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which occurs first lightning or thunder?

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EdEarl    648

Nearly instantaneous is still slower than simultaneous.

True, but having been close to a lightning strike, I can say there is no perceivable difference between flash and sound, and that up close thunder sounds like a loud spark, "crack."

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Bender    132

Moreover, it is the heating which happens nearly instantaneous. The movement of air can only happen after the heating.

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DrP    347

QUOTE EE: ..."no perceivable difference.."

 

Of course not, how would your human senses detect that? The spark, however, DOES come before the bang.... there is no 'perhaps' about it, we know this.

 

 

PS: The use of "perhaps" and confusing the simple issue by talking about irrelevant ions in a vacuum was why I gave you a -1 earlier, although studiot thought your post worth a +1. My - 1 may have been a bit harsh and I do now regret it, but I have given you loads of +'s in the past (I think) so only thought it right to give you a neg too when you throw doubt on what we know to be true but saying "perhaps". I hate saying when I have given positive or negative rep - there is as reason it is confidential, and I hate this recent sycophantic trend of creepily posting "I gave you +1 for that"... it is so slimy and bloody irritating.

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EdEarl    648

Perhaps you can clear up something I do not understand. Electrons don't move at the speed of light, but IDK how fast ions are created nor how fast an atom heats as it becomes ionized. A spark flows through ions; thus, I assume a spark is the movement of electrons as quickly as atoms become ionized. How much delay is there between ionization and the air becoming superheated to create the crack of a spark?

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DrP    347

I do not know what the delay is Ed, but there has to be some delay because one causes the other. You could ask when exactly does the spark begin?... Is it a spark when it is first visible or is it a spark when the first photon of light is emitted? The time measurement from these points will be different (micro seconds?). I do not even know if the exact point the discharge actually becomes defined as a spark. For the spark to cause thunder though it would need to be huge (although small sparks do make a little crack sound). None the less, this energy released to the spark heats the air and causes it to expand causing the thunder... which happens (micro seconds?) AFTER the discharge. How could it be different?


My assumption would be that you can see the light before the air has started to expand - thus the sound comes after the light. (when I say 'see' here I mean the exact point the light leaves the spark, not when it enters your eye.)

Edited by DrP

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EdEarl    648

Electrons jumping orbitals are instantaneous. When an electron makes an ion, is that movement instantaneous? Since that process pumps energy into an atom, there would be no light created. What causes the light? The blue color of ionized air seems to suggest that some electrons are moved to higher orbitals and fall back later; thus, generating light. If that is the source of light, then the electric current that ionizes and heats is invisible, and some time later light is created. However, IDK everything happening; thus, my assumptions may be wrong.

 

The superheated air/ions would create a pressure wave that spreads at the speed of sound, are you sure the pressure occurs after the light is created by electrons falling to a lower orbital, or is there more going on that I'm unaware of?

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DrP    347

I'll have to look that up when I am not at work, although I suspect you are over thinking it. When the terms lightening and thunder where introduced I do not know if they were defined tightly enough to determine the exact point in the discharge you deem the spark to be called lightening. The ionisation and energy releases you are talking about HAVE to happen before the sound though, surely, as it is this energy released by that that causes the superheating and the expansion and thus the sound. Anyway - unless I unearth something amazing and new when I look that up later I guess I can add no more. I will let a pure physicist answer you question. Regards.

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Bender    132

The air in lightning gets considerably hotter than the sun. I assume that to be the primary source of the light. In other words: as soon as the air is heated, you have lightning.

 

Then again, it depends on defining when lightning and thunder start. Heating the air initiates both the emission of photons and the emission of a pressure wave, aka thunder. So while the time constant of the light being emitted is much smaller than for the sound wave, they are both initiated by the same event.

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Ophiolite    1811

I hate saying when I have given positive or negative rep - there is as reason it is confidential, and I hate this recent sycophantic trend of creepily posting "I gave you +1 for that"... it is so slimy and bloody irritating.

Going briefly off-topic, I believe that once or twice I have advised a poster that I've given them a +1. That, and an accompanying explanation, have been to emphasise (and perhaps expand on) how relevant, accurate, useful, agreeable, etc. their post was. (I'll leave you to wonder if the +1 on your post #32 was from me. :))

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StringJunky    1486

The air in lightning gets considerably hotter than the sun. I assume that to be the primary source of the light. In other words: as soon as the air is heated, you have lightning.

 

Then again, it depends on defining when lightning and thunder start. Heating the air initiates both the emission of photons and the emission of a pressure wave, aka thunder. So while the time constant of the light being emitted is much smaller than for the sound wave, they are both initiated by the same event.

The ionic discharge which brings forth light - which is heat - superheats the air molecules which then create a shockwave. It's got to get to that temperature first, which takes time, no matter how short. That is the order of events.

Edited by StringJunky
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Bender    132

Is the air heated by light? I would have thought it was heated by resistive heating, in which case the heating happens first and then causes both light and sound.

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StringJunky    1486

Is the air heated by light? I would have thought it was heated by resistive heating, in which case the heating happens first and then causes both light and sound.

The heat is photons being emitted as the electrons in the ionised molecules go back to the rest state.

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Bender    132

But what part of the lightning we see is the photons being emitted in that way, and what part is photons being emitted because the air is hot?

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StringJunky    1486

But what part of the lightning we see is the photons being emitted in that way, and what part is photons being emitted because the air is hot?

I've no idea about the wavelengths of the photons involved/emitted in each part. Pass :)

Edited by StringJunky

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EdEarl    648

They are?

Apparently my info was wrong.

 

 

stackexchange

When the atom absorbs a photon, the electron jumps from let's say for example from the 2s to a 3p orbital, the electron is not in any orbital during that time. Its wave function can be written as a time-varying mix of the normal orbitals. A long time before the absorption, which for an atom is a few femtoseconds or so, this mix is 100% of the 2s state, and a few femtoseconds or so after the absorption, it's 100% the 3p state. Between, during the absorption process, it's a mix of many orbitals with wildly changing coefficients. There was a paper in Physical Review A back around 1980 or 1981, iirc, that shows some plots and pictures and went into this in some detail. Maybe it was Reviews of Modern Physics. Anyway, keep in mind that this mixture is just a mathematical description. What we really have is a wavefunction changing from a steady 2s, to a wildly boinging-about wobblemess, settling to a steady 3p.

This makes more sense, ty.

Edited by EdEarl
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EdEarl    648

ty. I try, but am not an expert; thus, must fess up to errors.

Edited by EdEarl

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swansont    6167

ty. I try, but am not an expert; thus, must fess up to errors.

 

 

In addition you checked it out, posted good information (including a pointer to the research) and updated your understanding. Which is in sharp contrast (unfortunately) to some discussions we have around here.

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