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Daylon
01-17-2003, 02:21 AM
You know..the little blue arc that shocks the hell outta ya and causes people to pull an orange robe buddhist at the gas station?

Why doesn't it burn ya? Too short a timeframe? I'm thinking it's gotta be a couple thousand degrees...

??

Thanks in advance.

engineer_comp_geek
01-17-2003, 11:24 AM
It's an electric arc, not a flame. When something resists the flow of electric current (which pretty much everything except for superconductors do) then the energy gets converted into heat. The flow of electricity in a shock like that is too short and contains too little energy to heat up things noticably. A lightning bolt, on the other hand, is exactly the same thing on a much bigger scale. Most of the damage done to people by a lightning bolt is burn damage, and many forest fires and brush fires are started as a result of a lighning strike every year.

Electric arcs like what you describe are typically a discharge of several thousand volts (probably between 10,000 and 80,000 volts if you can see the spark) but very low current. Your stove cooks with a much lower voltage, but a much higher current. Much more energy gets transferred to the heating element because of this. Lightning is several million volts with several hundred thousand amps of current, which is so much energy that it can cook darn near anything despite being such a short duration.

Your fingers do get heated up slightly during a static discharge, but not enough to really be noticable. The pain comes from your nerve's responses to the electricity flowing directly down through your nervous system.

Coffeeguy
01-17-2003, 12:01 PM
That. Is. So. Cool.

Daylon
01-17-2003, 03:52 PM
Yeah.....but WHAT"S THE TEMPRATURE.... you just said it's converted to heat? How hot is a spark?

ultrafilter
01-17-2003, 04:32 PM
Originally posted by Daylon
Yeah.....but WHAT"S THE TEMPRATURE.... you just said it's converted to heat? How hot is a spark?

It's only converted to heat in the presence of high resistance, which you don't have. The spark that makes you jump doesn't really have a temperature.

ultrafilter
01-17-2003, 04:33 PM
Perhaps a clarification is in order.

The temperature of an object is essentially a measure of the average kinetic energy of its molecules. A spark contains no molecules, and therefore has no temperature.

World Eater
01-17-2003, 04:38 PM
Orange robe buddhist?

:confused:

What is this?

Derleth
01-17-2003, 04:46 PM
He's referring to the wild dancing performed by some Buddhist sects and the Hare Krishnas (which may or may not be Buddhist, I don't know).

Splanky
01-17-2003, 04:52 PM
He's probably referring to the famous picture of a monk who burned himself alive at a gas station in protest of something or other.

I think the picture is on the first RHCP CD (or this is another flaming monk)

http://southwestern.edu/~bednarb/su_netWorks/projects/hobock/monk.jpg

Splanky
01-17-2003, 04:54 PM
That would be RATM (Rage Against the Machine) not RHCP (Red Hot Chili Peppers). I feel so stupid.

TheeGrumpy
01-17-2003, 04:56 PM
Along the same lines...

Is the tiny "crackle" associated with a spark just a miniature thunderclap? If it is, that suggests that the air is heated for a moment, causing a small "boom."

Splanky
01-17-2003, 05:03 PM
http://gradcat.com/vietnam/immolation1.jpg

This is the most well known shot of the incident, with the gasoline canister next to him and the car in the background.

Daylon
01-17-2003, 05:06 PM
A spark contains no molecules, granted...it's a shifting of electrons... are you saying that electrons in a spark have no temperature?

Does the energy only get converted to light then? Not temperature?

Right, by orange robed buddhist, I was referring to the recent spate of news articles where people have blown themselves up accidentally by static discharge while filling up their cars at gas stations...

Splanky has the right pic I was referring to.

Whack-a-Mole
01-17-2003, 05:26 PM
I don't know about a spark but they have certainly measured the temperature of lightning which averages around 30,000 K (http://hypertextbook.com/facts/1999/DavidFriedman.shtml) (or about 53,000 F).

Given that lightning and sparks are essentially the same thing just on different scales I would assume sparks have a temperature as well.

Whack-a-Mole
01-17-2003, 05:30 PM
Ok...getting closer here...

