Thomson’s first cathode ray experiment
In 1895, Jean Perrin found that cathode rays deposited and electric charge. Thomson wanted to investigate whether the electric charge can be separated from the cathode ray. He built a cathode ray tube for this experiment (figure 6.9).
At the end of the cathode ray tube, there was a metal cylinder with two slits. The cylinder was connected to an electrometer, a device for catching and measuring small electric charges. Thomson found that the electrometer measured a large amount of negative charge when the cathode rays entered the slits.
When he used a magnet to deflect the cathode rays so that they could not enter the electrometer, the electrometer did not detect any electric charge. The showed that the charge had been bent away from the electrometer, together with the cathode rays. Hence, he concluded that the electric charge cannot be separated from the cathode ray.
Thomson’s second cathode ray experiment
Thomson next tried to prove the hypothesis that the cathode a negative charge. In May-June 1897, he tried to deflect the rays with an electric field. Other physicist before Thomson had attempted to use the same method to bend cathode rays, but all of them failed. Thomson believed this was because the tube contained traces of gas. He constructed a slightly modified cathode ray tube with nearly all of the gas extracted from the tube, creating an almost perfect vacuum
On one end of the tube was the cathode, which emitted cathode rays. The rays could pass through two metal slits – the first slits act as the anode while the second slit was connected to the earth. The two parallel aluminium plates were connected in an electrical circuit. Closing the circuit would create an electric field between the plates, used to be bend the cathode rays. On the other end of the tube was a large glass sphere. Cathode rays that hit the sphere would create a fluorescent patch. Thomson pasted a scale on the surface of the sphere to measure the deflection of the cathode rays.
When Thomson closed the electrical circuit connecting the aluminium plates, he observed the deflection of the cathode rays by the electric field as expected. The dotted blue line shows the path of the cathode ray when the electric field was absent; the solid blue shows the path of the cathode ray when the electric field was present.
When Thomson connected the upper aluminium plate to the negative terminal of the battery and the lower plate to the positive terminal of the battery
Thomson’s first cathode ray experimentIn 1895, Jean Perrin found that cathode rays deposited and electric charge. Thomson wanted to investigate whether the electric charge can be separated from the cathode ray. He built a cathode ray tube for this experiment (figure 6.9).At the end of the cathode ray tube, there was a metal cylinder with two slits. The cylinder was connected to an electrometer, a device for catching and measuring small electric charges. Thomson found that the electrometer measured a large amount of negative charge when the cathode rays entered the slits.When he used a magnet to deflect the cathode rays so that they could not enter the electrometer, the electrometer did not detect any electric charge. The showed that the charge had been bent away from the electrometer, together with the cathode rays. Hence, he concluded that the electric charge cannot be separated from the cathode ray.Thomson’s second cathode ray experimentThomson next tried to prove the hypothesis that the cathode a negative charge. In May-June 1897, he tried to deflect the rays with an electric field. Other physicist before Thomson had attempted to use the same method to bend cathode rays, but all of them failed. Thomson believed this was because the tube contained traces of gas. He constructed a slightly modified cathode ray tube with nearly all of the gas extracted from the tube, creating an almost perfect vacuumOn one end of the tube was the cathode, which emitted cathode rays. The rays could pass through two metal slits – the first slits act as the anode while the second slit was connected to the earth. The two parallel aluminium plates were connected in an electrical circuit. Closing the circuit would create an electric field between the plates, used to be bend the cathode rays. On the other end of the tube was a large glass sphere. Cathode rays that hit the sphere would create a fluorescent patch. Thomson pasted a scale on the surface of the sphere to measure the deflection of the cathode rays.When Thomson closed the electrical circuit connecting the aluminium plates, he observed the deflection of the cathode rays by the electric field as expected. The dotted blue line shows the path of the cathode ray when the electric field was absent; the solid blue shows the path of the cathode ray when the electric field was present.When Thomson connected the upper aluminium plate to the negative terminal of the battery and the lower plate to the positive terminal of the battery
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