He concluded that they were small particles with a negative electric charge and not much mass. He used his famous three experiments to make an argument about what the "rays" were. What Thomson did is set up an experiment where, among other things, he got a much better vacuum than previous experimenters, which allowed him to measure the "rays" much more delicately. The question was, what are these things? There had been lots of contradictory reports about their mass, whether they had a charge or not, and so on. They were known to exist since the 1860s. "Cathode rays" were particles produced when electricity is run through a vacuum in a specific type of tube. Geissler tubes, Crookes tubes, and, cathode ray tubes just describe different types of "discharge tubes" that electricity is being run through in one configuration or another. So tubes of this nature were quite common. These tubes were available for order by catalogue and were used both for physics experiments as well as for entertaining the public (which could fund more physics experiments). These ranged from strange colors to strange patterns, and (sometime later) even invisible, penetrating rays (X-rays). Drawing the required vacuum would have been within the technology of the day.Īs for historical context, people realized around 1855 or so that if you filled tubes with air (or a lack of air) and shot electricity through them, you got "weird" results. The outer housing would be pretty easy for a skilled glassblower to make. As for how they were made, most of the internal components are pretty straightforward. He probably didn't see the future that they had in consumer electronics, but those devices are far more complicated anyway. To directly answer your question: JJ Thompson knew exactly what his CRT was for-measuring the properties of an electron. It should be clear that this is a much more advanced technology. By oscillating the power on those sets of plates and then varying the strength of the electron beam it is possible to generate an image. That changed when someone realized that you could take one pair of parallel plates and use them to deflect the electron stream in the up/down axis, then another set of parallel plates and use that to deflect the electrons in the left/right axis. By that time the idea of a CRT was old news but it wasn't anything more than a highly specialized piece of lab equipment. The CRT used in a TV is much more advanced, which stands to reason since it was developed so much later. By measuring the shape of that arc JJ Thompson was able to figure out the ratio of charge to mass (he couldn't nail down either number individually since a high charge and high mass would manifest the same as a low charge and low mass, but he could at least find the ratio). Further down in the apparatus they are deflected in an arc. These electrons then get accelerated by a couple of parallel plates. When electricity is passed through that filament it starts shedding electrons (or at least that was how that aspect was explained to me). Thus, the CRT he built (or at least the one I used when I repeated his experiment) uses a small filament similar to what is inside of an incandescent light bulb. Namely, he wanted to shoot electrons at some speed then cause them to change direction. The one that JJ Thompson made was purpose built with a specific experiment in mind. The CRT that JJ Thompson used is much, much simpler than the one in old TVs and monitors.
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