The temperature of a spark in a spark plug is around 800-900o C. (Cite: http://sciencenet.org.uk/database/Technology/9609/t00171d.html )

I'll grant that a spark from a spark plug is a lot juicier than what you get off your light switch after shuffling over the carpet but I can't find a cite for a 'normal' spark (yet).

Daylon
01-17-2003, 07:02 PM
At 900 to 900 degrees centrigrade, is that considered plasma? Are sparks just itty bitty bits o plasma then?

SUperheated gas, ionized electrons = plasma right? Is that what makes the light?

Soo....right now we we figure it's somewhere between 0 and 53,000 F.

;-)

D.

bbeaty
01-17-2003, 07:36 PM
A spark contains no molecules, and therefore has no temperature.

A spark is not "electricity", instead it is composed of nitrogen and oxygen molecules which have turned into plasma. You can't have sparks in vacuum, vacuum is a perfect insulator.

I've looked at my skin under a microscope after zapping myself with "static" sparks. The spark produces a tiny white spot on the skin. It's probably a burn mark, since skin has fairly high resistance, and the value of electric current during the spark is fairly immense. Also, the resistance of the white spot is lower than the surrounding skin, so once a spark has made its mark, later sparks will tend to "jump" to that same spot on your finger.


Spark temperature is more than enough to ignite flammable vapors. If your house has an electric stove, you might not know that modern gas stoves don't have "pilot light" flames, instead the gas burners are ignited with a high voltage spark generator.

Desmostylus
01-17-2003, 08:08 PM
Originally posted by bbeaty
You can't have sparks in vacuum, vacuum is a perfect insulator.Vacuum isn't a perfect insulator. You can quite easily get current to flow through a vacuum, but you would call it an electron beam or a pseudospark, rather than a spark.

Speaker for the Dead
01-17-2003, 08:16 PM
What would an electron beam/pseudospark look like?

Desmostylus
01-17-2003, 08:47 PM
An electron beam doesn't look very interesting. No photons are involved, so you can't see it.

The CRT in a computer monitor uses an electron beam. Nothing visually interesting happens until the electrons hit the phosphors on the screen.

bbeaty
01-17-2003, 09:13 PM
Originally posted by Desmostylus
Vacuum isn't a perfect insulator. You can quite easily get current to flow through a vacuum, but you would call it an electron beam or a pseudospark, rather than a spark.

But that's cheating. If a region of space contains electrons (or ions, or any other sort of charged particles,) THEN IT ISN'T A VACUUM ANYMORE. :)

I could also "prove" that water is a good conductor, all I have to do is dump salt into it. But that says nothing about the conductivity of PURE water.

A perfect vacuum is a perfect insulator, since there are no charge carriers present. Yes, electrodes can contaminate a vacuum, and once some ions or electrons have been injected, then a voltage will cause a current. But the electron cloud surrounding a hot filament in a vacuum tube is not "a vacuum."


Side issue: lightning is impossible in a vacuum since lightning is the electrical breakdown of a gas. If you place a huge e-field across a gas, the gas turns to plasma and you'll get an outbreak of glowing streamers. If you place a huge e-field across a vacuum, nothing happens since there are no gas molecules present which could ionize.

Desmostylus
01-17-2003, 09:35 PM
Originally posted by bbeaty
But that's cheating. If a region of space contains electrons (or ions, or any other sort of charged particles,) THEN IT ISN'T A VACUUM ANYMORE. :)
Forgive me if I don't accept your argument. Defining a vacuum as something that can't have an electron in it and then claiming that a vacuum is a perfect insulator is not a useful representation of how things work.

You could also claim that light can travel through glass, but not a vacuum, because once there are photons in it, it isn't a vacuum anymore.

engineer_comp_geek
01-17-2003, 10:15 PM
The electric discharge doesn't heat you because it's hot. The electric discharge heats you because there is electricity flowing through something that resists the current (your body). The heat that gets transferred to you is not generated in the spark, but rather in your tissues.

