h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

...and neither is mankind discovering how to use plasme right now. People have been messing about with fire for a long time.

I think the problem is that you cannot say that fire is a good example for plasma.

HELL

BTW: Electrons cannot be circling around the atomic nucleus...

Umm..

I'd imagine that the total mass of matter in a plasma state on (or immediately around) Earth is but a very very tiny fraction of the total mass of matter on/in/around the Earth - the overwhelmingly vast majority of which (by mass) is in a solid state.

So I'd say that plasma is very rare on Earth, as opposed to the Sun, which is (to all intents and purposes) entirely plasma (and has about 333000 times as much mass as the Earth).

jfmchivall

That's not the problem...

It is clear that the majority of our planet is NOT plasma. I was criticising the affirmation that FIRE is plasma.

And FIRE is not a really uncommon thing on this planet.

HELL

Flames can be plasma -- and since fire is essentially a chemical reaction, electrons play a large part in it. In particular, some electrons must become disassociated from their host atoms in order for any chemical reaction of the fire type to take place. So, fire is a good example. However, when you think of the size of the average hearth -- perhaps a cubic metre -- and then think of the amount of air vertically above that -- perhaps a hundred thousand metres -- and the amount of rock below -- six million metres -- you realize that even if the Earth's entire atmosphere were converted to plasma, this would be a far smaller quantity of matter than embodied as rock (even before you take density into account). As it is, fire is usually short-lived -- so it is fair to say it's uncommon by contrast with, say, tarmac, or animals.

Chemical reactions take place at the OUTER SHELL. Plasma is ALL electrons away from the nucleus. I think you are confusing things a bit.

Bye,

HELL

Actually, most "plasma" isn't. It takes a lot of energy to ionize to that extent -- yet the ionized gas in a fluorescent tube is usually considered a plasma, as is the ionized gas in plasma television screens. If this is a misuse of the term, fair enough, but in that case I and a lot of other people have been mistaught.

If you have been taught that plasma is ionized gas, then you have been mistaught. -- Then again maybe it's just me being to strict on definitions... In that case you wouldn't be allowed to: call plasma a state of matter, because then virtually everything (because ions are omnipresent and because everything is doing some chemistry) could be called a plasma...

Hmmmmmm....

HELL

I've always thought of plasma as being a gas which has been ionised to an extent where it can no longer be described accurately by the gas laws; that is, the electric and magnetic fields in the plasma affect its physical behaviour, so you get wierd things like Alfven waves and you can use magnetic confinement for example. Total ionisation of every atom is not necessary.

I'll see if I've still got my old notes from uni hidden in a box...

Here we are: from my final year course on Electromagnetic Radiation and Plasma Physics: "A plasma is any state of matter which contains sufficient free charged particles for its dynamical behaviour to be controlled by electromagnetic fields. On this definition it would encompass the solid state - metals and semiconductors - but usually it is concerned with ionized gases _in which the positive and negative charges are nearly balanced_ (Langmuir 1929)"
Irvine Langmuir was the early 20th Century physical chemist who apparently first used the term "plasma" in this context. (see http://www.xrefer.com/entry/218609 )

My lecture notes give examples as being: gas discharges, arcs [ie lightning], flames, thermonuclear reactions, the ionosphere, Van Allen belts, interplanetary space [solar wind is a plasma], aurora.

"A _very_ low degree of ionisation is sufficient for a gas to exhibit plasma properties... 1% ionisation : maximum conductivity [is reached]... Ionisation depends on temperature".

Hmmm... brings it all back... I slept through most of this course as the lectures were in a very hot, stuffy room at the end of the day. Must have learnt something although I've forgotten all the detail since. It was only 2 years ago!

There is an experiment which can be performed where a flame is placed in an electric field and separates ... we never did it at school but I remember the diagram from the book. I forget what it purported to prove.

I've certainly also seen spectacular induced current phenomena caused by placing a candle in a microwave. The candle flame became a mass of ball-lightning-like fizzing sparks, and buzzed loudly at fifty cycles.

