How can frequency be used to calculate refractive index?

  • Context: Undergrad 
  • Thread starter Thread starter Francy
  • Start date Start date
  • Tags Tags
    Index Refractive index
Click For Summary

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
Messages
2
Reaction score
0
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)
 
Science news on Phys.org
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))
 

Similar threads

Graduate Feasibility of Micro‑Plasma–Induced Refractive‑Index Phase Modulation
  • · Replies 5 ·
Replies
5
Views
440
Undergrad Outer layer refractive index - total internal refection on waveguide
  • · Replies 2 ·
Replies
2
Views
2K
Graduate Reflectivity with gradient in refractive index
  • · Replies 6 ·
Replies
6
Views
3K
Undergrad Energy Redistribution in Lorentz Oscillator Model with Pure Radiation Damping
  • · Replies 2 ·
Replies
2
Views
2K
Undergrad Light speed and refractive index
  • · Replies 25 ·
Replies
25
Views
4K
Undergrad Why is Cherenkov radiation blue? And what about refractive index?
  • · Replies 3 ·
Replies
3
Views
2K
Graduate Why does the amount of Refraction depend on wavelength?
  • · Replies 1 ·
Replies
1
Views
1K
Undergrad Is the index of refraction constant for a given medium?
  • · Replies 7 ·
Replies
7
Views
5K
Undergrad How can I derive this relation from Snell's law?
  • · Replies 1 ·
Replies
1
Views
2K
Graduate Free‑Carrier Index Modulation in Thin Transparent Layers at Visible Wavelengths
  • · Replies 2 ·
Replies
2
Views
403