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About Electrons And Photons


hazelm

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I quote from "A Brief History of Time" by Stephen  Hawking:  "When an electron changes from one allowed orbit to another one nearer to nucleus, energy is released and a real photon is emitted  ---  which can be observed by visible light by the human eye, if it has the right wave length....."

 

Is what is visible to the human eye the sparks we sometimes see when plugging a cord into an outlet (or when removing the same)?  Or when an electrician touches a wire with something of a certain metal? 

 

Thank you.

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I quote from "A Brief History of Time" by Stephen  Hawking:  "When an electron changes from one allowed orbit to another one nearer to nucleus, energy is released and a real photon is emitted  ---  which can be observed by visible light by the human eye, if it has the right wave length....."

 

Is what is visible to the human eye the sparks we sometimes see when plugging a cord into an outlet (or when removing the same)?  Or when an electrician touches a wire with something of a certain metal? 

 

Thank you.

Yes, more or less. An electric spark excites electrons all the way up to kicking them out completely, making ions. When they drop back down they emit light, some of it visible. You will have ions and excited states of nitrogen, oxygen and also a bit of the metals of which the electrical contacts are made (the heat will vaporise a bit of them).

 

I cannot find quickly a definitive explanation of the blue colour we often see, though one (slightly unconvincing) reference states that this is due to excited states of oxygen and nitrogen. Perhaps that is right, though I'd prefer to see an article identifying which lines in the emission spectrum of N and O are responsible and why.

 

In fact, sparks between carbon electrodes are commonly used in spectrometers. We used to use one in the labs of the luboil plants where I worked, with a carbon electrode that dipped into the oil sample and then struck a spark (or better, an arc) across to another electrode. We could work out from the intensity of certain spectral lines the concentrations of elements such as calcium, magnesium and zinc in the oil.   

Edited by exchemist
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Yes, more or less. An electric spark excites electrons all the way up to kicking them out completely, making ions. When they drop back down they emit light, some of it visible. You will have ions and excited states of nitrogen, oxygen and also a bit of the metals of which the electrical contacts are made (the heat will vaporise a bit of them).

 

I cannot find quickly a definitive explanation of the blue colour we often see, though one (slightly unconvincing) reference states that this is due to excited states of oxygen and nitrogen. Perhaps that is right, though I'd prefer to see an article identifying which lines in the emission spectrum of N and O are responsible and why.

 

In fact, sparks between carbon electrodes are commonly used in spectrometers. We used to use one in the labs of the luboil plants where I worked, with a carbon electrode that dipped into the oil sample and then struck a spark (or better, an arc) across to another electrode. We could work out from the intensity of certain spectral lines the concentrations of elements such as calcium, magnesium and zinc in the oil.   

"Atomic Emission Spectrum".   Is that the spectrum we are talking about?  It is not what I always think of as a spectrum.  So, I am also confused.  This is an old book of the elements.  Excellent information in it.  Then a special double-spread page for each element.  With a magnifier I do see the lines:  blue and red.  The red are interesting in their shades.

 

Anyway, I'll go to his explanations and see if anything sounds like what you want.

 

As for the excited sparks, I think I see why we are told to plug into the outlets before we plug in smaller items. Or, before we turn on the device if it is what we plug into the wall.  Ex:  To charge the cell phone, first plug the charger into the wall outlet and then plug it to the cell phone.  Then unplug in reverse order.  Don't turn on the radio before plugging it in.  A lot of other such rules like what to do when changing a light bulb.  Always avoiding sending a powerful surge into a small devuce.  Interesting.

 

I shall return if I find anything about the blue.  Even if I have it wrong.  :-)

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All I find is the answer to "Why is the sky blue?"  Answer is because our atmosphere is mainly oxygen and nitrogen.   Theodore Gray says: "At -183°C oxygen is a pale blue liquid."  

No the sky is not blue because of emission from excited oxygen or nitrogen, but due to something called Rayleigh scattering.

 

Very tiny dust particles in the air scatter light and they scatter the short wavelengths more than the long ones. So while the other colours come through from the sun more or less directly, the blue is preferentially deflected and bounces around in the sky before it gets down to ground level, making the blue light come from all over the sky, while the rest comes direct from the sun.

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No the sky is not blue because of emission from excited oxygen or nitrogen, but due to something called Rayleigh scattering.

 

Very tiny dust particles in the air scatter light and they scatter the short wavelengths more than the long ones. So while the other colours come through from the sun more or less directly, the blue is preferentially deflected and bounces around in the sky before it gets down to ground level, making the blue light come from all over the sky, while the rest comes direct from the sun.

Coincidence.  That is what I just came back  with.  Have you seen this and is there anything here?  https://en.wikipedia.org/wiki/Rayleigh_scattering   .  I think, from your later posts, that I do not understand your question.  I'd best leave it to you.

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