![]() ![]() From the perception of solid matter, it was presumed that this positive residual matter filled the entire space of the atom, giving rise to what has been called the " Thomson model" of the atom. It was known that electrons could be removed from atoms, and that they became positive ions as a result. With the combined results of Thomson and Millikan, a value for the electron mass was obtained - a value far below that of atoms. The determination of the charge of the electron awaited the work of Millikan who measured the electron charge in 1909 with his oil drop experiment. ![]() Using this apparatus, Thomson determined the charge-to-mass ratio of the electron, e/m. Thomson’s First Cathode Ray Experiment Thomson had an inkling that the ‘rays’ emitted from the electron gun were inseparable from the latent charge, and decided to try and prove this by using a magnetic field. This same principle is presently used in velocity selectors for mass spectrometers. Thomson constructed some elegant experiments to find a definitive and comprehensive answer about the nature of cathode rays. Thomson showed that with the application of both electric and magnetic fields, he could balance the deflections and obtain a straight beam. A narrow luminous beam could be produced by using an aperture near the cathode, and this beam could be deflected by either an electric field or a magnetic field. ![]() In the 1890's, cathode ray tubes had been developed in which a luminous beam could be produced in a partially evacuated glass tube, directed from the negative electrode (cathode) to the positive (anode). Sir Joseph John Thomson (1856-1940) played a pivotal role in developing our understanding of the electron. ![]()
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