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I am reading about A cathode ray discharge tube and I still do not fully understand why that as you keep on lowering the pressure in the chamber it creates striations, Faraday's dark space and Crooke's dark space and why it does not just stay as a constant stream of light? Also why does the gas have to be at a low pressure in the first place for the constant column of light to appear?

To verify my questions are:

  1. Why when you lower the pressure to a certain extent you can see striations, Faraday's dark space and Crooke's dark space and why doesn't it just stay as a constant column of light?
  2. Why does the pressure in the chamber have to be very low for you to be able to see a constant column of light?
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The most important question is why do we need low pressures? If you recall kinetic theory of gases, there is a concept of mean free path. This quantity roughly tells us the distance a particle would travel before colliding with another particle. If you want the electrons to travel from one end to the other, you need to provide a large mean free path to them. How can one obtain that? Simply by removing "matter" from the cathode ray tube. Practically this is achieved by vacuum pumps. Although nobody gives importance to vacuum pumps, it was this technology which allowed great progress in the field of cathode ray experiments and hence understanding matter.

Now, the "glow" phenomenon is rather a spectroscopic problem. Electron don't glow green/pink etc, it is the matter which starts to glow when it interacts with electron. The glow can originate from several sources such as recombination phenomenon, fluorescence of the glass, a fluorescent zinc sulfide screen placed inside, or even Xrays. When the pressures are moderate, other phenomena like which you quote as striations, appear. This arises from accelerated electrons exciting the gas particles and then losing energy (dark space). This video explains some of it. Cathode ray striations. However it is not a trivial phenomena. It took ages to understand it. The observation of striations indicate that there is enough gas (low vacuum) in the discharge tube.

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