Electric arc in 0 gravity? Curved or straight?

AI Thread Summary
Electric arcs typically form a curved path due to the influence of gravity and the behavior of hot air, which rises because of its lower density. In a zero-gravity environment, the arc's shape may change to a straighter form, as convection effects would be eliminated. The arc's path is also influenced by electric field strength, gas density, and the type of gas involved, with higher voltages generally leading to more curvature. The discussion references Paschen's law, which explains the conditions under which arcs form, emphasizing that the arc seeks a path where ionization occurs more readily. Overall, the interaction of these factors determines whether the arc will be straight or curved.
kevin_tee
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I observe that electric arc forms a curve. I think that this is because electric arc is extremely hot and hot air goes up because it has less density. So if electric arc occur at 0 gravity would it be straight?
from wikipedia https://en.wikipedia.org/wiki/Electric_arc

Thank you.
 
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kevin_tee said:
I observe that electric arc forms a curve. I think that this is because electric arc is extremely hot and hot air goes up because it has less density.
No, it isn't.

When the arc passes through an airgap, it needs free charged particles ( ions/electrons ) to be created along the path. Having one particle created, the particle will be accelerated along the electric field, achieving velocity/energy. And if the achieved energy matches the energy needed to create a new free charged particle, at that instance the first particle hits a molecule, this will happen. So in turn, an avalanche/electric arc will be created.

So creation of an arc depends on:

  1. Electric field strength ( not too high, not too low )
  2. Density of gas ( distance between molecules, gas pressure )
  3. Sort of gas ( oxygen, hydrogen )
Now, say the electric field strength is too high, the arc must choose a path where along the field strength is weakened. At the same time it must follow the direction of the electric field. So if the difference in voltage is kept constant between "+" and "-" in the below figure, the arc must follow a longer/curved path. In this way, the field strength will be weakened. So if the applied voltage is close to the minimum voltage needed, the arc will be straight. With more voltage applied, the arc will be curved.

tVwsW.png


Some diagrams have been made, regarding gas, pressure, field strength. I think they are called something like "von Paschen curves" ( not sure ).
 
Hesch said:
I think they are called something like "von Paschen curves"
Well, here they are.
https://de.wikipedia.org/wiki/Paschen-Gesetz

( Sorry, could only find them in german )
 
Hesch said:
And if the achieved energy matches the energy needed to create a new free charged particle, at that instance the first particle hits a molecule, this will happen.
It does not have to happen, and there is no maximal energy. "Field strength too high" does not exist, a higher field strength makes arc production easier.
 
The effect of the Earth's magnetic field on the arc could be tested by changing the orientation of the arc 90 or 180 degrees.
 
kevin_tee said:
I observe that electric arc forms a curve. I think that this is because electric arc is extremely hot and hot air goes up because it has less density. So if electric arc occur at 0 gravity would it be straight?
from wikipedia https://en.wikipedia.org/wiki/Electric_arc

Thank you.

There is a flaw in your reasoning, because electrical breakdown also occurs in vacuum (i.e. in 10^-9 Torr or less). Here, there is very little "gas" and there is no such thing as "convection" (i.e. no viscous flow). The "arc" can take many shapes and forms.

Zz.
 
I think my question not well explain, The plasma arc I was talking about is plasma arc create by breakdown of air at atmospheric pressure, I observe that when high voltage arc across two electrodes, it form an electric arc that curve. Photo from wikipedia, as you can see it curve.

From what I see is that the electric arc curve upward, so it might do something with gravity.
More photo (google image serch: microwave oven transformer plasma)
http://cdn.instructables.com/FD5/CBF3/FQMXESGP/FD5CBF3FQMXESGP.MEDIUM.jpg
http://i.kinja-img.com/gawker-media/image/upload/s--ogJOK_qh--/1379227693472902437.gif
http://adammunich.com/wp-content/uploads/2011/04/xrast.png
 

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  • #10
OCR said:
A big one... :oldcool:

​

Yeah big one, but why?
 
