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Author:  hatari [ Wed Jul 25, 2007 2:22 am ]
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Hi Bill,

Think of composits (composite materials). eg vehicle wind screen glass or reflective building glass. The refractive index is very very important for optical quality requirements.

Sorry don't have a reference for this.

Hatari

Author:  Doos [ Wed Jul 25, 2007 8:23 am ]
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Hi,

As requested, here is the updated image with the refracted green line bending away from the normal ("NO").
Image

I left the intensity the same (will be mentioned in the text).

Author:  RAW rocks [ Wed Jul 25, 2007 10:30 am ]
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Thank you so much Doos, every little bit helps, in my case anyway.

Roberta

Author:  Barbara O. Ellis [ Wed Jul 25, 2007 12:00 pm ]
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Doos ... Dumb question #634: As long as the refracted light isn't actually ON the normal, by definition isn't it bending AWAY from the normal? :?:

Author:  Doos [ Wed Jul 25, 2007 1:24 pm ]
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Hi,

That depends on where the light is coming from and where it is traveling to.
Lets take water and air as our two media.

When light travels from air into water, the light will bend towards the normal.
When light travels from water into air, the light will bend away from the normal.

Hope that helped a bit.

Author:  JB [ Wed Jul 25, 2007 2:33 pm ]
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Hi MoDo,
If it helps, go back to the original diagram that started the quiz. Take a straight edge of some sort and place it parallel right along side the green arrow in the center figure, following the path through the hemisphere.

You will see as the light exits the denser glass to the less dense air it is bending toward the normal. In the corrected version above using the same demonstration, you will see that the path of light has bent away from the normal.

Author:  Barbara O. Ellis [ Wed Jul 25, 2007 4:21 pm ]
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D'uh! #-o Okay ... you look at it as if the line is continuing straight! My bad :oops: .

Say, didn't I study this about two years ago? 8)

Author:  cnl [ Wed Jul 25, 2007 5:33 pm ]
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I think also that for practical reasons you should draw a faceted gemstone lying on top of the prism demonstrating the denser material, it looks weird looking at this without the stone being examined... for me the important parts are the incident ray of light and the behaviour of the light in correlation to the imagined N-O line due to the denser material being observed... and what we see here is a diagram missing a piece of stone. :) I love stones, i need to see them everywhere ehehhehehe.... but remember, the angle of the incident ray of light equals the angle of the reflected ray of light... so you should draw a red line bent at the same angle on the opposite side.

...but once again i might not know what i am talking about at this hour... please be advised that

Author:  JB [ Wed Jul 25, 2007 6:17 pm ]
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Morning Dove wrote:
D'uh! #-o Okay ... you look at it as if the line is continuing straight! My bad :oops: .

Say, didn't I study this about two years ago? 8)

Yes you did MoDo. In the Diamonds course as well as briefly in the Liddecoat manual.

Feel free to invoke the Einstein rule contained in the highlighted portion of this passage: :wink:

One of my favorite stories is about Albert Einstein. One day a visitor stopped by to chat. As the visitor departed, the need arose to get Einstein’s telephone number. The visitor was surprised to see Einstein walk over to the telephone book and look up his own telephone number. When asked why he did not know his own number, he responded, "My dear boy, I have so many things to remember. I never bother to memorize anything that I can easily look up."

And now...JB's Theory of Relativity.
"Our ability to comprehend and utilize information is directly related to it's useful application in our everyday activities."

Author:  Barbara O. Ellis [ Wed Jul 25, 2007 6:35 pm ]
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:lol: Yes, JB, I use that quote often! 8)

Author:  Doos [ Thu Jul 26, 2007 11:42 am ]
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Hi demantoid,

It works the same if you put a gemstone on top, aslong as the refractive index of the gemstone is smaller than the hemicylinder.

Hi JB,

That quote is great, but following that logic .. why remember that ruby is red or snails taste good with garlick?
I agree that we need to remember a lot and that sometimes you could easily grab for a book and get the formula. But if you have no clue where to look, you will not find it fast.

When I was studying for the appraisal course, some of the onhands exam questions were about books. They will show you a snippet of a book (the binding side) and ask things like "who wrote that?" etc.
If you don't know what you are doing, the Einstein quote is not valid.
He knew in which book the answer was to be found.

It is perfectly fine to think about it as "why do I need that knowledge".
I can however think of more than a few reasons why you should atleast understand it.
(not aimed at you personally as I know you do).

There is a titbit knowledge that at a certain angle incidence light will be completely polarized in the plane of the object it reflects off.
If it wasn't for someone thinking about that, the Brewster Angle Meter never saw the light of day.

Thinking about these topics could maybe one day result in handy new tools like visual optics.

Author:  valeria102 [ Fri Jul 27, 2007 5:15 pm ]
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Doos wrote:
Hi Valeria,

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



Sorry... the thread slipped away from sight.

I meant to ask:

- why isn't any change in the light direction when passing from air into the other medium (glass).

and

- does the dotted green line have a story beyond refraction? As far as remember, this partial reflection accounts for imperfection in any real-world surfaces and/or imperfectly parallel light beams, effects that aren't part of discussion refraction as a theoretical model, unless one wants to make them so.

Author:  Doos [ Sat Jul 28, 2007 6:43 am ]
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Hi,

Quote:
why isn't any change in the light direction when passing from air into the other medium (glass).

There is, it bents towards the normal.

Quote:
does the dotted green line have a story beyond refraction? As far as remember, this partial reflection accounts for imperfection in any real-world surfaces and/or imperfectly parallel light beams, effects that aren't part of discussion refraction as a theoretical model, unless one wants to make them so.

It is of little importance to gemmology indeed (atleast as far as I know), I put it up there to show the difference between refraction and total internal reflection.

When total internal reflection happens, there is no refraction out (well maybe evanescent waves, but we can neglect that here).
While with refraction, the incident light is split into two parts. That is one of the key differences between total internal reflection and the reflection that accompanies refraction.
I somewhere read a phrase "total refraction" in the same context, which is of course someones enthusiasm in trying to introduce a new phenomenon.

Author:  cnl [ Sat Jul 28, 2007 9:26 am ]
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:?: While with refraction, the incident light is split into two parts.

In two parts? I have been tought (well I have bad memory so dont blame me tutors) that when a ray of light (i believe we are talking about the visible spectrum of wavelength here) is refracted its wavelengths are refracted into several components (associated with the familiar colors seen in your spectroscope)... what are these two parts you are talking about... you seem to confuse me alot...

Author:  Doos [ Sat Jul 28, 2007 10:00 am ]
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Hi,

The two parts I am refering to are the refracted and the reflected parts.
Of course if we were to loupe the refracted part, other things are going on .. as like you described.

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