Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Gas conduct electricity?

  1. Dec 5, 2006 #1
    Can gases of atoms (or very loosely bounded atoms) conduct electricity?
  2. jcsd
  3. Dec 5, 2006 #2
    If the potential across the gas is high enough it will spontaneously ionise a path and a current will flow, if only for a short time till the potential difference drops below ionisation levels.

    This is essentially what causes lightning.
  4. Dec 5, 2006 #3
    A gas is the same as any other insulator. Given enough potential the gas will break down. The break down strength of air is approximately (Correct me if I'm out by a factor of 10) 1kV/mm.
    Different gases ionise at different potentials and also relax at different rates. There for something like SulphurHexaFlouride that is used in HV switch gear needs a lot of electrical stress to break down but recombines very slowly after the breakdown.
    Nitrogen on the other hand breaks at a lower stress but recombines quite quickly so it is used in spark gap switches for Marx Generators.
    This is something to note with HV systems that if they are on fire it is not necessarily a good idea to use CO2 to try and put it out.
    The really big advantage of compressible gases is that the breakdown voltage is proportional to the number of Mols of gas between the conductors, so in a fixed volume spark gap you can vary the breakdown voltage by changing the gas pressure.
  5. Dec 5, 2006 #4


    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor

    The problem here is that the question (and the scenario that is relevant) is very terse, making it rather vague to provide a specific answer.

    For example, we all know that a plasma can conduct electricity. Well, when we have breakdown or ionization, that is essentially what we get first - a plasma! But the knowledge that a plasma can conduct is obvious. So is this what is being asked in the OP?

    If not, then talking about breakdown and ionization of gasses in high fields is irrelevant.

    Which leaves me wanting to know if a neutral gas can conduct electricity and why it is being asked.

  6. Dec 5, 2006 #5
    I wasn't thinking about ionized gas but electrically neutral gas of covalently bonded molecules, ionicly bonded compounds and pure metallic substances. Can any of the three in gas form conduct electricity?
  7. Dec 5, 2006 #6


    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor

    There has to be something that is causing this question. I mean, a NEUTRAL particle, by definition, already says all that needs to be said. Even a neutral polar particle/molecule where one can induce an electric dipole would still not conduct anything.

    So unless there's something beyond this, the answer is no.

  8. Dec 6, 2006 #7
    I am thinking of neutral particles only.

    A neutral metallic substance in solid or liquid form can conduct electricity because of their valence electrons.

    A neutral ionic substance in liquid form can conduct electricity through the movement of the ions but not as a solid.

    A neutral molecular substance cannot conduct electricity in solid nor liquid form.

    In case you're wondering, these information are from a chemistry textbook but there is no mention of these substances in gas form. Would the gas form of any of the three substances conduct electricity if so which ones?

    I have a feeling that when the metallic and ionic substances are in gas form, they are not connected so the particles will no longer be together and any conduction will mean they will have to break apart hence be ionized which would no longer be a neutral situation anymore.

    With the molecular substance, the stronger intermolecular attraction would be dipole-dipole but if they are not strong enough to influence the solid or liquid state then how could it affect the gas state?

    So I have a feeling the answer to the original question is no. Correct?
    Last edited: Dec 6, 2006
  9. Dec 6, 2006 #8


    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor

    But both of these are NOT the same as "neutral gas particles". In metals, the behavior of the metal is NOT due to individual atoms of the metal. The atoms have lots their individual identity and form a COLLECTIVE many-body system which forms the conduction band. The comparision between the two isn't valid.

    I have already given you the answer.

  10. Dec 6, 2006 #9
    you're kind of asking can something conduct after ruling out the mechanism by which conduction happens.

    you could i suppose fire electrons or other charged particles through a gas, but though this is current it isn't conduction
  11. Dec 6, 2006 #10
    "Electrical conduction is the movement of electrically charged particles through a transmission medium."

    So why do you say "...though this is current it isn't conduction"
  12. Dec 6, 2006 #11
    So metals and ionic compounds in gas form will be drastically different to their liquid and solid forms? What will be some of their properties? One thing is that the ionic compound in gas form will be like neutral molecules hence lose their ability to conduct electricity. Unless a strong electric field is applied and rips their ionic bond.
  13. Dec 7, 2006 #12
    because if you're just firing charged particles through a gas, which we've somehow forbidden from being ionized, then the gas isn't acting as a transmission medium
    Last edited: Dec 7, 2006
  14. Dec 7, 2006 #13
    what is forbidden from being ionized? You mean the gas? So you are saying the gas in this case would not be doing anything and so not performing the conduction.
    Last edited: Dec 7, 2006
  15. Dec 7, 2006 #14
    oh god, don't you read your own posts? i'll remind you

    but even if you don't how could my "...gas, which we've somehow forbidden from being ionized..." mean anything but the gas, sheesh

    maybe english isn't your first language

    well you've not allowed it to be ionised, so it wouldn't be able to conduct, it could i suppose scatter, but you've set things to be so far from reality that it is pointless to speculate

    i'm unsubscribing. too trollish
    Last edited: Dec 7, 2006
  16. Dec 7, 2006 #15
    It can be hard to understand others on forums espcially if the sentences are long and doesn't begin with a capital letter nor end with a punctuation mark. And both the writer and reader doesn't spend a lot of time on what they're doing.

    But anyway thanks for your input and others in this thread. I have come to realise that the answer is no unless the particle is ionized.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook