Thomson boiled down the findings of his 1897 experiments into three primary hypotheses: (1) Cathode rays are charged particles, which he called "corpuscles. Subsequent experiments by Philipp Lenard and others over the next two years confirmed the conclusion that the cathode rays were particles with a mass far smaller than that of any atom. Just as Emil Wiechert had reported earlier in the year, the mass-to-charge ratio for cathode rays turned out to be over one thousand times smaller than that of a charged hydrogen atom.
He collected data using a variety of tubes filled with different gases. Although he couldn't measure directly the mass or electric charge of such a particle, he could measure how much the rays were bent by a magnetic field, and how much energy they carried, which would enable him to calculate the ratio of the mass of a particle to its electrical charge (m/e). However, he still lacked experimental data on what these particles actually were, and hence undertook a third experiment to determine their basic properties. From these two experiments, Thomson concluded, "I can see no escape from the conclusion that (cathode rays) are charges of negative electricity carried by particles of matter." Under these circumstances, the cathode rays did bend with the application of an electric field. Thomson theorized that the traces of gas remaining in the tube were being turned into an electrical conductor by the cathode rays themselves, and managed to extract nearly all of the gas from the tube to test his hypothesis. A charged particle will curve as it moves through an electric field, but not if it is surrounded by a conducting material. Failing this, he concluded that the negative charge and the cathode rays were somehow stuck together.Īll previous attempts to bend cathode rays with an electric field had failed, so Thomson devised a new approach in a second pivotal experiment. The purpose was to determine if, by bending the rays with a magnet, Thomson could separate the charge from the rays. First, in a variation of a pivotal 1895 experiment by Jean Perrin, he built a pair of cathode ray tubes ending in a pair of metal cylinders with a slit in them, which were in turn connected to an electrometer. Three of his experiments proved especially conclusive. Thomson refined previous experiments and designed new ones in his quest to uncover the true nature of these mysterious cathode rays. Scientists theorized that the glow was produced by some kind of ray emitted by the cathode, but it took the seminal research of a British professor in Cambridge University's Cavendish Laboratory to finally provide a solution to the puzzle. The result: the interior of the tube would glow in lovely fluorescent patterns. They took a glass tube with wires embedded in opposite ends, administered a high voltage and pumped out most of the air. Science lecturers traveling from town to town in the mid-19th century delighted audiences with a device that could be considered the ancestor of the neon sign. THE SMALLEST AND LIGHTEST POSITIVE ION WAS OBTAINED FROM HYDROGEN AND WAS CALLED PROTON.October 1897: The Discovery of the Electron The behavior of these particles in a magnetic or electric field is opposite to that of electrons or cathode rays. Some positively charged particles carry a multiple of a fundamental unit of electric charge.Ĥ. The charge to mass ratio of particles depends on the gas from which it originates.ģ. Those are simply the positively charged gaseous ions.Ģ. The positively charged particles depend upon the nature of gas present in the cathode ray tube. The experiment for canal rays was carried out in modified cathode ray tube, by E.
the cathode rays consist of electrons, while the anode/canal rays are the positively charged gaseous ions. You are right, both kinds of rays are emitted simultaneously. The gold foil was surrounded by a detector screen that would flash when hit with an α \alpha α alpha particle. Most of the radiation was absorbed by the lead, but a thin beam of α \alpha α alpha particles escaped out of the pinhole in the direction of the gold foil. In this case, Rutherford placed a sample of radium (a radioactive metal) inside a lead box with a small pinhole in it. Alpha particles are helium nuclei ( 2 4 He 2 + ) (_2^4\text) ( 2 4 He 2 + ) left parenthesis, start subscript, 2, end subscript, start superscript, 4, end superscript, start text, H, e, end text, start superscript, 2, plus, end superscript, right parenthesis, and they are given off in various radioactive decay processes. In his famous gold foil experiment, Rutherford fired a thin beam of α \alpha α alpha particles (pronounced alpha particles) at a very thin sheet of pure gold. The next groundbreaking experiment in the history of the atom was performed by Ernest Rutherford, a physicist from New Zealand who spent most of his career in England and Canada.
0 kommentar(er)