The air gets heated along the way too, and some of the oxygen gets converted to ozone. In fact, it's the rapid expansion and contraction of air due to the heating that makes the "zap" sound (or the thunderclap on the larger scale of lightning). None of this heat gets transferred to you however.

If you want to know the temperature that the air gets heated to as the electrons move through it, it's pretty darn hot (I don't know the exact numbers so I'll just go by what the others have posted). If you want to know the heat that gets to you from the spark it's pretty much nothing. If you were a superconductor you wouldn't generate any heat from the electricity flowing through you. Since you are not a superconductor, as the electricity flows through you, it generates heat, a small amount of heat in the case of a little spark, a rather substantial amount of heat in the case of a lightning bolt.

There's two bits of heat here. (1) The spark heats the air and (2) the electricity (not really a spark at this point) heats your tissues as it goes through them.

Does that answer the OP?

bbeaty
01-17-2003, 10:51 PM
(hijack!)

Forgive me if I don't accept your argument. Defining a vacuum as something that can't have an electron in it and then claiming that a vacuum is a perfect insulator is not a useful representation of how things work.

I have to strongly disagree. "How things work" for conductors is based on charge density and mobility. Injecting electrons into a vacuum CONVERTS IT INTO a conductor. (Just as dumping salt into pure water converts it into a conductor, just as triggering the formation of spark-plasma will convert air into a conductor.)

Measure a vacuum with an ohmmeter. It says infinite ohms. Do the same thing with air, or with pure water. These are insulators. Just because we're able to convert them into conductors does not mean they were conductors BEFORE we futzed with them.



You could also claim that light can travel through glass, but not a vacuum, because once there are photons in it, it isn't a vacuum anymore.


I'm not trying to be twisted. Our disagreement hinges on the defintion of "electrical conductor." There are two different definitions in common use:

1. "something through which electric charges can pass" (based on the incorrect "empty pipes" analogy for electric circuits)

2. "something which contains mobile charges" (based on Ohm's law)

So according to #1, a vacuum is a conductor because it doesn't stop electrons from flowing. But according to defintion #2, a vacuum is an insulator because it doesn't contain any movable charges. Which definition is correct? A physicist would go for #2 : Put a voltage across something, and if there is no current, then there must be no mobile charges available. Measure a vacuum with an ohmmeter, the meter will say infinite ohms.

A metal wire is nothing like an optical fiber, since wires are "pre-filled" with the material which flows and optical fibers are not. Wires aren't transparent to electrons. Instead, wires are like water hoses which are already filled with water. If an optical fiber was like a wire, then the fiber would have to be full of unmoving photons all the time, and in order to transmit light, you'd have to apply some kind of pressure across the ends of the fiber, and only then would the light inside begin to move.

To create a current in a wire we just have to apply a voltage across it's ends, and then the wire's own electrons will start flowing. To create a current in a vacuum we FIRST have to convert the vacuum into a conductor by injecting mobile charge carriers. Only then can we create a current by applying a voltage across the vacuum. The injected electrons have changed the conductivity of the vacuum.

Desmostylus
01-17-2003, 11:16 PM
I just think that the statement "vacuum is a perfect insulator" is silly. Even if you eliminate conduction currents, there are still displacement currents to worry about.

You have to very narrowly define "vacuum", "perfect" and "insulator" to make the statement true.

That makes the statement pretty much useless, unless you provide all of the qualifications that make the statement true.

scr4
01-17-2003, 11:56 PM
Originally posted by Desmostylus
I just think that the statement "vacuum is a perfect insulator" is silly. Even if you eliminate conduction currents, there are still displacement currents to worry about.
No insulator blocks displacement currents, so it's a bit of a stretch to call something a conductor on that basis.

I do agree that "vacuum" needs to be better defined. A laboratory "vacuum" of 10-3 torr pressure is a very good conductor; a 500-volt power supply can easily push current through it. A high-grade vacuum under 10-6 torr is, for most intents and purposes, a very good insulator. It's safe to apply thousands of volts on a bare wire and rely on the vacuum to act as insulation. To push electrical current through a high-grade vacuum requires not only a high voltage, but a method of supplying free electrons such as a heated filament.

