New Mineral Named After GIA’s John Koivula
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 Post subject: Spot the error
PostPosted: Tue Jul 24, 2007 12:06 pm 
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Hi,

I was making a picture to illustrate total internal reflection for the gemology project.
When I reviewed it I noticed a slight but noticable error.

The light is traveling from air into a hemicylinder (made of lets say glass) to air again.

Can you spot the error?
Winner gets everlasting fame.

Image


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PostPosted: Tue Jul 24, 2007 12:15 pm 
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This is just a guess, but if it is total internal reflection then shouldn't the green line in the center not be going all the way through.


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PostPosted: Tue Jul 24, 2007 12:22 pm 
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Hi,

You are warm and cold.
The green line will both refract out and reflect back, so if your answer is that it doesn't reflect, then .. no, not the correct answer.


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PostPosted: Tue Jul 24, 2007 1:20 pm 
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Sheesh! Can't tell.. Would have two Qs

1. No refraction?

2. The partial reflection below the CR... isn't that usually assumed away from the bare definition? I.e. if combining more than one effect...


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PostPosted: Tue Jul 24, 2007 1:40 pm 
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Hi Valeria,

The laws of refraction are the key here.
Could you rephrase you questions?


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 Post subject: stab in the dark
PostPosted: Tue Jul 24, 2007 2:31 pm 
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absolutely no idea about these things, but if the green line is partially reflected, shouldnt the line that does not reflect but travels through also be a partial intensity?represented as a dotted line like the reflected line?
Just a stab in the dark from a newbie :wink:


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PostPosted: Tue Jul 24, 2007 2:38 pm 
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The exiting green line should be bent away from the normal.


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PostPosted: Tue Jul 24, 2007 2:40 pm 
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Hi sticky,

Very well spotted, true. But not the answer I was looking for.
So I guess that makes two errors. One solved.

Eternal fame to sticky for logical thinking.


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PostPosted: Tue Jul 24, 2007 2:42 pm 
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Hi Bill,

Good eye you have, all solved!

When light travels from an optically denser to an optically rarer medium, the light bends away from the normal .. not towards it as I mistakenly illustrated.

Another hall of fame spot for Dr. Hanneman.


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PostPosted: Tue Jul 24, 2007 3:40 pm 
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Doos,

Will you post the corrected drawing or let me know where to find it so that I can understand better.


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PostPosted: Tue Jul 24, 2007 3:49 pm 
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Hi,

I will create an updated one tomorrow.


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PostPosted: Tue Jul 24, 2007 4:55 pm 
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Hi Raw Rocks,

Here is a link to help you understand refraction.

http://www.ulwaziproject.co.za/f3scienc ... ction.html

This law is what helps bring out the "luster" in gem stones thus dimensions are important when faceting.

Here is a great website related to gems and refractive index (plus more):

http://www.khulsey.com/jewelry/gemstone ... index.html

Hope it helps.

Hatari


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PostPosted: Tue Jul 24, 2007 6:06 pm 
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thanks hatari,

The second link was especially helpful as it used gems as examples and was not overly technical.


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PostPosted: Tue Jul 24, 2007 8:49 pm 
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Can anyone explain those refractive index values for metals?


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PostPosted: Tue Jul 24, 2007 10:35 pm 
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ooo, I'm so mad I missed this one.

I ask qualitative questions just like these on my refraction exam (shhh, don't tell my students). Only in my questions, I usually include a phrase similar to the following: The diagram below may not exhibit any errors, may exhibit a single error, or may exhibit multiple errors. How many errors can you spot in the diagram?


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