Theoretical Maximum Positive Voltage

Thread Starter

Wendy

Joined Mar 24, 2008
23,415
Actually, my friend, you are wrong. Chemical plasma is still plasma.

http://en.wikipedia.org/wiki/Fire

This article claims there has to be a minimum temperature reached, but I don't agree. The glowing part of the flame is a plasma signature. Ever notice there are no cold flames?

http://en.wikipedia.org/wiki/Plasma_%28physics%29

http://en.wikipedia.org/wiki/Flame

http://www.plasma-universe.com/Image:Electric-candle-flame.jpg - I especially like this link.

http://www.plasma-universe.com/Fire_(flame)#Flames_as_plasma

We may have to agree to disagree with this one. It also appears there may be more exceptions than I once thought.
 
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magnet18

Joined Dec 22, 2010
1,227
You also claim it must be conductive. It most certainly is not.

I would have to look at the actual chemical mechanisms that show an ionization state for combustion before I would agree.

There are probably some flames that are plasma, but I doubt all of them are. I'm still pretty sure that it's excitation of electrons due to the temperature, but the electrons don't necessarily leave their atoms without being replaced (or at all), kinda like in an LED.

If I felt like it I could edit all the wiki links to say that, contrary to popular belief, a flame is not a plasma :p
 

Thread Starter

Wendy

Joined Mar 24, 2008
23,415
You also claim it must be conductive. It most certainly is not.

I would have to look at the actual chemical mechanisms that show an ionization state for combustion before I would agree.

There are probably some flames that are plasma, but I doubt all of them are. I'm still pretty sure that it's excitation of electrons due to the temperature, but the electrons don't necessarily leave their atoms without being replaced (or at all), kinda like in an LED.

If I felt like it I could edit all the wiki links to say that, contrary to popular belief, a flame is not a plasma :p
So you think the candle flame picture was doctored? I didn't just link to Wikipedia you know.
 

steveb

Joined Jul 3, 2008
2,436
... you can add all the electrons you like to the sphere and achieve all the negative voltage you want, I think. When it comes to removing electrons to achieve a positive voltage, is there a limit, and what would the limit be?
This thread asks a very interesting but difficult question. I would recommend posting this question over at Physics Forums. Even there, I think you will have trouble finding someone who can fully answer this question with certainty. But, you will get some good feedback I think.

As far as your comment above, you are homing in on the correct point of view. Ultimately the question comes down to, "how many protons or electrons can you group together and hold together?".

Holding charges together requires force. There are three forces that might achieve the job: gravity, electromagnetic force, or nuclear force.

Nuclear force is what holds nuclei together. It is by far the strongest force, but it is also a short range force. A quick look at the periodic table of elements tells you just how limited the nuclear force is in holding charges together. You can't even get 100 protons stuck together, even with neutrons added to form the nuclear glue.

Electrostatic force holds the atoms together in a solid, such as a metal. So, if you get a large enough chunk of neutral solid material together, you have a vehicle to hold some charges. A Van de Graaff generator shows us how to dump a large positive or negative charge onto a large conducting sphere and millions of volts can be generated this way.

A Van de Graaff generator in air is limited by corona discharge, but higher voltage is possible in vacuum. Still, eventually, I think the material will either expel electrons if too many electrons are present, or the material will explode if too few electrons are present. There will be a limit, and there are probably ways to estimate these limits.

But what about gravity? Although gravity is the weakest force (by far), one can use a very large chuck of mass to hold charges. You even alluded to this when talking about charges on the earth. However, even here there is a limit because electrostatic repulsive force between protons (or electrons) is far stronger than gravitational attraction between protons (or electrons). Hence, you need a lot of neutral mass present to hold large charges. Still, very large charge (and hence large voltage) can be generated by dumping more and more charge onto a planet or star etc. Ultimately, you may want to ask, "how much charge can be dumped into a black hole and held inside?". This is a question I've been trying to get an answer to myself and I still don't know the answer. Perhaps no one really knows the answer to this because there is (as yet) no accepted quantum theory of gravity, and such a theory may be needed to answer this question.

So, basically, I don't know how to find the limit, but I do suspect there is a limit. At the very least, we may decide to conclude that all the charges in the universe is limited. So, if we somehow separated all charges into a positive black hole and a negative black hole (forget about whether this is even possible), and placed them at opposite ends of the universe (forget about whether the universe even has ends) we have a maximum voltage given by this thought experiment. So the answer should not be "infinity".
 
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steveb

Joined Jul 3, 2008
2,436
I have another answer too.

Stealing the joke from Douglas Adams' "The Hitchhiker's Guide to the Galaxy", I'll say that I just calculated the maximum voltage to be 42. However, I'm still trying to figure out what the correct units are.
 

#12

Joined Nov 30, 2010
18,224
Very thoughtful answer (steveb) and within my ability to understand it. Thank you, and thanks to the other guys.

ps, this IS in the physics forum, isn't it?

I guess I'll get back to practical electronics. Plenty of n00bies waiting for us.
 

steveb

Joined Jul 3, 2008
2,436
ps, this IS in the physics forum, isn't it?
Yes, this is the physics forum here. However, there is another independent forum site called "Physics Forums". There you will find various forums for different fields of physics. Also, some high powered physicists are there, such as physics professors and other researchers. Some of those experts can give some real insight into questions like this.

Personally, I'd come here for electronics and circuit related topics. But, such a deep question is beyond the expertise of most of us here. You'll get some good feedback here, but over there you might stumble across a person doing research on this very question, or something closely related.

http://www.physicsforums.com/
 

magnet18

Joined Dec 22, 2010
1,227
So you think the candle flame picture was doctored? I didn't just link to Wikipedia you know.
The large voltages could be creating an ion wind, a piece of paper would probably have the same reaction. I know a plastic bag does.

If it is conductive it has a resistance greater than 2000 ohms per .1mm
 
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