Scattering of Light in Different Media

[new6ton]

The sky is blue because the blue wavelength is rayleigh scattered.
Now let's take a glass of water you use for drinking. The ordinary reasoning is that water is not rayleigh scattered. But If water were to be scattered by all wavelength. How should the water look like? I just want to have an idea how a liquid that can be scattered looks like.

 

[jbriggs444]

Now let's take a glass of water you use for drinking. The ordinary reasoning is that water is not rayleigh scattered.

You are trying to speak about the [lack of] Rayleigh scattering of light by water? The explanation for the lack of color in a glass of drinking water is the same as the lack of color in the air when your room is illuminated by an electric bulb -- the water and the air are quite transparent. Any scattering that is present is negligible on such scales.

You ask about the visual appearance of a near-transparent medium which scatters all frequencies identically. The answer would be "fog" -- a near-transparent medium which scatters all frequencies nearly identically.

 

[new6ton]

You are trying to speak about the [lack of] Rayleigh scattering of light by water? The explanation for the lack of color in a glass of drinking water is the same as the lack of color in the air when your room is illuminated by an electric bulb -- the water and the air are quite transparent. Any scattering that is present is negligible on such scales.

About this "negligible" portion, how does light collide with the H2O molecules? Which part of H2O does it exactly collide?

You ask about the visual appearance of a near-transparent medium which scatters all frequencies identically. The answer would be "fog" -- a near-transparent medium which scatters all frequencies nearly identically.

 

[jbriggs444]

About this "negligible" portion, how does light collide with the H2O molecules? Which part of H2O does it exactly collide?

What research have you done? A quick trip to Google finds a Wikipedia article with references.

 

[new6ton]

I just wanted to know how many percentage of photons that hit water is rayleigh scattered and why don't we see the scattered photons and what detector would it take to observe it.

I googled "how many percentage of photons that hit water is rayleigh scattered and detector".

No good hits. Although I did try to read again about Rayleigh scattering so got emphasized in it was not photoelectric effect but [Wiki]: "Rayleigh scattering results from the electric polarizability of the particles. The oscillating electric field of a light wave acts on the charges within a particle, causing them to move at the same frequency. The particle, therefore, becomes a small radiating dipole whose radiation we see as scattered light. The particles may be individual atoms or molecules; it can occur when light travels through transparent solids and liquids, but is most prominently seen in gases. "

But then, in this thread I read https://www.physicsforums.com/threa...is-the-scattering-rayleigh-scattering.956775/

"The Rayleigh theory is not applicable to liquids, but one can refer to the Einstein—Smoluchowski theory.

"In the Einstein—Smoluchowski theory, scattering is considered to be caused by the random motion of molecules which in a sufficiently small volume causes fluctuations of density and, therefore, of the dielectric constant."

So Rayleigh scattering doesn't exist in water? Whatever. How many percentage of Einstein—Smoluchowski scattering occur in water of glass? And what detector is used to detect these Einstein—Smoluchowski scattering in water?

 

[anorlunda]

I just wanted to know how many percentage of photons that hit water is rayleigh scattered and why don't we see the scattered photons and what detector would it take to observe it.

A glass of water is too little. Think bigger.

Ocean sailors are called "blue water sailors," for a reason.

 

[new6ton]

https://www.physicsforums.com/threa...is-the-scattering-rayleigh-scattering.956775/
The old thread is confusing because indeed Rayleigh scattering can occur in water (I'll show how below so if you agree please edit the old thread especially when no Science Advisor was present).

""One speaks of Rayleigh scattering in case of light scattering from molecules if the conditions for independent scattering on the single molecules are valid. When the molecules aggregate the situation changes: scattered waves coming from different parts of the aggregate interfere and partially extinguish each other. For aggregate sizes larger than a wavelength, Mie scattering predominates. And in case of a homogeneous, nonabsorbing bulk liquid you treat the interaction with light in terms of reflection and refraction."

In above, the author claimed that in water where molecules aggregate, it was Mie scattering and not rayleigh scattering.

