Ray tracing diagram for white light moving through glass

1. Jan 13, 2012

phosgene

1. The problem statement, all variables and given/known data

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

2. Relevant equations

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

3. 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?

2. Jan 13, 2012

SammyS

Staff Emeritus
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?

3. Jan 14, 2012

phosgene

Hmm, when it exits the glass, it would be refracted downwards again, wouldn't it?

4. Jan 15, 2012

Redbelly98

Staff Emeritus
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?

5. Jan 16, 2012

phosgene

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?

6. Jan 16, 2012

PeterO

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?

7. Jan 16, 2012

Redbelly98

Staff Emeritus
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 )

PeterO makes a good point -- it's better to say "refracted downward" (as you had earlier) or deflected downward.

Last edited: Jan 16, 2012
8. Jan 17, 2012

phosgene

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!

9. Jan 17, 2012

PeterO

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. Jan 17, 2012

Redbelly98

Staff Emeritus
You're welcome!
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.

11. Jan 17, 2012

phosgene

Thanks, I'll keep that in mind :)