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Homework Help: Pressure of a gas in discharge tube

  1. Aug 24, 2012 #1
    1. The problem statement, all variables and given/known data
    When the pressure of the gas in a discharge tube is gradually lowered
    I. There is a violet glow in the tube
    II. The glow in the tube split into bands which get further apart
    III. The glow and the bands eventually disappear and there is a green flourescence in the tube
    IV. The tube breaks into pieces.
    Which of the following are correct?
    A. I and II only B. I and III only C. I and IV only D. I, II and III only E. I, II, III and IV only
    I need explanation for your answers please! Any help will be so much appreciated. Thanks!

    2. Relevant equations

    3. The attempt at a solution
    In my own view, if a gas must conduct electricity, it must do so on some certian conditions. A gas in a discharge tube will only conduct electricity through it, if high voltage is applied at the two terminals of the tube and that must be done maintaining the pressure of the gas at a low pressure. The colour of the glow in the tube depends on the nature of the gas inside the tube.

    If the pressure of gas in the tube is continously lowered to the extent that there less molecule to ionize and cause flourecence in the tube,
    then the stated conditions such as:

    I. Violet glow in the tube
    II. Glow in the tube spliting into bands which get further apart
    III. Glow and the bands eventually disappearing and the emergence of green flourescence in the tube will be true.

    But I doubt the last possibility, that is the possibility of the tube breaking into pieces. Because judging from all the googling I made on the Internet, I found nothing supporting the last possiblity. What do you viewers think?
  2. jcsd
  3. Aug 24, 2012 #2


    User Avatar

    Staff: Mentor

    I think your answers are good. Here is more information about the discharge versus pressure -- it's called Paschen's Law (and the Paschen curve):


  4. Aug 24, 2012 #3
    Thanks for the compliment!
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