But when you use laser photons on water, there is rayleigh scattering. In fact, it was so intense the device has to put filter against the rayleigh rays:

This is the classic raman spectrum of water with the strokes shift creating it. The intense Rayleigh incident light of 532nm was filtered.

Do you know why laser light can cause Rayleigh scattering in water?

If you agree Rayleigh scattering can occur in water, please edit the old lock post because it is incomplete or even incorrect information. I spent hours thinking of it. If it only mentions laser light can cause Rayleigh scattering in water then could have gotten it in less than a minute.

 

[sophiecentaur]

I googled "how many percentage of photons that hit water is rayleigh scattered and detector".

Google is not very good with such types of query. It may be better for you to try Rayleigh scattering and wavelength. Then look up the size of the scattering centre of interest. I actually looked up Rayleigh cross section and the second hit was this one.

 

[sophiecentaur]

Ocean sailors are called "blue water sailors,"

It's ok for you guys. It's hard to find blue water in the English Channel. All those damned clouds plus silt in the water.

 

[anorlunda]

It's ok for you guys. It's hard to find blue water in the English Channel. All those damned clouds plus silt in the water.

Too bad, you would love it. When leaving the Bahamas Grand Banks and entering the Gulf Stream, the abrupt change of color and the beauty of that impossible blue takes your breath away.

 

[Vanadium 50]

One needs to use some care when discussing water colors, as it is not a matter of depth alone. Here is where the Rio Negro and Rio Solemos meet at the headwaters of the Amazon.

 

[sophiecentaur]

Too bad, you would love it. When leaving the Bahamas Grand Banks and entering the Gulf Stream, the abrupt change of color and the beauty of that impossible blue takes your breath away.

Lah! lah! lah! lah! - I can't hear you.

Sounds just too good.

OMG you met a friend there too. Whoops - not your photograph.

 

[new6ton]

Google is not very good with such types of query. It may be better for you to try Rayleigh scattering and wavelength. Then look up the size of the scattering centre of interest. I actually looked up Rayleigh cross section and the second hit was this one.

The page is broken above. But I was simply asking whether it was Rayleigh scattering or mie scattering in bulk water:

Should you consider the bigger size of the bulk water?

But when you use a raman spectrometer on water where the incident photon is say 532nm. You get intense rayleigh scattering (backscatting) that the optics have to filter. So is it rayleigh scattering in bulk water? But why do many believe it is mie scattering? What's your take on this?

 

[sophiecentaur]

But I was simply asking whether it was Rayleigh scattering or mie scattering in bulk water:

You need to know what fraction of the radiation is actually scattered if you want to know "what the water would look like" (a question in your OP)

 

[new6ton]

You need to know what fraction of the radiation is actually scattered if you want to know "what the water would look like" (a question in your OP)

I don't want to know what the water would look like now. I just want to know first of all and categorically whether it is Rayleigh or Mie scattering that really happens in water. If it is Mie scattering, then the incident photons in raman spectroscopy is being 180 degree mie backed scattered and filtered by the optics.

 

[new6ton]

Come on guys. Let's conclude this. What is your thought?

In Raman spectrometry book. It mentioned that in liquid, it is really Rayleigh scattering.

About Mie scattering.
http://user.engineering.uiowa.edu/~ece195/2006/docs/Rayleigh.pdf
"Raleigh scattering occurs when the dimensions of the scatter is much smaller than the wavelength of the incident electromagnetic radiation. An example is when S-band radar waves are scattered by raindrops. Raleigh scattering exhibits a strong wavelength dependence. Mie scattering occurs when the dimensions of the scattered is much larger than the wavelength of the incident electromagnetic radiation. An example is when light is scattered by small water droplets in clouds. "

This is why you see clouds as white. Now in bulk water, why doesn't Mie scattering happen (contrary to the old post) when the particles seem to be much larger than the wavelength of the incident electromagnetic radiation? Why does rayleigh scattering predominate in bulk water?