His nonmathematical atomic theory-unlike early quantum theory-could also be used to account for chemical bonding and molecular structure (see Gilbert Newton Lewis and Irving Langmuir). Of all the physicists associated with determining the structure of the atom, Thomson remained most closely aligned to the chemical community. He was a good lecturer, encouraged his students, and devoted considerable attention to the wider problems of science teaching at university and secondary levels. Even though he was clumsy with his hands, he had a genius for designing apparatus and diagnosing its problems. In 1884 he was named to the prestigious Cavendish Professorship of Experimental Physics at Cambridge, although he had personally done very little experimental work. He was then recommended to Trinity College, Cambridge, where he became a mathematical physicist. Instead young Thomson attended Owens College, Manchester, which had an excellent science faculty. His father intended him to be an engineer, which in those days required an apprenticeship, but his family could not raise the necessary fee. Ironically, Thomson-great scientist and physics mentor-became a physicist by default. These results were the first to show that atoms are indeed divisible and were the basis for the first atomic model.From "The Growth of Physical Science," by Sir James Hopwood Jeans (Cambridge: Cambridge University Press, 1948) Early Life and Education Further, because the mass of an electron is so much smaller than that of an entire atom, there must be other particles present in the atom to account for the majority of its mass. Since electrons have a negative charge, and all atoms are electrically neutral, there must also be a positive charge present in the atom. He reasoned that since cathode rays show the same deflection for any gas used, electrons must be present in the atoms of all elements. Using this number, and Thompson's charge-to-mass ratio, he was able to calculate the mass of one electron. Using these data, he calculated that the charge of every oil droplet was a multiple of the same number each time, and concluded that this must be the charge of a single electron. He varied the charge on the two plates and measured how this change affected the droplets' rate of fall. He then sprayed these droplets through an apparatus, allowing them to fall between two electrically charged plates. He used x rays to give oil droplets a negative charge. In 1909, he discovered that the mass of one electron is approximately one two-thousandth that of a hydrogen atom through his "oil droplet" experiments. Millikan (1868–1953) of the University of Chicago performed experiments that further confirmed Thomson's results. He then concluded that all cathode rays are made up of the same particles, which were later named electrons by another English physicist, G. Thomson found that the charge-to-mass ratio was always the same, regardless of the materials used. His experiments demonstrated that the amount of deflection could be predicted mathematically. Thompson performed the same experiments using different metals for the cathode and anode as well as different gases inside the tube.
#RESULTS OF CATHODE RAY EXPERIMENT SERIES#
Thomson performed a series of experiments in which he was able to determine the ratio of the charge of the particles that make up the cathode ray to their mass by measuring the deflection of the rays with varying magnetic and electric fields. Therefore, it was concluded that the particles that compose a cathode ray not only had mass but also a negative charge.Įnglish physicist Joseph John Thomson (1856–1940) confirmed these findings in 1897. When exposed to a magnetic field, the cathode ray was deflected in the same manner as an electric current, which has a negative charge. When a paddle wheel was placed in the tube, it rolled from cathode to anode, which showed that the particles making up the cathode ray had mass. This stream of particles was called a cathode ray. It was hypothesized that a stream of particles originating at the cathode and moving toward the anode caused the glow. Early experiments showed that the current caused the surface of the tube directly opposite the cathode to glow. The voltage source creates a current that can be passed through the gas trapped inside. The cathode and anode are attached to a voltage source. At one end of the tube is a cathode, at the other end, an anode. A cathode ray tube is a partially evacuated glass tube containing a gas at low pressure. In the late 1800s, the cathode ray tube was developed and used in several investigations. The discovery of the first subatomic particle, the electron, resulted from experiments involving the effects of electricity on matter.
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