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Fire - AND - Electric fields within matter

  1. Sep 27, 2010 #1
    I've been reading a section on induced dipoles in Griffiths,
    It says that although an atom as a whole is electrically neutral, there is a positively charged core and a negatively charged electron cloud, and when the atom is within an electric field the nucleus is pushed in the direction of the field and the electron cloud in the opposite direction. It also says that if the field is strong enough, it can pull the atom apart "Ionizing it"

    Somewhere (in highschool I think) I was told that fire is a highly ionized gas,

    So are electric fields produced by fire? simply by making something hot, like wood, by rubbing it against something to generate the temperature needed for the chemical reactions to take place surely doesn't create electric fields?

    I'm not sure, I'm just trying to understand what is actually going on inside fire IN PHYSICS TERMS, all the explanations of fire I can find on the internet are in terms of chemical reactions and such in CHEMISTRY TERMS, and do not exactly explain what is happening to the atoms.

  2. jcsd
  3. Sep 28, 2010 #2


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    While you can ionize atoms with strong electric fields, this is not the only way to ionize atoms. If a gas gets hot enough, then the atoms have enough energy so that the collisions between atoms are violent enough to knock the electrons loose, thereby ionizing them. This is a better description of what happens in a fire.
  4. Sep 28, 2010 #3
    Fire. Photosynthesis in reverse. It's all about atoms of carbon and atoms of oxygen getting awfully excited about being re-united back into carbon dioxide. There are several versions of this basic clip of Richard Feynman explaining it. You should understand that in this clip, Feynman is deliberately making it simple for laymen like me. But the basic point is well made.

  5. Sep 28, 2010 #4


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    However, I don't believe that your original statement, that "fire is highly ionized gas" is true. The molecules of a gas in fire are not necessarily ionized. In fact, I suspect that would be very unusual.
  6. Sep 28, 2010 #5


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    I think that a flame is a plasma - i.e. an ionized gas. However, it is typically not "highly ionized", meaning that the percentage of the atoms which are ionized is very small. Here is a reference, which shows the plasma of a flame being influenced by an E-Field.

    Last edited by a moderator: Apr 25, 2017
  7. Sep 28, 2010 #6


    Staff: Mentor

    The light given off by a flame is not the result of a plasma, it is the result of little bits of material (soot) getting very hot and glowing.

    Although there will be some ionization in the combustion products the degree of ionization is pretty low. Of course, exactly where you draw the line for how much ionization is required before you call something a plasma is a little ambiguous, so some people will call it a plasma and some will not. If it is a plasma it is barely a plasma and only exhibits the characteristic behaviors of a plasma very weakly.
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