  • #11
There is a 500,000 volt potential behind that very long arc. The switch you see opening here is "disconnect". It is normally opened only with no power to it. It has no arc quenching devices. In this case, a substation breaker probably failed in the closed position and they were forced to use the disconnect to cut the power. The hot ionized arc channel floated upwards until the potential could no longer sustain the arc and it then stopped. So, yes, under gravity, arcs generally curve upward. There are other forces involved, including the fact that a conductor repels any other current carrying conductor in which the current is traveling in the opposite direction. It will attract a segment in which the current is traveling in the same direction. All forces considered, a tortuous, sinuous shape develops.
 
  • #12
billslugg said:
There are other forces involved, including the fact that a conductor repels any other current carrying conductor in which the current is traveling in the opposite direction. It will attract a segment in which the current is traveling in the same direction. All forces considered, a tortuous, sinuous shape develops.
Can you please explain more of that, I don't really understand and it is kind of interesting.
 
  • #15
OCR said:
English...

https://en.wikipedia.org/wiki/Paschen's_law

Thank you.

mfb said:
"Field strength too high" does not exist, a higher field strength makes arc production easier.
The first paragraph under "Paschen curves" indicates that there is a field strength gap wherein the arc prefer to pass.

I think that if e.g. an electron passes an atom with too high velocity / too much energy, the electron will simply pass the atom without creating new free electrons. The energy must somehow match the limits of an energy gap.

That's why an arc searches for a path, where along the energy achieved between two atoms matches a certain (gapped) energy, depending on the sort of gas.

I agree that arcs ( e.g. Jacob's ladder ) not forms perfect curves. That is due to coincidences, ( which atom will be the next to be hit ). It's like birds flying in a flock: If the first bird turns, all birds will follow.
 
  • #16
Hesch said:
The first paragraph under "Paschen curves" indicates that there is a field strength gap wherein the arc prefer to pass.

Interesting stuff.

One also has glow discharge for example in a neon lamp. Paschen curves should be applicable for low pressure minimum voltage in these cases also where there is not an actual arc. The whole plasma will glow from electrons hitting the molecules and cause an avalanche of electron flow, "igniting" the whole plasma, with light given off as the molecules return to lower energy state from excited.
https://en.wikipedia.org/wiki/Glow_discharge

In an electrical discharge there are positive and negative species.
One aspect from the wiki is that,
free electrons at the cathode surface are created by the impacting ions
for the discharge to commence, and
each ionized atom leads to only one free electron
at the moment of discharge.

If the voltage across the gap is greater than that dictated by the Paschen curve, one would conclude that the above quotes cease to apply.
 
  • #17
Hesch said:
The first paragraph under "Paschen curves" indicates that there is a field strength gap wherein the arc prefer to pass.
I don't see how you could interpret the article like that.
For distances that are too small (compared to the mean free path length), you need an even stronger field to get enough ionization. That's what the article says: a higher field strength helps. So does a distance of the order of the mean free path length. There is no "field strength gap".
 
  • #18
mfb said:
I don't see how you could interpret the article like that.
For distances that are too small (compared to the mean free path length), you need an even stronger field to get enough ionization. That's what the article says: a higher field strength helps. So does a distance of the order of the mean free path length.
At a constant voltage, when the distance is too small, the field strength will bee too high. Hence the arc must choose a detour ( curved path ).

Field strength = ΔV / distance.

The discussion is not whether a higher voltage will create an arc or not, but whether the path of the arc will be straight or curved.
 
  • #19
Hesch said:
At a constant voltage, when the distance is too small, the field strength will bee too high.
No, the distance will be too short.
Keep the distance and increase the voltage and you get the arc even at a smaller distance.
Hesch said:
The discussion is not whether a higher voltage will create an arc or not, but whether the path of the arc will be straight or curved.
There are exotic cases where a curved arc is favored (electrodes and gaps of micrometers at atmospheric pressure), but those are not due to the field strength, but due to the longer distance, giving a higher chance of ionization.
 
