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Homework Help: Calculating the threshold ionization intensity for hydrogen gas.

  1. Jun 30, 2011 #1
    The problem statement, all variables and given/known data
    Calculate the threshold ionization intensity for hydrogen gas.

    The attempt at a solution

    The way I tried to work it out was to use the field intensity of air which breaks down at, 3x10^6V/m. The ionization potential of oxygen is 13.618ev, 14.534ev for nitrogen and 13.598ev for hydrogen. So I was thinking that the ionization potential of air would be around the same for hydrogen.

    Am I on the right track with this?
  2. jcsd
  3. Jul 1, 2011 #2
  4. Jul 3, 2011 #3


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    The problem is worded strangely. Gases have a threshold ionization energy (not intensity). In which case the threshold for hydrogen is the energy value you said for hydrogen -- the oxygen and nitrogen values are irrelevant.

    Did you type the problem statement exactly, word-for-word? And included all the given information?
  5. Jul 3, 2011 #4
    I wrote exactly what was in the question, and it's not possible to go check this as the academic year is over and school is closed.

    So the threshold ionization energy of hydrogen is 13.598ev right?

    One thing that I didn't write was that the answer should be in V/m.
    So I think that the answer for the question is just the dielectric strength of hydrogen which is 1.75x10^6 isn't it?

    The person who wrote the question probably messed up.
  6. Jul 3, 2011 #5


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    Okay, if they were really talking about dielectric strength ... I don't know how to calculate that, but it does depend on the gas density (or equivalently, pressure/temperature). Usually room temperature is assumed unless they say otherwise. But the pressure is unspecified, perhaps you are to assume 1 atmosphere? What class was this for?

    Presumably you were shown some way to calculate this at some point during your school term? And when they say to calculate it, I would expect that looking up (or knowing, from having memorized it) the value would not earn much credit for solving the problem.

    (Or, as you said, the person who wrote the question could have messed up.)
  7. Jul 5, 2011 #6
    You don't need to show the working out, our teacher likes to give his students a problem to solve where the answer isn't so obvious from a google search.

    For getting the right answer you get first pick of seats for the new year and our names get put into a raffle to win one of those space pens (however some of us think he's just going to give us a pencil).

    Is the 1.75x10^6V/m figure correct for hydrogen at room temperature and 1 atmosphere?
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