Nano-Biotechnology

111 Years Ago, Thomson Discovered the Electron

The first discovered subatomic particle

By Gabriel Gache, Science News Editor

30th of April 2008, 09:56 GMT

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On 30 April 1897, at the Royal Institution Friday Evening Discourse, Joseph John Thomson announced that he had discovered 'corpuscles', bodies smaller than the hydrogen atom and bearing a negative electric charge. These corpuscles were later named 'electrons', and were the first subatomic

particles ever discovered. The word electron actually comes from the Greek word for 'amber', which was used in ancient times to generate electrical charges while rubbing it against fur.

Thomson would write upon his discovery: "Could anything at first sight seem more impractical than a body which is so small that its mass is an insignificant fraction of the mass of an atom of hydrogen?"

While he was the director of the Cavendish Laboratory at the University of Cambridge, Thomson conducted a series of experiments involving cathode ray tubes. The cathode ray tubes built by him were basically vacuumed glass cylinders inside which two electrodes were placed. When applying voltage between the two electrodes, electrons were being emitted causing the tube to glow in visible light - cathode ray tubes are still used for the displays of many television designs.

Thomson would later notice that the electron beam generated between the two electrodes is deviated both inside magnetic and electric fields, thus he concluded that electrons must bear charge - electrons beams inside television cathode ray tubes are deflected with the help of electric fields.

Thomson calculated that the mass-to-charge ration of the electrons was about one thousand times smaller than that of the hydrogen ion, therefore electrons would either have to have a very high electric charge or a very low mass.

At the time of the discovery, many physicists remained skeptical to whether particles smaller than the atom could indeed exist or not. Nonetheless, only nine years after the announcement of his discovery, Joseph John Thomson was awarded the Nobel Prize for Physics. Thomson is also the first to discover isotopes and is credited with the invention of the mass spectrometer.

TAGS:

electron | atom | spectrometer | cathode ray tube | television

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