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The Discovery of Electron
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2007-9-13
Electron is a kind of elementary particle with unit negative electric charge that people discovered the earliest time. The British physicist Joseph John Thomson was the first man proving the existence of electron with experiment as earlier as in 1897.
Thomson was a remarkable and fruitful physicist. When he was 28, he became a member of British Royal Academy of Sciences and was appointed as the director of world famous Cavendish Laboratory. The discovery of X-rays especially it capability to image display life-form's skeleton penetrating through life organism greatly encouraged the researchers working with Cavendish Laboratory. Thomson agreed with Crookes point of view who believed it was a kind of electrified atom.
What kind of thing that causes X-ray to produce cathode rays? There was a big argument between Germany and British scientists on this issue. Germany physicist Hertz made his declaration in 1892 that cathode ray was a kind of ether wave rather than a particle. All other Germany physicists went along with this point of view; however British physicists represented by Crookes insisted that cathode ray was a kind of electrified particle stream; in such circumstance, the sensitive Thomson concentrated himself in this argument on the nature of cathode ray.
In 1895, the young French physicist Perrin talked about the experiment on determining the electric quantity of cathode ray in his doctoral thesis. He made cathode ray entering into a cathode space through a small hole to Faraday cup for collecting electric charge, so the electrometer displayed it carried negative electricity; when placing cathode ray tube between the magnetic poles, cathode ray could not be entered into the small hole due to its deflexion, at this time the electricity on the electricity collector disappeared proving that the electric charge was carried by cathode ray. Perrin revealed his point of view through this experiment that cathode ray was negative charged particle stream, however he believed that this particle was gaseous ion. Germany physicists who insisted that cathode ray was ether wave immediately argued back to this experiment for the reason that, enough cathode ray generated negative charged particle, it was still lack of evidence to prove its consistency with cathode ray path, therefore the electric charge displayed on the electrometer might not come from cathode ray.
Thomson believed that Perrin experiment design left some space for the scientists with ether wave point of view; for removing this space, Thomson especially designed a smart experiment device for reworking Perrin¡¯s experiment. He placed two gaped coaxial cylinders in a glass bulb connecting to discharge tube; the cathode ray coming from Cathode A was led into this bulb through the metal plug at the bottle neck; the metal plug was connected to Cathode B. In this way, the cathode ray would not drop down to the cylinder unless the cathode ray was deflected by the magnet. The external cylinder was grounded and the internal cylinder was connected to the electroscope. When the cathode ray did not drop down to the gap, the electric charge delivered to the electroscope was very few; when the cathode ray was deflected by the magnet and led down to the gap, a large quantity of electric charge was transported to the electroscope. The quantity of electric charge was so amazing: sometimes the negative electric charge going through the gap within one second was quite enough to change 1.5 microfarad capacitance to 20 volts. If the cathode ray was deflected by big range by the magnetic field even out of the cylinder gap, the electric charge entering into the cylinder would be dropped down to a little of that when it shot the target. In conclusion, the experiment revealed that no matter how the magnetic field twisted or deflected the cathode ray, the negative charged particle had a close relationship with the cathode ray. This experiment proves that cathode ray and negative charged particle follow the same path under the function imposed by magnetic field so that it proves cathode ray consists of negative charged particles. The argument no longer was argued. This discovery had a great significance for the future development of human understanding on electron.
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Organizer:
Beijing Municipal Association for Science & Technology
Undertaker: Beijing Science & Technology
Consulting Center,
Information Center of Beijing Municipal Association for
Science & Technology |
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