What is the relation between refractive index and wavelength in a prism?

In summary, the refractive index decreases with the increase in the wavelength of the light. This is due to the phenomenon of resonance, which is the origin of normal dispersion.
  • #1
Christa
2
0
This is from my Physics practical experiments.

The experiment is to find the refractive power of the prism for different colours and also to determine the dispersive power of the material of the prism.

My question is how does the refractive index of the material of the prism vary with the wavelength of the source light used?

The answer is the refractive index decreases with the increase in the wavelength of the light.
I do not want the equation of the relation but the physical significance of the relation.
 
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  • #2
If this is for "practical experiments", then DO IT and find out! Measure the angle of refraction of several different kinds of transparent materials and wavelengths. For a "practical experiment" you shouldn't be trying to find a formula before doing the experiment.
 
  • #3
You are unlikely to find such an equation anyway because it is dependant on the composition of the glass. So unless you know the composition of the glass exactly (which I very much doubt), the only way to obtain this information is to measure it directly anyway.

Claude.
 
  • #4
The answer is the refractive index decreases with the increase in the wavelength of the light.
I do not want the equation of the relation but the physical significance of the relation.
 
  • #5
Christa said:
I do not want the equation of the relation but the physical significance of the relation.

This is a pretty open ended question - I would start with the fact that different wavelengths will travel through the glass at different speeds, which results in material dispersion - different wavelengths separate in time and space when propagating through the glass.

Claude.
 
  • #6
You can find dispersion curves (refractive index as a function of wavelength) for many materials on http://refractiveindex.info/" [Broken]
 
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  • #7
Christa said:
The answer is the refractive index decreases with the increase in the wavelength of the light.
I do not want the equation of the relation but the physical significance of the relation.

The refractive index is related to the velocity of light in the medium.
The velocity of light in the medium is related to the interactions of the incoming electric
field of the radiation ,with the electric fields in the medium.
The higher the frequency of the radiation , the more radiation/medium electric field interactions, which reduces velocity and equals a higher refractive index.
 
  • #8
mpolyanskiy said:
You can find dispersion curves (refractive index as a function of wavelength) for many materials on http://refractiveindex.info/" [Broken]

Is that your website? It's great! Very useful :-)
 
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  • #9
lichen said:
Is that your website? It's great! Very useful :-)

Thanks!

You can check also an advanced version of the site: http://dispersion.info/" [Broken]
 
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  • #10
Christa said:
<snip>
My question is how does the refractive index of the material of the prism vary with the wavelength of the source light used?

The answer is the refractive index decreases with the increase in the wavelength of the light.
I do not want the equation of the relation but the physical significance of the relation.

That is true for normal dispersion: the refractive index decreases as the wavelength increases. Until an resonance peak, that is- then there is anomalous dispersion, where the refractive index *increases* with increasing wavelength. Anomolous dispersion is responsible for those "light moving faster than 'c'" experiments.

The phenomenon of resonance is the origin of normal dispersion.
 
  • #11
Christa said:
The answer is the refractive index decreases with the increase in the wavelength of the light.
I do not want the equation of the relation but the physical significance of the relation.

The following is a more complete explanation:
At the microscale an electromagnetic wave is slowed in a material because the electric field
creates a disturbance in the charges of each atom- primarily the electron proportional to the permittivity.
The oscillation of charges itself causes the radiation of an electromagnetic wave that is slightly out of phase with the original. The sum of the two waves creates a wave of the same frequency but shorter wavelength than the original leading to slowing of the waves travel. (1)
An electron in an atom or molecule is bound there by strong restoring forces. It has a definite natural frequency. For electrons in atoms it is usually in a region corresponding to violet or U.V. light.
In mechanical systems it is possible to "drive" the system most effectively if we impress on it an external force whose frequency is as close as possible to that of the natural resonant frequency.
In the case of light the blue is closer to the natural resonant frequency of the bound electrons than red light. Therefore we would expect the blue light to be more effective in causing the electrons to oscillate. (2)
ref. :
1) http://explanation-guide.info
2)Physics Halliday-Resnick p 1077
 
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  • #12
Another link to a good site I've never seen before. This thread is a gold mine for good sites.
 

What is the purpose of a refractive index experiment?

A refractive index experiment is used to determine the refractive index of a substance, which is a measure of how much light is bent when passing through the substance. This information can be used to identify and characterize different materials.

What equipment is needed for a refractive index experiment?

The main equipment needed for a refractive index experiment includes a light source, a prism or refractometer, and a sample of the substance being tested. Other useful tools may include a ruler, a pen or pencil, and a calculator.

How is a refractive index experiment performed?

In a basic refractive index experiment, a beam of light is directed through the substance being tested and into a prism or refractometer. The angle at which the light bends is measured, and this information, along with the known angle of the prism, can be used to calculate the refractive index of the substance.

What factors can affect the results of a refractive index experiment?

The main factors that can affect the results of a refractive index experiment include the wavelength of light used, the temperature of the sample, and the presence of impurities or contaminants in the sample. It is important to account for these factors and perform the experiment under controlled conditions for accurate results.

What are some real-world applications of refractive index experiments?

Refractive index experiments have many practical applications, including in the fields of optics, chemistry, and materials science. They are used to identify and analyze materials, determine the purity of substances, and even in the production of eyeglasses and other optical devices.

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