Does the frequency of light changes when it go through a prism

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Discussion Overview

The discussion revolves around the behavior of light as it passes through a prism, specifically focusing on whether the frequency of light changes and the implications of such changes on energy and color perception. The scope includes conceptual understanding and technical reasoning related to optics.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Technical explanation

Main Points Raised

  • Some participants assert that the frequency of light does not change when it passes through a prism, and therefore the energy remains constant, while the wavelength and speed change in the medium.
  • Others question this view, suggesting that if the frequency changes, it could imply that light separates into different rays with varying frequencies and energies.
  • One participant proposes that red light entering a prism does not change color inside the prism, maintaining its frequency and energy, which determines the perceived color.
  • Another participant mentions that the intensity and energy density of the light wave may decrease due to partial reflection at the air-glass boundary.
  • There is a reference to Newton's experiment with prisms, where he demonstrated that the prism separates white light into its constituent colors.
  • A later reply introduces a discussion about associated momentum and mass in relation to the frequency of light, indicating a more complex consideration of light's properties.

Areas of Agreement / Disagreement

Participants express differing views on whether the frequency of light changes when passing through a prism. Some maintain that it does not change, while others propose that it could. The discussion remains unresolved with multiple competing perspectives.

Contextual Notes

There are unresolved assumptions regarding the definitions of frequency, energy, and color perception in the context of light passing through a prism. The discussion also touches on the implications of partial reflection and the behavior of light in different media.

Rico L
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I know the prism can separate the light into 7 colours, but my teacher said the frequency of light changes and so as the wavelength..



if he is right... this is the bit i am not sure about

if the frequency of the light changes when it passes through a prism, does it mean the energy also changes? if it does, does it mean that when the light goes through a prism, it changes into 7 different rays which that we don't regard them as the visible light because they all have different frequency and energy ?

please correct me

i am not even sure about my basic knowledge

many thanks
 
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The frequency does not change when light enters a prism, but the intensity and energy density of the light wave decreases somewhat due to partial reflection of the wave at the air-glass boundary.
 
fluidistic said:
Ok so basically a red light (wavelength of around 600 nm) entering say a prism whose refractive index is 1.5 becomes violet (wavelength of about 400 nm) in the prism, am I right?

No, the light is still red inside the prism. The frequency of the light (or energy of the associated photons, E = hf) is what fundamentally determines the color that we perceive. We usually relate color to wavelength (in vacuum or practically, in air) because wavelength is easier to measure directly.
 
jtbell said:
No, the light is still red inside the prism. The frequency of the light (or energy of the associated photons, E = hf) is what fundamentally determines the color that we perceive. We usually relate color to wavelength (in vacuum or practically, in air) because wavelength is easier to measure directly.

Ok thank you, amazing. :smile:
 
All the frequencies ( or colors) make up white light. The prism separates them. When Newton did this he also used a second prism placed so the spectrum coming out of the first prism was mixed back into white light which exited the second prism.
 
jtbell said:
...the associated photons, E = hf

Wait a minute. Using this same logic I get an associated momentum, p=h_bar k; an increase in momentum and an imaginary mass.
 

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