How does a prism affect wavelength?

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    Prism Wavelength
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Discussion Overview

The discussion revolves around the effects of a prism on the wavelength and speed of light, particularly focusing on the relationship between these properties during the dispersion of light. Participants explore theoretical aspects, implications of different media, and the nature of light's behavior in prisms.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants note that prisms create dispersion, causing different frequencies of light to travel at different angles, and question how this affects wavelength and speed.
  • One participant explains that while the speed of light changes in a prism, the frequency remains constant, leading to a change in wavelength that is inversely proportional to the index of refraction.
  • Another participant asserts that the speed of light is constant in every medium, but this claim is contested, with clarification that it is constant in a vacuum.
  • There is a discussion about the nature of light in different media, with one participant suggesting that the interaction of light with a medium involves a delay due to absorption and emission processes.
  • A later post reiterates that the light emerging from the prism retains its original frequency and wavelength, suggesting that the prism only alters the angle of the light.

Areas of Agreement / Disagreement

Participants express differing views on whether the wavelength changes as light passes through a prism, with some asserting it does and others claiming it does not. The discussion remains unresolved regarding the exact nature of the relationship between wavelength, speed, and the effects of the prism.

Contextual Notes

There are unresolved assumptions regarding the definitions of speed in different media and the implications of dispersion on wavelength. The discussion also touches on the complexities of light behavior in various contexts, which may not be fully addressed.

caseytrimble
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I know that prisms create dispersion and cause different frequencies of light to travel at different angles relative to the normal, and that the prism affects the wavelength and speed of the waves, but what exactly is the nature of this relationship? Other than spreading various frequencies out, does the wavelength measurably change? If so, how? Does it contract, does it expand?
 
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The speed of light changes but the frequency of the light stays the same. So this means that the wavelength must change accordingly since the product of the frequency and wavelength is the speed of light (in this case at least, there is technically a difference between phase and group velocities but no need to get into that here). Since the relationship is directly proportional between the speed of light and wavelength, then the wavelength must decrease since the prism has a higher index of refraction than the air. Of course, if you immersed your prism in some kind of liquid or dielectric that had a higher index of refraction than the prism itself then you should find that the wavelength increases since the speed of light in the prism would be faster than the external background medium.
 
Well according to the General Relativity, the electromagnetic disturbance travels at a constant speed called the speed of light. This speed is the same in every medium.
 
Last edited:
ProTerran said:
This speed is the same in every medium.

No, it is not. When we say "constant speed of light" we mean in a vacuum.

The speed of light in water was first measured by Fizeau around 1850.
 
Ii's true that the speed of light is the maximum speed which electromagnetic disturbance travels in vacuum. But the point is that water is also consisting almost of a vacuum. So in fact what you measure is a delay between absorption and emission of the light passing by given medium (it is stochastic process).

Hope my English is good enough and you get the idea :-)
 
caseytrimble said:
I know that prisms create dispersion and cause different frequencies of light to travel at different angles relative to the normal, and that the prism affects the wavelength and speed of the waves, but what exactly is the nature of this relationship? Other than spreading various frequencies out, does the wavelength measurably change? If so, how? Does it contract, does it expand?
Just to clarify:

What happens in the prism stays in the prism.

When the light emerges, it has the same frequency and wavelength as when it entered. The prism permanently alters nothing but angle.
 

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