How can frequency be used to calculate refractive index?

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    Index Refractive index
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Discussion Overview

The discussion revolves around the calculation of the refractive index of a medium using only the frequency of light entering from air. Participants explore the relationship between frequency, wavelength, and the refractive index, considering the implications of dispersion and absorption.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant inquires about calculating the refractive index using only the frequency of light, suggesting the formula n = (speed of light in vacuum) / (speed of light in medium).
  • Another participant asserts that it is not possible to calculate the refractive index without a formula that relates it to frequency or wavelength.
  • A third participant acknowledges the lack of information in the problem, indicating uncertainty about the calculation.
  • One participant presents the idea that for real indexes of refraction, Re(n(λ)) = c/v(λ), and notes that if the index varies with wavelength, it implies both absorption and dispersion, leading to a complex index of refraction.
  • Another participant reiterates the challenge of not having the velocity v(λ) or wavelength in the medium, despite being able to derive λ in air from the frequency.
  • A further comment emphasizes that for any n(λ), the velocity v(λ) can be expressed as v(λ) = c/Re(n(λ)), but this still does not resolve the lack of information about v(λ) in the current context.

Areas of Agreement / Disagreement

Participants generally agree that the problem lacks sufficient information to calculate the refractive index using only frequency. Multiple views are presented regarding the relationship between frequency, wavelength, and refractive index, indicating ongoing uncertainty and exploration of the topic.

Contextual Notes

The discussion highlights limitations related to missing information about the speed of light in the medium and the relationship between frequency and wavelength in this specific scenario.

Francy
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How can i calculate the refractive index knowing only the frequency of the light entering the medium from air?

n(refractive index) = (speed of light in vacuum) / (speed of light in medium)
 
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You can't, unless you are provided with a formula for the refractive index in terms of frequency or wavelength.

p.s. Welcome to Physics Forums.
 
Last edited:
Yeah, I think the problem I have here doesn't have all the information. Thanks anyway! Thanks also for welcoming me here ^^
 
I believe that for real indexes of refraction, Re (n(λ)) = c/v(λ).

If the index of refraction varies with wavelength (dispersion), then there is absorption as well as dispersion, which is equivalent to a complex index of refraction. See http://en.wikipedia.org/wiki/Refractive_index
See in particular the section on Complex index of refraction and absorption.
 
Bob S said:
I believe that for real indexes of refraction, Re (n(λ)) = c/v(λ).
But in this situation we don't have v(λ), we only have the frequency [itex]\nu[/itex]. From that we can get λ in air, but not λ in the medium or v(λ) for that matter.
 
Redbelly98 said:
But in this situation we don't have v(λ), we only have the frequency [itex]\nu[/itex]. From that we can get λ in air, but not λ in the medium or v(λ) for that matter.
I should have said for ANY n(λ), the velocity v(λ) = c/Re (n(λ))
 

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