![]() ![]() The particles, first named corpuscles, were later called electrons. By examining both the energy of the rays and the amount by which an electric charge deflected them, Thomson was able to calculate that these particles had one two-thousandth the mass of a hydrogen atom. Other experimental results, some by other scientists, suggested that the ratio of the charge to the mass of these particles had to be less than one-thousandth the ratio for charged hydrogen atoms. If they had momentum, that meant (in the physics of the time) that they had mass, suggesting that the rays were composed of tiny particles. A series of experiments in which various objects were placed in the path of the rays showed that they also had momentum (they would cause a small paddle wheel to turn, for example). Thomson examined the nature of the rays' charge by bringing a positively charged and a negatively charged plate near the path of the rays, and observed that the rays were deflected toward the positive plate, suggesting they had negative charge. As an electric current passed from the cathode at one end of the tube to the anode at the other, raylike emanations were seen to proceed from the cathode to the anode. Thomson was studying what we now call cathode-ray tubes. The breakthroughs came in the late 1890s, when the British physicist J. Biography Nowadays we take for granted the existence of electrons, but this was not true just over 100 years ago, when the atom was thought to be a single unit that had no parts.
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