I guess there are stricter definitions for 'plasma' nowadays, especially if one is talking about a 'state of matter'. Langmuir's definition might be a bit outdated but still widely used.

As I said, maybe I am being to strict on definitions... What the...

HELL

I think you can make a case for its behaviour being so radically different once a certain proportion of ions is attained that a seperate state makes sense. In any case, collective descriptions of things always break down at some point -- a biochemist friend of mine once told me that water is often composed mostly of what could be called ice crystals, but they are very small and not rigidly bonded. Effectively, all you need is for enough energy to be present to allow *some* molecules to slide past each other at any one point.

What abuot glass? Apparently that's technically a liquid. It certainly flows, over hundreds and hundreds of years ....

The problem with states is that there is a thing called the 'phase-law' (it has something to do with degrees of freedom and entropy). At the phase transition boundary all the energy is converted to transform the phase instead of heating stuff up (or cooling stuff down). For example: If you take a cup of water with ice in it and you cool it down you will reach 0°C, if you keep extracting energy from the cup of glass (and heat something elese up) the temperature will rise outside the cup, but inside the cup the temperature will stay constant (0°C nearly) until all water has transformed from liquid to solid, only then it will cool more. (Note that these boundaries are functions of pressure and concentration - so it is in fact possible to cool liquid water below 0°C, depending on the pressure you are using)

Or the other way round, when you boil water you reach 100°C, if you keep putting energy in, you will not heat the water more than 100°C until all water has evaporated.

With bose-einstein condensates and plasma it's basically the same, you have a phase-boundary somewhere. The PURE phase (and that's where I was being too strict) contains only plasma, and not a mixture.

With water... I think your biologist friend was oversimplifying somewhat. Water has a definite transition-point. Wtare though has the remarkable property to interact with itself. So, at some instances, especially when ou have confined water, or bound water, the structure 'resembles' ice a lot, even though it is liquid. This effect is also responsible for the anomalous behaviour of water. (i.e. that's why icebergs float)

The phase transition with glass is of another kind. Because of the intramolecular interactions the liquid gets so viscous that the energy cannot migrate as fast as in a 'normal' solid-liquid boundary. Here the boundary is somewhat 'smeared'. This transition is called the 'glass transition' (many compounds do have a more or less definite glass transition point, especially those used for liquid crystals - which can be considered to be another form of 'state'). Technically glass *could* be called a liquid with almost infinite viscosity. However, I would not dive into a pool full of that 'liquid'.

HELL

Ah, so water is a special case? That figures ....

I knew about phase transition boundaries, but didn't know such a boundary existed for gas-plasma -- although I suppose it must. Is is temperature-delimited in the same way, i.e. the gas temperature will not rise until total ionization is achieved?

Hmmm... dunno honestly, I have never seen a thermodynamic treatment of plasma, but then again why not? If it's a state there must be something to it, I guess? Then again maybe it's just another smeared 2nd order boundary... (Note: I am not talking aboput ionization potentials, I think ions and plasma should be kept in different drawers)

BTW... There are more of those so-called 'states': Liquid crystal, superfluid, superconductive... That's also one thing that made me go on that entry. Plasma is not the 'fourth' state... That enumeration is completely arbitrary, and IMHO confusing, it gives the impression that there's some 'mumbo-jumbo' going on about 'states'... (cf. that other thread where people went 'whoo' on ancient wisdom)

HELL

That's kind of why I was sceptical about the need to differentiate between completely and partially ionized particles -- many of these things are confused. I think you could argue that thixotropic fluids are another "kind" of state, superfluids are just plain weird ... all of these things are attempts to qualify differences between collections of atoms and molecules. Shouldn't there be an interstate between gas and plasma, where the gas is no longer molecular (if indeed it ever was) but is not completely ionized? I think that's a big enough qualitative difference to merit a "state change", potentially.