH JOHN THOMSON OM PRS (/ˈtɒmsən/ ; 18 December 1856 – 30 August 1940) was an English physicist and Nobel laureate in physics , credited with the discovery and identification of the electron ; and with the discovery of the first subatomic particle .
In 1897, Thomson showed that cathode rays were composed of previously unknown negatively charged particles, which he calculated must have bodies much smaller than atoms and a very large value for their charge-to-mass ratio . Thomson is also credited with finding the first evidence for isotopes of a stable (non-radioactive) element in 1913, as part of his exploration into the composition of canal rays (positive ions). His experiments to determine the nature of positively charged particles, with Francis William Aston , were the first use of mass spectrometry and led to the development of the mass spectrograph.
Thomson was awarded the 1906 Nobel Prize in
* 1 Education and personal life
* 2 Career and research
* 2.1 Overview * 2.2 Early work * 2.3 Discovery of the electron * 2.4 Isotopes and mass spectrometry
* 2.5 Experiments with cathode rays
* 2.5.1 Magnetic deflection * 2.5.2 Electrical charge * 2.5.3 Electrical deflection * 2.5.4 Measurement of mass to charge ratio * 2.5.5 Conclusions
* 2.6 Other work
* 2.7 Awards and honours
* 2.7.1 Posthumous honours
* 3 References * 4 Bibliography * 5 External links
EDUCATION AND PERSONAL LIFE
Joseph John Thomson was born 18 December 1856 in
Cheetham Hill ,
His early education was in small private schools where he
demonstrated outstanding talent and interest in science. In 1870 he
was admitted to
Owens College in
One of Thomson's greatest contributions to modern science was in his
role as a highly gifted teacher. One of his students was Ernest
Rutherford , who later succeeded him as Cavendish Professor of Physics
. In addition to Thomson himself, eight of his research assistants
Francis William Aston ,
Charles Glover Barkla ,
Thomson's prize-winning master's work, Treatise on the motion of vortex rings, shows his early interest in atomic structure. In it, Thomson mathematically described the motions of William Thomson 's vortex theory of atoms.
Thomson published a number of papers addressing both mathematical and
experimental issues of electromagnetism. He examined the
electromagnetic theory of light of
James Clerk Maxwell
Much of his work in mathematical modelling of chemical processes can be thought of as early computational chemistry . In further work, published in book form as Applications of dynamics to physics and chemistry (1888), Thomson addressed the transformation of energy in mathematical and theoretical terms, suggesting that all energy might be kinetic. His next book, Notes on recent researches in electricity and magnetism (1893), built upon Maxwell's Treatise upon electricity and magnetism, and was sometimes referred to as "the third volume of Maxwell". In it, Thomson emphasized physical methods and experimentation and included extensive figures and diagrams of apparatus, including a number for the passage of electricity through gases. His third book, Elements of the mathematical theory of electricity and magnetism (1895) was a readable introduction to a wide variety of subjects, and achieved considerable popularity as a textbook.
A series of four lectures, given by Thomson on a visit to Princeton University in 1896, were subsequently published as Discharge of electricity through gases (1897). Thomson also presented a series of six lectures at Yale University in 1904.
DISCOVERY OF THE ELECTRON
Several scientists, such as
In April 1897, Thomson had only early indications that the cathode rays could be deflected electrically (previous investigators such as Heinrich Hertz had thought they could not be). A month after Thomson's announcement of the corpuscle, he found that he could reliably deflect the rays by an electric field if he evacuated the discharge tube to a very low pressure. By comparing the deflection of a beam of cathode rays by electric and magnetic fields he obtained more robust measurements of the mass to charge ratio that confirmed his previous estimates. This became the classic means of measuring the charge and mass of the electron.
Thomson believed that the corpuscles emerged from the atoms of the trace gas inside his cathode ray tubes . He thus concluded that atoms were divisible, and that the corpuscles were their building blocks. In 1904 Thomson suggested a model of the atom, hypothesizing that it was a sphere of positive matter within which electrostatic forces determined the positioning of the corpuscles. To explain the overall neutral charge of the atom, he proposed that the corpuscles were distributed in a uniform sea of positive charge. In this "plum pudding" model the electrons were seen as embedded in the positive charge like plums in a plum pudding (although in Thomson's model they were not stationary, but orbiting rapidly).