  • #20
mfb said:
Keep the distance and increase the voltage and you get the arc even at a smaller distance.
That doesn't make sense to me.

Is the distance kept, or will it get even smaller ?

I say that if you have a constant distance between two electrodes, and that you at some voltage have a (nearly) straight arc between the electrodes, then if you increase the voltage, the arc will be curved, thereby increasing the length of the arc, so that the field strength = ΔV / (length of arc) ≈ constant.
 
  • #21
Hesch said:
Is the distance kept, or will it get even smaller ?
The distance is set, I don't understand what "will it get even smaller" means.
Hesch said:
I say that if you have a constant distance between two electrodes, and that you at some voltage have a (nearly) straight arc between the electrodes, then if you increase the voltage, the arc will be curved
That is wrong, and I don't see where you would get that from.
 
  • #22
mfb said:
I don't understand what "will it get even smaller" means.
In #19 you wrote:

Keep the distance and increase the voltage and you get the arc even at a smaller distance.

mfb said:
That is wrong, and I don't see where you would get that from.
"That is wrong" is not a reasonable argument. How do you think the arc will be ignited?

I get it from the first paragraph under "Paschen curves", link: https://en.wikipedia.org/wiki/Paschen's_law
 
  • #23
Keep the distance and increase the voltage and you get the arc even at a smaller distance.
That is correct. What is unclear about it?
You can have an arc at a given distance, then you reduce the distance, and the arc disappears. Now increase the voltage, and you get an arc again.
Hesch said:
That is wrong" is not a reasonable argument.
See the previous posts, see the Wikipedia article, see the references given there. You make an unsourced claim. You have to find a reference for it.
Hesch said:
I get it from the first paragraph under "Paschen curves", link: https://en.wikipedia.org/wiki/Paschen's_law
Which is in clear contradiction to what you claim here.
 
  • #24
mfb said:
Which is in clear contradiction to what you claim here.

It says:

Early vacuum experimenters found a rather surprising behavior. An arc would sometimes take place in a long irregular path rather than at the minimum distance between the electrodes.

Like e.g. "Jacob's ladder" or lightning in a thunderstorm.
 
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  • #25
For reasons I explained here. Distance too short.

Lightning in a thunderstorm is an entirely different topic, and has different mechanisms.
 
  • #26
mfb said:
Lightning in a thunderstorm is an entirely different topic, and has different mechanisms.
Why is it a different topic?

Which different mechanism?
 
  • #27
Start a new topic if you want to discuss lightning, please.
 
  • #28
mfb said:
Start a new topic if you want to discuss lightning, please.
I think it will be the same discussion: Hot air, magnetic field influence, Paschen's law and Jacob's ladder.
Would you find the title "Long electric arc in 0 gravity? Curved or straight?" suitable ?
 
  • #29
Hesch said:
Thank you.
You're welcome... :oldsmile:
 
  • #30
kevin_tee said:
I observe that electric arc forms a curve. I think that this is because electric arc is extremely hot and hot air goes up because it has less density. So if electric arc occur at 0 gravity would it be straight?
from wikipedia https://en.wikipedia.org/wiki/Electric_arc

Thank you.

I suggest that at 0 gravity, "up" would be inconsequential or for the purpose of your question, every direction would be up.
 
  • #31
The shape of arcs may be influenced by the relative alignment of the faces of the two electrodes .

Electrode faces which are both angled up do seem to produce upward curved arcs .

220px-Lichtbogen_3000_Volt.jpg
 
  • #32
Nidum said:
The shape of arcs may be influenced by the relative alignment of the faces of the two electrodes .
Did You see arc curving down? The heated air in the plasma rises up and the least resistance between electrodes remains through the plasma arc.
 
  • #33
kevin_tee said:
Yeah big one, but why?
Very long arc is shaped at air movement and the least resistance between electrodes remains through the plasma arc.
 

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