- #1
PenderJ
- 14
- 4
Do suspended sub-micron sized particles influence the index of refraction of a liquid?
Suspended particles and the index of refraction
- Thread starter PenderJ
- Start date
In summary, the presence of suspended sub-micron sized particles can affect the index of refraction of a liquid, particularly for visible light which falls into the realm of Mie Scattering. Removing these particles can result in a lower reading on a refractometer due to the elimination of scattering. For particles smaller than lambda/pi, they are inductive and their radiation lags behind the incident E and B waves, resulting in a slower radiation and an increased index of refraction for the material.
- #2
PenderJ
- 14
- 4
I guess it isn't an intermediate question. How do you edit it to change the level? Is there a level that corresponds to it being too hard for this forum? 
- #3
hutchphd
Science Advisor
Homework Helper
- 6,557
- 5,660
For visible light this is a scattering problem of some complexity: ##1\mu m=10^4Angstrom##so the particles are slightly larger than the wavelength so this is the realm of Mie Scattering and not just the index of refraction which is usually applied to more homogeneous materials. Certainly the physics is interesting .
- #4
PenderJ
- 14
- 4
So when I filter out these particles and observe a lower reading in a refractometer I'm actually observing a change due to the elimination of scattering. And predicting this quantitatively would be complicated. Is that correct?
- #5
tech99
Science Advisor
Gold Member
- 2,790
- 1,291
When you say sub micron, are we talking about smaller than the light wavelength?
- #6
hutchphd
Science Advisor
Homework Helper
- 6,557
- 5,660
What type of refractometer? The answer to your question is very probably yes. Is the liquid with particles still nearly transparent?
- #7
PenderJ
- 14
- 4
I'm using 0.45 micron filters. The liquid is translucent and a little cloudy prior to filtration and has good clarity afterwards. The liquid is espresso coffee.
I have an el cheapo ($25) hand held optical refractometer, the kind where you look for the shadow line through the eyepiece. Prior to filtration the line is fuzzy but it is also higher on the scale. I have read about the same phenomenon (higher reading, less precise) being observed with more expensive electronic refractometers.
I was just curious what exactly was going on to change the reading. I get the fuzzy part, being that the liquid is cloudy. But why would it read higher?
I have an el cheapo ($25) hand held optical refractometer, the kind where you look for the shadow line through the eyepiece. Prior to filtration the line is fuzzy but it is also higher on the scale. I have read about the same phenomenon (higher reading, less precise) being observed with more expensive electronic refractometers.
I was just curious what exactly was going on to change the reading. I get the fuzzy part, being that the liquid is cloudy. But why would it read higher?
- #8
tech99
Science Advisor
Gold Member
- 2,790
- 1,291
This is what I suggest is happening. If the particles are smaller in diameter than lambda/pi then they are too small for resonance. This means they are inductive. The incident E-field causes a circumferential current on the surface of the particle and this current lags the E-field by 90 degrees. The current results in radiation which is 90 degrees delayed relative to the incident E and B waves. So the radiation from the particles is slower than free space. This gives the material an increased Index of Refraction.
- #9
PenderJ
- 14
- 4
tech99 said:
Excuse my ignorance but by lambda/pi do you mean roughly 1/3 the wavelength of light? The particles I'm talking about are larger than 450nm.
What are suspended particles?
Suspended particles are small solid or liquid particles that are dispersed in a gas or liquid medium. They can range in size from nanometers to micrometers and can be found in natural environments such as air, water, and soil, as well as in industrial processes.
How do suspended particles affect the index of refraction?
Suspended particles can affect the index of refraction of a medium by altering its optical density. This is because the particles have a different refractive index than the surrounding medium, causing light to scatter and bend as it passes through. This can result in a change in the overall index of refraction of the medium.
What is the index of refraction?
The index of refraction is a measure of how much light is bent as it passes through a medium. It is defined as the ratio of the speed of light in a vacuum to the speed of light in the medium. The index of refraction is influenced by factors such as temperature, pressure, and the presence of suspended particles.
How is the index of refraction measured?
The index of refraction can be measured using a refractometer, which measures the angle of refraction of a light beam passing through a sample of the medium. Another method is to use a spectrophotometer, which measures the amount of light absorbed or transmitted through the medium at different wavelengths.
What are some applications of understanding suspended particles and the index of refraction?
Understanding suspended particles and the index of refraction has many practical applications. It is important in fields such as environmental science, where it can help monitor air and water quality. It is also crucial in industries such as food and beverage production, where the index of refraction is used to determine the sugar content of liquids. Additionally, understanding these concepts is essential in the development of optical devices and materials, such as lenses, prisms, and fiber optics.
Similar threads
-
Classical Physics