ISOTOPES AND MASS SPECTROMETRY
In the bottom right corner of this photographic plate are markings for the two isotopes of neon: neon-20 and neon-22.
In 1912, as part of his exploration into the composition of the streams of positively charged particles then known as canal rays , Thomson and his research assistant F. W. Aston channelled a stream of neon ions through a magnetic and an electric field and measured its deflection by placing a photographic plate in its path. They observed two patches of light on the photographic plate (see image on right), which suggested two different parabolas of deflection, and concluded that neon is composed of atoms of two different atomic masses (neon-20 and neon-22), that is to say of two isotopes . This was the first evidence for isotopes of a stable element; Frederick Soddy had previously proposed the existence of isotopes to explain the decay of certain radioactive elements.
J.J. Thomson's separation of neon isotopes by their mass was the first example of mass spectrometry , which was subsequently improved and developed into a general method by F. W. Aston and by A. J. Dempster .
EXPERIMENTS WITH CATHODE RAYS
Earlier, physicists debated whether cathode rays were immaterial like light ("some process in the aether ") or were "in fact wholly material, and ... mark the paths of particles of matter charged with negative electricity", quoting Thomson. The aetherial hypothesis was vague, but the particle hypothesis was definite enough for Thomson to test.
Thomson first investigated the magnetic deflection of cathode rays. Cathode rays were produced in the side tube on the left of the apparatus and passed through the anode into the main bell jar , where they were deflected by a magnet. Thomson detected their path by the fluorescence on a squared screen in the jar. He found that whatever the material of the anode and the gas in the jar, the deflection of the rays was the same, suggesting that the rays were of the same form whatever their origin.
The cathode ray tube by which J.J. Thomson demonstrated that cathode rays could be deflected by a magnetic field, and that their negative charge was not a separate phenomenon.
While supporters of the aetherial theory accepted the possibility that negatively charged particles are produced in Crookes tubes , they believed that they are a mere by-product and that the cathode rays themselves are immaterial. Thomson set out to investigate whether or not he could actually separate the charge from the rays.
Thomson constructed a
Thomson's illustration of the
In May–June 1897, Thomson investigated whether or not the rays could be deflected by an electric field. Previous experimenters had failed to observe this, but Thomson believed their experiments were flawed because their tubes contained too much gas.
Thomson constructed a
When the upper plate was connected to the negative pole of the battery and the lower plate to the positive pole, the glowing patch moved downwards, and when the polarity was reversed, the patch moved upwards.
Measurement Of Mass To Charge Ratio
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. He used the same apparatus as in his previous experiment, but placed the discharge tube between the poles of a large electromagnet. He found that the mass to charge ratio was over a thousand times lower than that of a hydrogen ion (H+), suggesting either that the particles were very light and/or very highly charged. Significantly, the rays from every cathode yielded the same mass-to-charge ratio. This is in contrast to anode rays (now known to arise from positive ions emitted by the anode), where the mass-to-charge ratio varies from anode-to-anode. Thomson himself remained critical of what his work established, in his Nobel Prize acceptance speech referring to "corpuscles" rather than "electrons".
Thomson's calculations can be summarised as follows (notice that we reproduce here Thomson's original notations, using F instead of E for the electric field and H instead of B for the magnetic field):
The electric deflection is given by Θ = Fel/mv2 where Θ is the angular electric deflection, F is applied electric intensity, e is the charge of the cathode ray particles, l is the length of the electric plates, m is the mass of the cathode ray particles and v is the velocity of the cathode ray particles.
The magnetic deflection is given by φ = Hel/mv where φ is the angular magnetic deflection and H is the applied magnetic field intensity.
