August 24:—SAN ANTONIO, TEXAS: Retail show; Southwest Gem and Mineral Society of San Antonio; Sat. 10-5
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PostPosted: Fri Nov 30, 2007 2:25 pm 
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You're welcome,

May I have the details of your tourmaline supplier now? :)

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PostPosted: Fri Nov 30, 2007 2:36 pm 
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hi

i dont know if im right but ill try shouldnt the light be reflected 90 degrees out the top :oops: and if its wrong :shock:
and if its wrong :shock: ive got to keep working on this :x


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 Post subject: Sorry Doos!
PostPosted: Fri Nov 30, 2007 2:46 pm 
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Sorry Doos!

Check pm....

Lyresa


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PostPosted: Fri Nov 30, 2007 2:47 pm 
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See Ravuris, we assumed the wave had already passed through the grid instead of considering the grid a polarizing filter with the long chain molecules aligned vertically creating a horizontal polarization axis. Since the light wave was already linearly polarized N/S it was absorbed by the vertically orientated polarized grid. Nothing left to exit the grid and no E/W vibrational waves to pass through.

BAH!


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PostPosted: Fri Nov 30, 2007 3:10 pm 
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Heh, indeed.

I must confess that I discovered this only recently myself as the "picket fence" example is so easy to understand .. although it is wrong, it is very intuitive.

In most textbooks you will see a drawing in the line of:
Image
Which merely shows the "pass-through" direction. In this case the lightwaves vibrating in the north-south direction are allowed to pass through.

For some odd reason we translate that to a "picket-fence" or a "venetian blind" as in the following image:
Image

While in fact the wires should be orientated east-west to allow a lightwave vibrating in the north-south direction to pass through:
Image

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 Post subject: So was I right????
PostPosted: Fri Nov 30, 2007 3:13 pm 
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So was I RIGHT in my guess? If so, I'm gonna DANCE 'cos I understand it better....if not, I'll mutter off to my corner in the library again....

Lyresa


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PostPosted: Fri Nov 30, 2007 3:16 pm 
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Hi,

The original image was indeed wrong, the lightwave should not have passed through.

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 Post subject: Doo Waa Cha Cha!
PostPosted: Fri Nov 30, 2007 3:36 pm 
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:smt035 :smt026 :smt111

Lyresa


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PostPosted: Fri Nov 30, 2007 9:01 pm 
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Lyresa, you would love to join us for the chats on Saturday, and I'm happy to say that because I've attended them for so many years, when I saw that drawing I realized the slats went the wrong way. You get to ask all the questions you want right then and there which allows you to fill in the gaps in understanding these concepts. It's been extremely helpful to me, so if you can make it at 4pm tomorrow I highly recommend you join us. :D

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PostPosted: Sat Dec 01, 2007 5:12 am 
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Ahem...

If that's true, I spot a bit of a dilemma... I've just checked my course notes, chapter ten, pages three, eight, nine - and there are bound to be others. They all show diagrams of polarizing filters drawn with the 'picket-fence' analogy. Vertical slits, and vertical rays passing through them... :shock:

Let's just say I'm glad I'm not doing my exam tomorrow - It'd be hard to know what to draw on my answers paper, wouldn't it? :o In any case, can't this be considered a 'silent agreement'? A bit like in electricity you can talk about 'current flowing from + to -' instead of 'electrons moving from - to +'?

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PostPosted: Sat Dec 01, 2007 5:20 am 
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Keirkof wrote:
Ahem...

If that's true, I spot a bit of a dilemma... I've just checked my course notes, chapter ten, pages three, eight, nine - and there are bound to be others. They all show diagrams of polarizing filters drawn with the 'picket-fence' analogy. Vertical slits, and vertical rays passing through them... :shock:


i assume you're talking about Gem-A course.
Doos? at this point i'm getting curious.... :smt017
ciao

alberto


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PostPosted: Sat Dec 01, 2007 5:28 am 
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RAVIRUS wrote:
i assume you're talking about Gem-A course.
Doos? at this point i'm getting curious.... :smt017


Yup, I was refering to the Gem-A course.

I think the diagrams and Doos are probably both right. If you interpret the 'picket fence' not as an exact representation of the atomic structure, but merely as a conceptual representation. That would state 'this is a polarizing filter that only lets through vertically aligned light rays'. And not necessarily (even though it might usually mean) 'this material contains horizontal rows of atoms'. It's all how you interpret things, probably...

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PostPosted: Sat Dec 01, 2007 8:31 am 
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Hi,

I just checked my course notes and they say:
Quote:
It passes through a substance that allows only light vibrating in one direction to be transmitted. If we consider the polarisation direction of the filter to be 'north-south', then the light transmitted will be plane polarised in a 'north-south' direction.

Then they draw a diagram with the north-south direction indicated by a line with 2 arrows (like in one of my images). That is correct.
It indicates the polarisation direction, not the direction of the wires (which would run east-west). Of course they don't want to confuse everyone like I do, so I'm sure they left that out intentionally.

p.s.: note that they say "a substance", not in particular a wire-grid polarizer.
Polarization can be created by many means.
If you want to explore outside the course notes, you better get it right or you'll fail the exam.

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PostPosted: Sat Dec 01, 2007 5:53 pm 
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Maybe the "picket fence" analogy should be dropped from courses and textbooks?

After all, it isn't a very good analogy in the first place. It is a simple visualization for when light polarization is parallel or perpendicular to the "picket fence", but it certainly doesn't predict or explain what happens when light polarization is tilted at an arbitrary angle with the "picket fence".

But to be fair, I've seen this analogy used in high school physics texts from the 1920s.


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 Post subject: Light Waves/Polarization
PostPosted: Sat Dec 01, 2007 8:18 pm 
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Part of my problem grasping this concept is I never studied chemistry nor physics but sometimes I think maybe that was a blessing instead. I've grasped the concept of the wired polarizer now but all the rest of this is confusing me again!

Radio waves are a lot easier to understand - they are a LOT tamer!

Lyresa


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