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How exactly do cathode ray tubes work?

  1. Aug 16, 2009 #1
    I learned from a website that cathode ray tubes fire electrons from an "electron gun" at the cathode towards the anode, hitting a piece of metal and produce cathode rays in the process.

    My question is; how do cathode tubes "shoot" electrons? Apparently it's due to a high potential difference between the anode and cathode, but wouldn't that create an arc of electricity instead?

    Also, why do the rays turn from blue to green when the electrons hit the piece of metal? I'm curious.
  2. jcsd
  3. Aug 16, 2009 #2


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    Science Advisor

    No, arcs occur because electrons moving through gas knock loose other electrons in the gas atoms, resulting in an ionized conductive path--once this happens, nearly unlimited currect can flow (this is the reason gas-dicharge lamps require current-limiting ballasts). In a CRT, there is a very hard vacuum so the electrons can travel from the gun to the screen virtually unimpeded.

    I don't know what you mean here. The colors in a CRT are produced from the electrons striking a phosphor; in a TV or computer monitor there are three which fluoresce either red, blue or green. Combinations of these colors produce nearly the whole range of human-visible colorspace.
    Last edited: Aug 17, 2009
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