metalresearcher
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Maybe redundant topic, but is fire plasma ?
Some say NO, some YES.
Here a discussion on stackoverflow:
https://physics.stackexchange.com/questions/23469/is-fire-pl...
I say :
NO, because the temperature is too low, it is a pure chemical process.
YES, because when salts are in the fire, its spectrum shows emission lines, e.g. the bright yellow Na-D line. When putting copper salts or even
metallic Cu in the fire, flames will be colored green-blue.
What do you think ?
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unionised
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Since you can pass an electrical current through a flame, there's no way to dispute the fact that it's ionised, so it's a plasma.
On the other hand, it's a weak plasma- the degree of ionisation is low.
The yellow colour from sodium in a flame is due to neutral sodium atoms, rather than ions.
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Fantasma4500
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low density plasma, lets settle at that shall we. never really bothered to puzzle this one into place but i always knew fire and plasma was somehow
related
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unionised
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Why?
The density is a lot higher than that in a neon sign, for example.
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Fulmen
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There might be ionized atoms in a flame, but calling that plasma is like calling air for helium.
We're not banging rocks together here. We know how to put a man back together.
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rockyit98
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Nope! think of it as sea water. got some ions but mostly covalent molecules .and some free radicals here and there.
"A mind is a terrible thing to lose"-Meisner
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clearly_not_atara
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Instead of looking at specific questions like "is fire plasma?", physics as a discipline focuses on answers to questions like "how do I determine if a
sample is a plasma or a gas?". You will find a more orderly discussion here:
https://physics.stackexchange.com/questions/83658/is-there-a...
http://scienceline.ucsb.edu/getkey.php?key=3257
" A gas has zero conductivity, but when it turns into a plasma, its conductivity steadily grows but doesn't jump."
This is a little misleading: usually there is a point at which one of the derivatives of conductivity with respect to temperature, that is: (d/dT)^n
[S(T)] shows a singularity for some n. Also, sometimes plasmas do have a first-order phase transition, but it tends to be past the point at
which they start to ionized (the weakly-ionized to strongly-ionized first-order transition).
For a particular source you're interested in, the only way to know is to set it on fire and get a couple of electrodes and an ammeter 
The best example plasma for teaching is probably a glow discharge, because a: it is relatively common and b: it emphasizes the key measurable property
of plasma (conductivity)
https://en.wikipedia.org/wiki/Glow_discharge
[Edited on 28-1-2021 by clearly_not_atara]
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metalresearcher
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Glow discharge, is that not the same as a Corona discharge, appearing at high voltage power lines ?
In that case, the air close to the high voltage conductors, where the corona appears is also a plasma ?
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clearly_not_atara
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Yes, that is definitely a plasma.
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macckone
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It is partially ionized gas, aka plasma.
It isn't pure plasma, like in a sustained electric arc.
It is like asking if a slushy is a liquid or a solid.
Another example is fog or clouds, is it a liquid or a gas, in this case it is a suspension.
There should probably have its own name, I don't know ... like ... partially ionized gas.
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Morgan
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Tidbit
"St. Elmo's fire is a weather phenomenon in which luminous plasma is created by a corona discharge from a sharp or pointed object in a strong electric
field in the atmosphere (such as those generated by thunderstorms or created by a volcanic eruption)."
https://en.wikipedia.org/wiki/St._Elmo%27s_fire
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