The magnetic field was varied until the magnetic and electric deflections were the same, when Θ = φ and Fel/mv2= Hel/mv. This can be simplified to give m/e = H2l/FΘ. The electric deflection was measured separately to give Θ and H, F and l were known, so m/e could be calculated.
As the cathode rays carry a charge of negative electricity, are
deflected by an electrostatic force as if they were negatively
electrified, and are acted on by a magnetic force in just the way in
which this force would act on a negatively electrified body moving
along the path of these rays, I can see no escape from the conclusion
that they are charges of negative electricity carried by particles of
J. J. Thomson
As to the source of these particles, Thomson believed they emerged from the molecules of gas in the vicinity of the cathode.
If, in the very intense electric field in the neighbourhood of the
cathode, the molecules of the gas are dissociated and are split up,
not into the ordinary chemical atoms, but into these primordial atoms,
which we shall for brevity call corpuscles; and if these corpuscles
are charged with electricity and projected from the cathode by the
electric field, they would behave exactly like the cathode rays.
J. J. Thomson
Thomson imagined the atom as being made up of these corpuscles orbiting in a sea of positive charge; this was his plum pudding model . This model was later proved incorrect when his student Ernest Rutherford showed that the positive charge is concentrated in the nucleus of the atom.
In 1905, Thomson discovered the natural radioactivity of potassium .
In 1906, Thomson demonstrated that hydrogen had only a single electron per atom. Previous theories allowed various numbers of electrons.
AWARDS AND HONOURS
Thomson was elected a
Fellow of the Royal Society
Adams Prize (1882)
Royal Medal (1894)
Thomson was elected a
Fellow of the Royal Society
In 1991, the thomson (symbol: Th) was proposed as a unit to measure mass-to-charge ratio in mass spectrometry in his honour.
J J Thomson Avenue, on the University of
In November 1927, J.J. Thomson opened the Thomson building, named in his honour, in the Leys School , Cambridge.
* ^ A B C Rayleigh (1941). "Joseph John Thomson. 1856-1940".
Obituary Notices of Fellows of the
* ^ Dahl (1997) , p. 324: "Thomson\'s model, then, consisted of a
uniformly charged sphere of positive electricity (the pudding), with
discrete corpuscles (the plums) rotating about the center in circular
orbits, whose total charge was equal and opposite to the positive
* ^ J.J. Thomson (1912) "Further experiments on positive rays,"
Philosophical Magazine, series 6, 24 (140): 209–253.
* ^ J.J. Thomson (1913) "Rays of positive electricity," Proceedings
* Thomson, George Paget. (1964) J.J. Thomson: Discoverer of the
Electron. Great Britain: Thomas Nelson with Application of the Results
to the Theory of Atomic Structure," Philosophical Magazine Series 6,
Volume 7, Number 39, pp. 237–265. This paper presents the classical
"plum pudding model " from which the
Thomson Problem is posed.
* The Master of Trinity at Trinity College,
* Resources in your library * Resources in other libraries
BY J. J. THOMSON
* Online books * Resources in your library * Resources in other libraries
* Media related to Joseph John Thomson at Wikimedia Commons
* Works written by or about
J. J. Thomson
* v * t * e
Copley Medallists of 1901–50
Josiah Willard Gibbs
* v * t * e
Laureates of the Nobel Prize in