Desmostylus
01-18-2003, 12:25 AM
Originally posted by scr4
No insulator blocks displacement currents, so it's a bit of a stretch to call something a conductor on that basis.You are using a narrow definition of insulator. Your own statement implies that currents can pass through insulators. If I said to you something like "the signal current passes through the input capacitor to the op-amp", you probably wouldn't respond with "wait a minute, a capacitor is an insulator". Maxwell's version of Ampere's law makes no particular distinction between the conduction component and the displacement component.

Originally posted by scr4
To push electrical current through a high-grade vacuum requires not only a high voltage, but a method of supplying free electrons such as a heated filament. No heated filament is required. The corona effect occurs.

scr4
01-18-2003, 01:12 AM
Originally posted by Desmostylus
You are using a narrow definition of insulator. Your own statement implies that currents can pass through insulators.
True, AC current can pass through an insulator. Is that a problem? In all the references I've seen, an insulator is defined as something with a high resistance. Not impedance, but DC resistance.

No heated filament is required. The corona effect occurs.
I thought "corona effect" refers to electrical conduction by ionized air molecules. If you have cold electrodes in high-grade vacuum and apply high voltage, how exactly are ions generated? And what kind of voltages are you talking about? I've used several thousand volts in 10-6 torr vacuum chambers successfully (i.e. without accidental discharges). I admit I've never looked into what happens if you use 10,000 volts.

Desmostylus
01-18-2003, 01:34 AM
Originally posted by scr4
True, AC current can pass through an insulator. Is that a problem?Do you see why the statement "vacuum is a perfect insulator" isn't a great one?

If you mean by "insulator" something with high resistivity, then okay. If you interpret "insulator" as meaning that current can't pass through it, then it requires further explanation.

Originally posted by scr4
I thought "corona effect" refers to electrical conduction by ionized air molecules. If you have cold electrodes in high-grade vacuum and apply high voltage, how exactly are ions generated?You don't need ions. Electrons get stripped directly from the conductor.

You can't just state that vacuum is a perfect insulator, without explaining all of the assumptions behind the statement. That is, that "vacuum" precludes the existence of electrons, that "insulator" refers only to resistivity and not to the conduction of current, or that the existence of time varying electric fields is precluded, and that "perfect" isn't meant to refer to breakdown voltage or dielectric constant, etc.

Daylon
01-18-2003, 01:42 AM
Damn..you start out with 'how hot is a spark' and you get treatises on vacuum efficiency...

So how hot is it? LIttle bit o plasma, then the reaction to your skin is negligble because the short duration that the heat is applied isn't enough to damage anything...

So far we have:

1) Static electricity sparks super heat the air, generating the 'pop'
2) it hurts more due to direct electricity to the nerves rather than heat
3) it's somewhere between 0 and 53,000F.

Soooo...back to my original question... HOW HOT IS A SPARK? (static electricity, socks on a shag carpet kinda spark)

???

D.

scr4
01-18-2003, 01:52 AM
You don't need ions. Electrons get stripped directly from the conductor.
So what is the field strength or voltage required to do this? If it's true I'd like to know; I've never worried about this when conducting experiments in vacuum.

scr4
01-18-2003, 02:10 AM
Originally posted by scr4
So what is the field strength or voltage required to do this? If it's true I'd like to know; I've never worried about this when conducting experiments in vacuum.
Sorry, I shouldn't have said that. Yes, I realize it does happen, but only under extreme conditions. Something on the order of 200 kilovolts for a 1-mm gap.

engineer_comp_geek
01-18-2003, 02:59 AM
Originally posted by Daylon
So how hot is it? LIttle bit o plasma, then the reaction to your skin is negligble because the short duration that the heat is applied isn't enough to damage anything...

So far we have:

1) Static electricity sparks super heat the air, generating the 'pop'
2) it hurts more due to direct electricity to the nerves rather than heat
3) it's somewhere between 0 and 53,000F.

Soooo...back to my original question... HOW HOT IS A SPARK? (static electricity, socks on a shag carpet kinda spark)

???

