Ray tracing diagram for white light moving through glass

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SUMMARY

The discussion focuses on ray tracing for white light as it passes through a sheet of glass, emphasizing the principles of refraction and dispersion. The equation n1(sin x) = n2(sin y) is central to understanding the behavior of light at the interface between air and glass. Participants clarify that light entering glass is refracted towards the normal, while exiting glass, it is refracted away from the normal, leading to a downward deflection. Additionally, the concept of dispersion is introduced, highlighting how different wavelengths of light (red and violet) are deflected at varying degrees.

PREREQUISITES
  • Understanding of Snell's Law and refractive indices
  • Familiarity with the concepts of refraction and dispersion in optics
  • Basic knowledge of ray tracing techniques
  • Ability to interpret ray diagrams in optical contexts
NEXT STEPS
  • Study Snell's Law in detail, focusing on practical applications in optics
  • Learn about the phenomenon of light dispersion and its implications in optical systems
  • Explore ray tracing software tools for simulating light behavior in different media
  • Investigate the formation of spectra and the role of refractive indices in color separation
USEFUL FOR

Students of physics, optics enthusiasts, and educators looking to deepen their understanding of light behavior in different media, particularly in relation to refraction and dispersion phenomena.

phosgene
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Homework Statement



White light is incident on a sheet of glass as shown below. Complete the ray tracing diagram.

physicsdiagram.jpg


Homework Equations



n1(sinx)=n2(siny), where n = the refractive index of the medium.

The Attempt at a Solution



The ray on the bottom is hitting the glass at 90 degree angles, so it should just go straight through, right? Whilst the top one is hitting part of the glass at an angle, so it should first be defracted downwards, and then upwards again when it exits the glass. Is that all I need to draw in there, or is there something else that I'm missing?
 
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phosgene said:

Homework Statement



White light is incident on a sheet of glass as shown below. Complete the ray tracing diagram.

physicsdiagram.jpg


Homework Equations



n1(sinx)=n2(siny), where n = the refractive index of the medium.

The Attempt at a Solution



The ray on the bottom is hitting the glass at 90 degree angles, so it should just go straight through, right? Whilst the top one is hitting part of the glass at an angle, so it should first be defracted downwards, and then upwards again when it exits the glass. Is that all I need to draw in there, or is there something else that I'm missing?
The correct word is 'refracted'.

The top beam is refracted towards the normal in going from air to glass. How about from glass to air?
 
SammyS said:
The correct word is 'refracted'.

The top beam is refracted towards the normal in going from air to glass. How about from glass to air?

Hmm, when it exits the glass, it would be refracted downwards again, wouldn't it?
 
SammyS said:
The top beam is refracted towards the normal in going from air to glass. How about from glass to air?

phosgene said:
Hmm, when it exits the glass, it would be refracted downwards again, wouldn't it?
What is the reason for thinking that? I.e., with respect to the normal in what direction (away from or towards the normal?) would it be refracted, in going from glass to air?
 
Redbelly98 said:
What is the reason for thinking that? I.e., with respect to the normal in what direction (away from or towards the normal?) would it be refracted, in going from glass to air?

Since the refractive index of glass is higher than that of air, the angle of refraction will be higher than the angle of incidence. And for that to happen, the ray would have to move downwards. Is this correct?
 
phosgene said:
Since the refractive index of glass is higher than that of air, the angle of refraction will be higher than the angle of incidence. And for that to happen, the ray would have to move downwards. Is this correct?

Yes - but better to say deflected down rather than move down.

The lead of your question referred specifically to white light. I wonder if you were supposed to show the formation of a spectrum due to dispersion?
 
phosgene said:
Since the refractive index of glass is higher than that of air, the angle of refraction will be higher than the angle of incidence. And for that to happen, the ray would have to move downwards. Is this correct?
Yes. (I just wanted to make sure you had the reasoning in mind -- it's easy to guess when there are just two choices, and other people are questioning your first answer :smile:)

PeterO makes a good point -- it's better to say "refracted downward" (as you had earlier) or deflected downward.
 
Last edited:
PeterO said:
Yes - but better to say deflected down rather than move down.

The lead of your question referred specifically to white light. I wonder if you were supposed to show the formation of a spectrum due to dispersion?

I get confused with all the different words in optics. Thanks for the correction :) And I'm not sure, I was wondering this myself, but the textbook I'm using doesn't go into that much, so I'm assuming that it's not necessary.

Thanks everyone!
 
phosgene said:
I get confused with all the different words in optics. Thanks for the correction :) And I'm not sure, I was wondering this myself, but the textbook I'm using doesn't go into that much, so I'm assuming that it's not necessary.

Thanks everyone!

In case you do need to consider dispersion - a good key for the two ends of the spectrum is

Red - rare
Violet - violent

The red rarely moves - meaning, it is deflected the least
The violet moves violently - meaning it is deflected the most.

Peter
 
  • #10
phosgene said:
Thanks everyone!
You're welcome!
PeterO said:
In case you do need to consider dispersion - a good key for the two ends of the spectrum is

Red - rare
Violet - violent

The red rarely moves - meaning, it is deflected the least
The violet moves violently - meaning it is deflected the most.

Peter
Or if you're an old-timer, just picture the album cover from Dark Side Of The Moon -- and remember that red is the top ray.

cover_2213172112008.JPG
 
  • #11
PeterO said:
In case you do need to consider dispersion - a good key for the two ends of the spectrum is

Red - rare
Violet - violent

The red rarely moves - meaning, it is deflected the least
The violet moves violently - meaning it is deflected the most.

Peter

Thanks, I'll keep that in mind :)
 

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