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Jenni
Banned
Posts: 9526
Location: England.
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 Posted: Sat, 25th Nov 2006 13:41 Post subject: A physics question. |
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If you have two electrodes in a vacuum and passed a current through them. Would it produce a spark?
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TheSaint
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Posts: 6586
Location: Cook Islands
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| Posted: Sat, 25th Nov 2006 13:51 Post subject: |
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Spark needs o2 to ignite right? In a vacuum there is no o2. So i dont think it will spark.
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| Posted: Sat, 25th Nov 2006 13:52 Post subject: Re: A physics question. |
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| Jenni wrote: | | If you have two electrodes in a vacuum and passed a current through them. Would it produce a spark? |
I don't think so. Electrons need a medium to move (air), they can't just fly from one electrode to another. |
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Jenni
Banned
Posts: 9526
Location: England.
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| Posted: Sat, 25th Nov 2006 13:57 Post subject: |
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But doesn't a copper electrode have oxygen in it?
I mean copper does have oxygen in there.
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| Posted: Sat, 25th Nov 2006 14:04 Post subject: |
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| Jenni wrote: | But doesn't a copper electrode have oxygen in it?
I mean copper does have oxygen in there. |
It doesn't, in a vacuum that is. In air, oxygen reacts with the copper forming copper oxide. |
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| Posted: Sat, 25th Nov 2006 15:59 Post subject: Re: A physics question. |
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| compubrain3000 wrote: | | Jenni wrote: | | If you have two electrodes in a vacuum and passed a current through them. Would it produce a spark? |
I don't think so. Electrons need a medium to move (air), they can't just fly from one electrode to another. |
Actually sparking would occur more easily in vacuum than in air since air provides resistance to the flow of electrons. Only thing is that the spark (or eventual arc) would be invisible. However it would depend on the potential difference between the electrodes and distance between the electrodes. To create a spark in air voltage of the order of millions of volts is required.
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| Posted: Sat, 25th Nov 2006 16:07 Post subject: Re: A physics question. |
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| swingman wrote: | | compubrain3000 wrote: | | Jenni wrote: | | If you have two electrodes in a vacuum and passed a current through them. Would it produce a spark? |
I don't think so. Electrons need a medium to move (air), they can't just fly from one electrode to another. |
Actually sparking would occur more easily in vacuum than in air since air provides resistance to the flow of electrons. Only thing is that the spark (or eventual arc) would be invisible. However it would depend on the potential difference between the electrodes and distance between the electrodes. To create a spark in air voltage of the order of millions of volts is required. |
You're wrong, trust me. You can't have a spark in a vacuum, nor can you conduct electricity in a vacuum  |
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| Posted: Sat, 25th Nov 2006 16:19 Post subject: |
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http://en.wikipedia.org/wiki/Vacuum_arc
As I said it would not be your typical spark or arc since it would not be visible. Vacuum tubes have been using this principle since the dawn of the electronics age.
Knowing you however, you will now probably come up with the argument that perfect vacuum is unachievable or something similar. Don't believe me if you want, but electrons can travel even through space. The only thing is that they interact with matter and lose their charge.
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| Posted: Sat, 25th Nov 2006 16:28 Post subject: |
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| swingman wrote: | http://en.wikipedia.org/wiki/Vacuum_arc
As I said it would not be your typical spark or arc since it would not be visible. Vacuum tubes have been using this principle since the dawn of the electronics age.
Knowing you however, you will now probably come up with the argument that perfect vacuum is unachievable or something similar. Don't believe me if you want, but electrons can travel even through space. The only thing is that they interact with matter and lose their charge. |
| Quote: | The question is actually fairly tricky because the word "spark" is not well defined. Usually by "spark" we mean a momentary flow of electricity through a medium that does not usually conduct electricity. We have sparks through air, but not through metal. When we think of the word "spark" we think of a bright flash. The word "arc" usually connotes a continuous flow of electricity. Like an arc welder.
A good vacuum is a very good insulator. Much better than air because there are no molecules to ionize and participate in an avalanche. However, researchers who work with high-vacuum, high-voltage equipment know that little "sparks" occur in vacuum with a few thousand volts or more. We do not know why it happens, but we think it has something to do with dirt or dust on charged surfaces. The strange thing is that these sparks are little points of light that do not apparently jump between anything, like a normal spark.
It is possible to have a stream of electrons travel in a vacuum. To do this the emitter must be sharply pointed and the applied voltage must be large. Electrons come off the sharply pointed emitter. This is the basis of the field-emission electron microscope. But these electrons do not make light, so they are not a "spark" or "arc" as commonly used. So, no, it does not seem possible to have a 'spark' in the conventional sense in a good vacuum.
There is something called a "triggered vacuum spark-gap switch." It at first seems like a switch based on a spark through a vacuum, but the current is really conducted by a tiny burst of evaporated metal atoms, which carry the current like air ions do. |
http://www.newton.dep.anl.gov/newton/askasci/1993/physics/PHY102.HTM |
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| Posted: Sat, 25th Nov 2006 17:32 Post subject: |
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| swingman wrote: | | So I guess there wouldn't be a 'spark' in vacuum. Thanks for clearing that up Compu. |
You're welcome |
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| Posted: Sat, 25th Nov 2006 21:00 Post subject: Re: A physics question. |
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| compubrain3000 wrote: | | Jenni wrote: | | If you have two electrodes in a vacuum and passed a current through them. Would it produce a spark? |
I don't think so. Electrons need a medium to move (air), they can't just fly from one electrode to another. |
Might be some exotic quantum effect that enables this?
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| Posted: Sat, 25th Nov 2006 21:06 Post subject: |
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If the potential difference is great enough then electrons can flow across point A to B, overcoming any resistance inbetween. There is no perfect insulator as far as I know. Isn't this the principle behind radio waves? - The top of the aerial is a fine point and electrons accumulate here with a vast pressure behind them, have 'nowhere to go' and jump into the ether as a waveform. I remember reading years back that electrons are 'weird' in that they have both properties of a wave and of matter - so their behaviour can't be easily characterised?
You wanted a Miracle, I give you the F. B. Eye !!
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| Posted: Sat, 25th Nov 2006 23:48 Post subject: |
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| TheBugulous wrote: | | If the potential difference is great enough then electrons can flow across point A to B, overcoming any resistance inbetween. There is no perfect insulator as far as I know. Isn't this the principle behind radio waves? - The top of the aerial is a fine point and electrons accumulate here with a vast pressure behind them, have 'nowhere to go' and jump into the ether as a waveform. I remember reading years back that electrons are 'weird' in that they have both properties of a wave and of matter - so their behaviour can't be easily characterised? |
Electrons exhibit properties of both waves and of particles. If provided with high enough energy, they can become free in a vacuum due to their wave-like properties. |
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