D.

The answer to your question, with respect to the heat applied to your skin (which seems to be what you keep asking) is that it is not hot at all. There is no heat transferred from the spark to your skin.

The temperature of the air is going to vary, since the spark can range from what you can feel but doesn't even cause a visible spark, up to holy cow what a big blue bolt that was. At the bottom end you're not going to get much above room temperature. At the top end it will be pretty close to that of a spark plug, which someone else posted was in the range of about 800 deg C. I poked around on google trying to find the temperature at which you actually start to see the blue light but wasn't very successful.

You seem to keep asking for the heat that would be transferred to your skin, and the energy being transferred to your skin is not in the form of heat.

You keep saying things along the line of "the heat is applied..." There is no heat applied to your skin. The answer to the way you keep wording the question is the spark has no heat. It's kind of like asking how much heat is in a 120 volt wall socket. There's lots of energy there, but it's not in the form of heat.

Daylon
01-18-2003, 03:01 AM
Nope..not asking in terms of heat applied to skin.

More specifically I think i'm asking "what is the temperature of a static electric spark such that you can see the visible blue flash with the naked eye"

?

D.

Mr. Skinny
01-18-2003, 08:10 AM
Daylon, If I had seen your thread yesterday I could have got an expert answer for you quickly. We have an Electrostatic Discharge Laboratory where I work, and I'm sure they can answer your question.

Unfortunately, I will be out of town next week, and unable to pose your question to them.

If you can wait about 10 days, I'd be glad to get an answer for you.

I'll check this thread when I get back to the office. Maybe I can have an answer for you on the 27th or 28th.

Daylon
01-22-2003, 06:48 AM
In the mean time - anyone else know?

Cartooniverse
01-22-2003, 07:06 AM
Originally posted by ultrafilter
Perhaps a clarification is in order.

The temperature of an object is essentially a measure of the average kinetic energy of its molecules. A spark contains no molecules, and therefore has no temperature.

A lightning bolt contains no molecules either, and it's difficult to convince me that a lightning bold has no temperature. Can that be?

Can it be that burns caused by lightning strikes are not from the bolt itself, but from the effect of frighteningly high voltage passing through objects ( trees, cows, people ) whose bodies provide resistance, and therefore generate heat in the resistance of that voltage?

Cartooniverse

Firewall
09-28-2011, 07:20 AM
I don't get this. Lightning contains air molecules heated to high temperature as do electrical sparks in the atmosphere..as far as I know.

Am I wrong?

Saint Cad
09-28-2011, 08:23 AM
Mr. Skinny is out of town longer then he predicted.

Machine Elf
09-28-2011, 10:26 AM
Nope..not asking in terms of heat applied to skin.

More specifically I think i'm asking "what is the temperature of a static electric spark such that you can see the visible blue flash with the naked eye"

?

D.

It's pretty hot, and in fact it may move a lot of current. Peak temperatures, as noted upthread, may be on the order of 50,000F, and peak current may be tens of amps. However, the duration of high current is on the order of nanoseconds, and the total mass of the air that is heated to 50,000F is very, very small, so there's not a lot of energy contained in the spark gap.

Telemark
09-28-2011, 10:38 AM
Just a reminder, this thread is 8 years old.

Chronos
09-28-2011, 11:23 AM
It's got the wrong answer, though. A static shock hurts precisely because it burns-- The current itself won't hurt you at all. If you suspect you'll get a static shock from a doorknob or whatever, you can take a key or coin or something out of your pocket, and use that to touch the doorknob. You'll still get the full current through your finger, but since the hot spark is in contact with the key, not your finger, it won't hurt.

TriPolar
09-28-2011, 11:58 AM
I don't get this. Lightning contains air molecules heated to high temperature as do electrical sparks in the atmosphere..as far as I know.

Am I wrong?

