How does the wavelength change the amount of refraction?

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Discussion Overview

The discussion centers on the relationship between wavelength and the amount of refraction experienced by light, particularly in the context of using different colored lasers (green vs. red) and the behavior of light as it passes through various materials, such as prisms. The scope includes theoretical explanations and observations related to optical phenomena.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants note that a material's index of refraction is dependent on wavelength, typically increasing as the wavelength decreases, leading to greater refraction of green light compared to red light.
  • One participant questions the expectation that refraction would be the same for all frequencies, highlighting the frequency dependence of wave phenomena.
  • Another participant points out that while the behavior of prisms illustrates this concept clearly, it is not a universal rule, as nondispersive media do not exhibit frequency-dependent refraction.
  • There is a discussion about the conditions under which dispersion occurs, with one participant mentioning that even in nondispersive media, different frequencies can still travel at different speeds.
  • Concerns are raised about the visibility of dispersion effects depending on the shape of the medium, with examples such as prisms and raindrops illustrating significant separation of wavelengths.

Areas of Agreement / Disagreement

Participants express differing views on the generality of the relationship between wavelength and refraction, with some agreeing on the wavelength dependence in dispersive media while others highlight exceptions in nondispersive contexts. The discussion remains unresolved regarding the nature and prevalence of nondispersive media.

Contextual Notes

Limitations include the dependence on specific definitions of dispersive and nondispersive media, as well as the range of frequencies considered in different contexts.

Muggo
Using a green laser instead of a red laser seems to change the way the ray changes during refraction. Why is that so?
 
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A material's index of refraction is wavelength/frequency dependent and typically increases as the wavelength decreases. Hence why green light is refracted more than red light when passing through something like a prism.
 
Muggo said:
Using a green laser instead of a red laser seems to change the way the ray changes during refraction. Why is that so?
Just as an aside, have no you not ever seem a prism in action? It splits a white light beam into a spectrum of colors using exactly the mechanism described by Drakkith, so it's hardly surprising that you are getting the results you are getting.
 
I could throw the question back to the OP and ask why he would expect the refraction to be the same for all frequencies. The spectrum of visible light covers about an octave of frequencies so it's hardly surprising that a phenomenon which involves 'lag' of waves would be frequency dependent.
 
I feel I should point out that with a prism, this is obvious but it's not a general rule. If the propagation medium is nondispersive, for example, then there's no frequency dependence for the phase velocity and therefore refraction.
 
boneh3ad said:
If the propagation medium is nondispersive,
That would depend upon the range of frequencies involved. Nothing works the same from DC to daylight.
 
boneh3ad said:
I feel I should point out that with a prism, this is obvious but it's not a general rule. If the propagation medium is nondispersive, for example, then there's no frequency dependence for the phase velocity and therefore refraction.

The only reason it's obvious with a prism is because of its shape, in other words the shape is such that the separation of the wavelengths can be quite large. The same goes for other shapes such as spheres, eg raindrops forming rainbows, and lenses which suffer from chromatic aberation.
With other shapes, for example a parallel sided glass block, the separation due to dispersion can be so small that it may not be noticeable. But even with normal incidence where the there is no separation there is still dispersion because the different frequencies travel at different speeds.
But and this is the main reason I replied to this, are there any nondispersive media apart from a vacuum?
 

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