4 ms·

> Electrons move more slowly in a solid than in a vacuum My understanding is that electrons wouldn't move at all in a vacuum because they require a conductor.

• privong 12y ago
  > My understanding is that electrons wouldn't move at all in a vacuum because they require a conductor. Electrons can propagae in the absense of a medium, in addition to within a conductor. You might thinking of their motion through conductors relative to insulators; but in that comparison, electrons don't (readily) move through insulators because they are impeded. In the particular case of a vacuum tube, the electrons are freed from the surface of the filament, where they travel through the vacuum in a tube and are attracted via electrostatic forces, to the positively charged plate at the top of the tube.
  • sjtrny 12y ago
    Could the absence of a medium also be considered an insulator? The description of Thermionic emission on Wikipedia (http://en.m.wikipedia.org/wiki/Thermionic_emission http://en.m.wikipedia.org/wiki/Thermionic_emission) seems general enough that things like rubber and vacuums are both insulators in some sense.
    • privong 12y ago
      Thermionic emission just refers to releasing electrons from the surface of a material by heating up that material (which is what happens in a vacuum tube). But it doesn't specifically deal with what happens to the electrons after they leave the surface of the material. I am not sure what part of the wikipedia article you are referring to – the word "insulator" isn't used anywhere in the article.
    • tjradcliffe 12y ago
      "Insulator" usually means "made of insulating material", and a vacuum is not made of material. :-) Language is ambiguous, so it's important when asking questions like this to be really clear about what you mean by terms. In particular: "insulator" is a term of convenience that groups together materials of sufficiently low conductivity under fairly normal conditions. What constitutes "sufficiently low" and "fairly normal" are both highly context dependent. Heat anything up enough and it'll become a conductor (it'll also become a plasma). If you use a term like "insulator" without keeping all this in mind it'll produce some pretty weird results. So you can answer this question all kinds of ways. In normal high-voltage parlance, vacuums are considered insulators. But unlike insulating materials, which are full of electrons that can't move, vacuums are insulators purely because they don't contain any electrons. If you inject electrons, the vacuum becomes a conductor... or at least the electrons do. After all, a vacuum is an absence of matter, and where there is an electron there is matter, so where there is an electron there is not a vacuum...
    • kazinator 12y ago
      Sure. Vacuum is an insulator until you exceed its breakdown voltage, just like other insulators. Electricity will go through a vacuum just like it will go through a polyester film or whatever.
• Johnythree 12y ago
  Then how to Vacuum tubes work?
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