Lightning is air molecules forming a plasma. Plasmas can have a wide range of temperatures, and I think air plasmas are pretty hot, but this is an unusual case of a plasma created by very high voltage and direct current. Sparks are basically the same thing. But what you feel temperature-wise from touching a spark is the heat generated by the current meeting resistance in your body. It is no longer a plasma as it enters your body. I suppose with enough energy your body could become a plasma too, but you would cease caring about temperature, and everything else at that point.

naita
09-28-2011, 12:28 PM
It's got the wrong answer, though. A static shock hurts precisely because it burns-- The current itself won't hurt you at all. If you suspect you'll get a static shock from a doorknob or whatever, you can take a key or coin or something out of your pocket, and use that to touch the doorknob. You'll still get the full current through your finger, but since the hot spark is in contact with the key, not your finger, it won't hurt.

Using a key also means the current is conducted into your body over a larger area, so I can't agree it's proof at all that it's the heat, not the current, that causes the pain.

Since you can't really separate the high localised current from the heating of the point of entry there's not really any way to know, except physiological expertise, or measuring the temperature increase at the point of entry.

Also "the hot spark" would be unlikely to be the cause of the pain, it's a tiny volume of hot gas, and gas contains very little energy. If it's temperature that causes the pain I'd expect it to be the direct heating of tissue at the point of entry where the current is concentrated in a tiny area.

ZenBeam
09-28-2011, 05:42 PM
During winter, at work I use a key to avoid getting shocked. A lot of the charge collects on the key relatively slowly before the spark, so the total current out of my fingers during the spark is smaller, in addition to being over a larger area.

It doesn't hurt, but I can still feel it. So I suspect it is the current, not the heat, that hurts.

Mr. Skinny
09-28-2011, 06:17 PM
Mr. Skinny is out of town longer then he predicted.
I entirely forgot about this thread (if that's not obvious). I still work in the same place though and the ESD lab is still next door.

*Skinny writes himself a note*

Firewall
09-29-2011, 12:11 PM
Thanks folks
So this business about a spark not having a temperature (cause it supposidly contains no molecules) is wrong...Right?

TriPolar
09-29-2011, 12:30 PM
Thanks folks
So this business about a spark not having a temperature (cause it supposidly contains no molecules) is wrong...Right?

I disagree. A spark could be considered the voltage, the current, the molecules in a plasma state, the light emitted from the plasma, or any combination of those. The question isn't that clear.

dracoi
09-29-2011, 06:19 PM
I disagree. A spark could be considered the voltage, the current, the molecules in a plasma state, the light emitted from the plasma, or any combination of those. The question isn't that clear.

Well, I disagree with you. :)

Seriously, a spark is a spark. I get that there are components of a spark, that these components may be different temperatures and that temperature may even be irrelevant for some components or some sparks.

But we're not the Nobel committee and we're not drafting legislation. Surely, we can read between the lines to find a way to reasonably answer "What's the temp of a static charge spark?"

(Especially after 8 years)

TriPolar
09-29-2011, 10:43 PM
Well, I disagree with you. :)

Seriously, a spark is a spark. I get that there are components of a spark, that these components may be different temperatures and that temperature may even be irrelevant for some components or some sparks.

But we're not the Nobel committee and we're not drafting legislation. Surely, we can read between the lines to find a way to reasonably answer "What's the temp of a static charge spark?"

(Especially after 8 years)

You know what? You're right. It's time to settle this.

The answer is 5.

JBDivmstr
09-30-2011, 12:58 PM
You know what? You're right. It's time to settle this.

The answer is 5.

Would that be a 'metric' 5? Because I came up with 6-7/8. :p

TriPolar
09-30-2011, 01:09 PM
Would that be a 'metric' 5? Because I came up with 6-7/8. :p

Avoirdupois

Cheshire Human
10-02-2011, 07:51 PM
I entirely forgot about this thread (if that's not obvious). I still work in the same place though and the ESD lab is still next door.

*Skinny writes himself a note*

Mr. Skinny seems to have lost the note. He's not very good at getting back to threads, is he?

:rolleyes:;):):D

johnpost
10-02-2011, 11:11 PM
I entirely forgot about this thread (if that's not obvious). I still work in the same place though and the ESD lab is still next door.