* 1901 Röntgen * 1902 Lorentz / Zeeman * 1903 Becquerel / P. Curie / M. Curie * 1904 Rayleigh * 1905 Lenard * 1906 J. J. Thomson * 1907 Michelson * 1908 Lippmann * 1909 Marconi / Braun * 1910 Van der Waals * 1911 Wien * 1912 Dalén * 1913 Kamerlingh Onnes * 1914 Laue * 1915 W. L. Bragg / W. H. Bragg * 1916 * 1917 Barkla * 1918 Planck * 1919 Stark * 1920 Guillaume * 1921 Einstein * 1922 N. Bohr * 1923 Millikan * 1924 M. Siegbahn * 1925 Franck / Hertz
* 1926 Perrin * 1927 Compton / C. Wilson * 1928 O. Richardson * 1929 De Broglie * 1930 Raman * 1931 * 1932 Heisenberg * 1933 Schrödinger / Dirac * 1934 * 1935 Chadwick * 1936 Hess / C. D. Anderson * 1937 Davisson / G. P. Thomson * 1938 Fermi * 1939 Lawrence * 1940 * 1941 * 1942 * 1943 Stern * 1944 Rabi * 1945 Pauli * 1946 Bridgman * 1947 Appleton * 1948 Blackett * 1949 Yukawa * 1950 Powell
* 1951 Cockcroft / Walton * 1952 Bloch / Purcell * 1953 Zernike * 1954 Born / Bothe * 1955 Lamb / Kusch * 1956 Shockley / Bardeen / Brattain * 1957 C. N. Yang / T. D. Lee * 1958 Cherenkov / Frank / Tamm * 1959 Segrè / Chamberlain * 1960 Glaser * 1961 Hofstadter / Mössbauer * 1962 Landau * 1963 Wigner / Goeppert-Mayer / Jensen * 1964 Townes / Basov / Prokhorov * 1965 Tomonaga / Schwinger / Feynman * 1966 Kastler * 1967 Bethe * 1968 Alvarez * 1969 Gell-Mann * 1970 Alfvén / Néel * 1971 Gabor * 1972 Bardeen / Cooper / Schrieffer * 1973 Esaki / Giaever / Josephson * 1974 Ryle / Hewish * 1975 A. Bohr / Mottelson / Rainwater
* 1976 Richter / Ting * 1977 P. W. Anderson / Mott / Van Vleck * 1978 Kapitsa / Penzias / R. Wilson * 1979 Glashow / Salam / Weinberg * 1980 Cronin / Fitch * 1981 Bloembergen / Schawlow / K. Siegbahn * 1982 K. Wilson * 1983 Chandrasekhar / Fowler * 1984 Rubbia / Van der Meer * 1985 von Klitzing * 1986 Ruska / Binnig / Rohrer * 1987 Bednorz / Müller * 1988 Lederman / Schwartz / Steinberger * 1989 Ramsey / Dehmelt / Paul * 1990 Friedman / Kendall / R. Taylor * 1991 de Gennes * 1992 Charpak * 1993 Hulse / J. Taylor * 1994 Brockhouse / Shull * 1995 Perl / Reines * 1996 D. Lee / Osheroff / R. Richardson * 1997 Chu / Cohen-Tannoudji / Phillips * 1998 Laughlin / Störmer / Tsui * 1999 \'t Hooft / Veltman * 2000 Alferov / Kroemer / Kilby
* 2001 Cornell / Ketterle / Wieman * 2002 Davis / Koshiba / Giacconi * 2003 Abrikosov / Ginzburg / Leggett * 2004 Gross / Politzer / Wilczek * 2005 Glauber / Hall / Hänsch * 2006 Mather / Smoot * 2007 Fert / Grünberg * 2008 Nambu / Kobayashi / Maskawa * 2009 Kao / Boyle / Smith * 2010 Geim / Novoselov * 2011 Perlmutter / Riess / Schmidt * 2012 Wineland / Haroche * 2013 Englert / Higgs * 2014 Akasaki / Amano / Nakamura * 2015 Kajita / McDonald * 2016 Thouless / Haldane / Kosterlitz
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Presidents of the
* Viscount Brouncker (1662)
* Joseph Williamson (1677)
Christopher Wren (1680)
* John Hoskyns (1682)
Cyril Wyche (1683)
William Hyde Wollaston (1820)
William Huggins (1900)
* Lord Rayleigh (1905)
Archibald Geikie (1908)
William Crookes (1913)
J. J. Thomson
* v * t * e
Scientists whose names are used as non SI units
Anders Jonas Ångström
Alexander Graham Bell
* Scientists whose names are used as SI units * Scientists whose names are used in chemical element names * Scientists whose names are used in physical constants
* v * t * e
Scientists whose names are used in physical constants
LIST OF SCIENTISTS WHOSE NAMES ARE USED AS SI UNITS AND NON SI UNITS
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