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How fast do CRTs shoot electrons?

  1. Jan 19, 2012 #1
  2. jcsd
  3. Jan 19, 2012 #2
    It must be less than the speed of light.
  4. Jan 19, 2012 #3
    Yes I know that because electrons have mass and therefore (according to special relativity) they cannot reach light speed. But that wasn't the question, the question was HOW FAST do CRTs shoot electrons (on average)?
  5. Jan 19, 2012 #4


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    With a quick bit of googling I found that the voltage of a CRT TV cathode is 400 V. Therefore an electron accelerated will obtain 400 eV of energy. The speed of an 400 eV electron is 1.18*10^7 m/s or ~4% of the speed of light.
  6. Jan 19, 2012 #5


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    In a large tube-TV the accelerating voltage the electron feels is about 25,000 Volts, so a rough non-relativistic approximation says that will be about 1/3 the speed of light.

  7. Jan 19, 2012 #6


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    Oops, dunno how I came up with 400 V. Maybe that's for a ye olde oscilloscope or something.
  8. Jan 19, 2012 #7
    Haha it's grand, thanks all.
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