*Skinny writes himself a note*

Mr. Skinny seems to have lost the note. He's not very good at getting back to threads, is he?

:rolleyes:;):):D

maybe he didn't loose the note. a spark might have set the note on fire.

Cheshire Human
10-10-2011, 01:32 PM
maybe he didn't loose the note. a spark might have set the note on fire.

Well, I said "lost", the past tense of "to lose". You said "loose", an archaic form of some form of past tense for "to let loose", "to release", "to let go of", or something like that, which I can't remember the proper grammatical term for. Your misspelling suggests a likelier scenario. It was windy when he was walking outside. He let loose of it, and it blew away. Let's keep bumping this every year or so until he remembers. Maybe he'll come back again in a few years, with the answer. :D

Mr. Skinny
10-11-2011, 02:47 PM
OK. Finally got a (non) answer. The folks I work with say they've never measured the temperature, but it would depend on many variables - the humidity in the air, the length of the spark gap, and the voltage across the gap.

They were able to say that the reason one doesn't get burned is because the contact with the skin is only for a nano-second - so not enough time to do any damage to the skin.

I was hoping to get a more factual answer, but there you have it.

TxTtech
06-04-2012, 03:16 PM
I have searched around the web and find numerous temperature ranges for sparks, arcs, plasma...

Are all of these just estimates or have they actually been measured? If they are measured, how was this accomplished? I am trying to find a way to measure the temperature of a spark but all I find are range values with no indication of method.

Any ideas?

am77494
06-04-2012, 04:55 PM
OK. Finally got a (non) answer. The folks I work with say they've never measured the temperature, but it would depend on many variables - the humidity in the air, the length of the spark gap, and the voltage across the gap.

They were able to say that the reason one doesn't get burned is because the contact with the skin is only for a nano-second - so not enough time to do any damage to the skin.

I was hoping to get a more factual answer, but there you have it.


Temperature is a macroscopic property - that is you need some matter to average it out. Parts of the spark will be 1000s of degrees and parts will be not - just like a rainbow. You can use a spectrograph to take a picture and an analysis of the spectrum will give you a broad range of temperatures (same as a flame).

As to why it would not burn you ----- it just does not have enough energy. Its like dropping a rice seed on someone from the top of the Eifel tower versus dropping a potted plant. Although, they will be travelling at pretty much the same speed (okay neglect air-resistance / terminal velocity for this example) - the rice wont hurt you.

ZenBeam
06-04-2012, 05:16 PM
You can use a spectrograph to take a picture and an analysis of the spectrum will give you a broad range of temperatures (same as a flame).This sounds like the best approach. Examine the spectrum for how closely it conforms to a black body spectrum. If it fits well, there's your temperature. If it kind-of fits, the temperature is less well-defined. If it doesn't fit at all, then it's reasonable to say that a spark doesn't really have a well-defined temperature.

alysdexia
12-31-2015, 04:29 PM
The instantaneus temperature of a tribčlectric spark is room temperature. It also lasts for microseconds to milliseconds, not nanoseconds.

The spark has positive and negative charges that drift in opposite lodes; this motion is work that is simply imposed on the temperature of the medium. As the spark lasts for finite and longer time, this work is gradually transferred and equiparted to the medium itself which warms up. As the medium itself does not incandescently break down into plasma, it stays only as hot as several thousand kelvins. Temperature includes a distribution of motion, so when I say the medium isn't a plasma, I mean the average motion; of course it includes some molecules that are at a plasma. If you confine the spark in a furnace or tube you can get člectric arc or collider temperatures.

Bill Beaty is mostly a'talking out his arse. There's no such thing as a "perfect vacuum"; a vacvum includes the far-field of matter everywhere so it has nonunary refractive index and nonnihilary mass; the Lamb shift imposes a 1GHz component everywhere and Zitterbewegung imposes a 10ZHz component everywhere. If you put a vacvum-breakdown voltage it's your člectrodes that break down and make the medium. There's no such thing as a perfect insulator either; watter has a conductivity thanks to aýtoionism.

RetroVertigo
12-31-2015, 04:52 PM
The rare triple-zombie thread seen here in its own habitat. Shhhhhhh.

rat avatar
12-31-2015, 05:54 PM
OK I lost a detailed response to this zombie thread due to authentication timeouts but you can calculate the temperature through Planks law as the arc column is related to black body radiation. The visible part of the electrical arc is not produced by the arc column but due to the high energy photons from the arc column interacting with surrounding matter. The ionization of oxygen and the production of ozone etc... is responsible for what we see. The arc column temperatures are much higher in a earth atmospheric static discharge and it actually produces photons of such high energy that they are ultraviolet.

If you google "ultraviolet catastrophe" you will see how classical physics breaks down at these short wavelengths with the Rayleigh–Jeans law. The math behind Planks law is way too complex for me to re-do another reply but as there is a significant amount of ultraviolet light being produced we know that the arc column temperature is at least several times hotter than the surface of the sun.

rat avatar
12-31-2015, 06:08 PM
Temperature is a macroscopic property

In an effort to fight ignorance on this zombie thread this statement is only true in classical physics, which of course we now know is not "true".

Temperature is the average kinetic energy of the particles in a system and is not necessarily a macroscopic property as taught in classic thermodynamics. It is even subject to the rules of General Relativity in odd ways that can result in thermodynamic equilibrium being reached with significant differences in "local" energy due to curvature of space time via gravity etc... This equilibrium can even be reached if most of the system is a theoretical vacuum because of black body radiation of photons will exchange energy and tend towards equilibrium.

Trinopus
12-31-2015, 11:37 PM
Anecdotal evidence of no scientific value whatever... I once touched a doorknob and got a huge, long-lasting spark...which actually left a tiny pin-point burn-mark on my skin. (Tiny little freckle of black.)

Why wouldn't Wien's Law work? We see the light, and thus know the temperature?

Or Ohm's Law? We know the voltage and amperage, and thus know the energy, and energy and temperature are...um...related.

Couldn't you rig up a spark machine and send many, many sparks into a little capsule of water, and measure how much the water warms up?

This is science, me lads! Someone do the actual experiment!

rat avatar
01-01-2016, 12:24 AM
Anecdotal evidence of no scientific value whatever... I once touched a doorknob and got a huge, long-lasting spark...which actually left a tiny pin-point burn-mark on my skin. (Tiny little freckle of black.)

Why wouldn't Wien's Law work? We see the light, and thus know the temperature?

Or Ohm's Law? We know the voltage and amperage, and thus know the energy, and energy and temperature are...um...related.

Couldn't you rig up a spark machine and send many, many sparks into a little capsule of water, and measure how much the water warms up?

This is science, me lads! Someone do the actual experiment!

The problem with Wien's Law is that it measures radiant power, the only visible light caused by the surrounding particles that is a result of them absorbing the energy from the arc column. If you wanted to measure the average temperature of the visible arc it would be usable but we are looking for peak temperature and not the the average of the visible arc correct?

I may be wrong but even with starts Wien's law only tells you the surface temperature. If you use it against the sun which works out to ~6000K where the arc column of lightning is closer to 30,000 K which makes even Regulus look cold at 10,300K. As very little of emission from the arc column is in the visible range I also believe that Wienn's law brakes down.

I guess you could derive the amount of energy required to cause the ionization and visible light emission based on the known components of the atmosphere but I personally decided it would be easier to calculate the energy released by the arc and calculate the energy transfer and temperature as it would only include the arc column and thus should approximate the peak temperature.

Trinopus
01-01-2016, 03:34 PM
. . . I may be wrong but even with starts Wien's law only tells you the surface temperature. . . .

If it worked (and I'm not at all certain either!) it would at least be a "first approximation" to an answer to the OP.

(I realized, much too late, that the experiment of using sparks to heat water would only tell you what you already knew: the energy in the spark, not the heat. Oh, well!)

KarlGauss
01-01-2016, 04:11 PM
The rare triple-zombie thread seen here in its own habitat. Shhhhhhh.
I think there's an outbreak (http://boards.academicpursuits.us/sdmb/showthread.php?t=226844)!

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