New Mineral Named After GIA’s John Koivula
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 Post subject: filter fun
PostPosted: Tue Apr 29, 2008 12:57 pm 
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Quiz time!

Most colored gems act as color filters, subtracting some colors (selective absorption) while passing other colors through (selective transmission). Well I have here some actual color filters... not high quality, just some ones to play around with. The filters are described in this pdf file. The file describes rectangular sheets, but my filters are actually circular... the perfect size for setting on the coverglass of a D-cell maglite flashlight. The transmission spectrum of each filter is given in the linked pdf file. The color of each filter is as follows: red, green, blue, yellow, magenta (reddish-blue or bluish red), and cyan (greenish-blue or bluish-green).

I describe three experiments below, asking several questions about each. Lists of possible answers are given somewhere in the discussion previous to each question.

The first person who posts correct answers to all questions wins the filter set.


The answers to the first eight questions below can be chosen only from the following list: red, green, blue, yellow, magenta, cyan, white, black . Black should be chosen even when an exceptionally bright white light might cause some color to transmit through.

First we consider an experimental setup, where two filters with different colors are put in front of a flashlight's output. What color light is transmitted through overlapping...

1. ...red and magenta filters?

2. ...cyan and magenta filters?

3. ...yellow and magenta filters?

4. ...green and magenta filters?

5. ...blue and yellow filters?


Next we consider a new experimental setup, where the spots from two flashlight beams overlap on a white screen. A color filter is placed in front of one flashlight's output, and a second color filter is placed in front of the other flashlight's output. What color spot is seen on the screen when the following filters are chosen?

6. red and blue.

7. red and green.

8. blue and yellow.


The answers to questions 9 - 11 can be chosen only from the following list: yellow, magenta, cyan, blue

Now we consider a new experimental setup, where a flashlight is used to illuminate a ripe banana. A color filter is placed in front of this flashlight's output. What color filter will make the banana appear...

9. ...under-ripe, so that you think you have to wait a week before eating it.

10. ...perfectly ripe, so its time to eat.

11. ...over-ripe, so that you think it is time to throw the banana away.

12. ...a color not typically seen on a banana. Don't know if you want to eat a banana with that color.


Last edited by Brian on Tue Apr 29, 2008 2:24 pm, edited 1 time in total.

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 Post subject:
PostPosted: Tue Apr 29, 2008 2:22 pm 
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Ok, Brian, I'll be brave and give it a try first, as long as you promise not to laugh too hard. :D

1- Red
2- Blue
3- Orange
4- Blue
5- Green
6- Looks purple so possibly Magenta?
7- Yellow
8- White
9- Cyan
10- Yellow
11- Magenta
12- Blue

_________________
Crystal :smt086

Quantum Mechanics...the dreams stuff is made of. :smt047


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PostPosted: Tue Apr 29, 2008 2:31 pm 
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hi Crystal

Orange and purple are not allowed choices for questions 1 - 8, so those are definitely wrong. Some others are wrong, somewhere around half. :D


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PostPosted: Tue Apr 29, 2008 3:48 pm 
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1. red
2. blue
3. black
4. black
5. black
6. magenta
7. yellow
8. white
9. cyan
10. yellow
11. magenta
12. blue

I'm pretty sure some of those are wrong. I always have a hard time with additive/subtractive color in my head. :)


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PostPosted: Tue Apr 29, 2008 3:57 pm 
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About a quarter are incorrect. Looks like this quiz won't last long :roll:


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PostPosted: Tue Apr 29, 2008 4:06 pm 
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Ah, I'm revising a few. ;) Silly me.

1. red
2. blue
3. red
4. black
5. black
6. magenta
7. yellow
8. white
9. magenta
10. yellow
11. blue
12. cyan


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PostPosted: Tue Apr 29, 2008 4:28 pm 
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Better, but still not all correct.


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PostPosted: Tue Apr 29, 2008 7:50 pm 
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Don't know how I did that... swapped 9 and 12.

My answers (with analysis):

1. red
*red pass filter blocks G and B, magenta pass filter blocks G

2. blue
*cyan pass filter blocks R, magenta pass filter blocks G

3. red
*yellow pass filter blocks B, magenta pass filter blocks G

4. black
*green pass filter blocks B and R, magenta pass filter blocks G

5. black
*blue pass filter blocks R and G, yellow pass filter blocks B

6. magenta
*missing the G component of white RGB

7. yellow
*missing the B component of white RGB

8. white
*yellow is composed R and G, so add B to get white RGB

9. cyan
*RGB light hits cyan filter, filter blocks R, banana absorbs B and reflects G light to eye (banana appears green)

10. yellow
*RGB light hits yellow filter, filter blocks B, banana reflects R and G light to eye (banana appears yellow)

11. blue
*RGB light hits blue filter, filter blocks R and G, banana absorbs B, no light returns to eye (banana appears "black")

12. magenta
*RGB light hits magenta filter, filter blocks G, banana absorbs B and reflects R light to eye (banana appears red, which isn't really that weird)


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PostPosted: Tue Apr 29, 2008 8:12 pm 
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:smt041 :smt038 We have a winner! :smt038 :smt041
:smt111 :smt111 :smt111

... after three tries :wink:

Good color analysis :smt099

Karim, pm me an address and you'll have the filters in a couple weeks. Then you can do the experiments for yourself, and verify the results!

oh yeah, I thought about the red banana, because I knew little, dark red bananas exist. But this would be a big, bright red banana. Besides, those dark red bananas take forever to ripen, and you can't tell easily when they are ripe.


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PostPosted: Tue Apr 29, 2008 8:35 pm 
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Heck, I didn't even realize I was going to win anything other than lasting fame. :shock: I probably should have read the opening post more thoroughly...


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PostPosted: Tue Apr 29, 2008 9:19 pm 
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hi
ill try :wink:

1.red
2. blue
3.red
4. black
5. black

6. magenta
7.yellow
8. white

9. cyan
10. blue (this one yellow )
11. yellow( this one blue )
i was in a rush to post and mixed them up on my scap paper
12. magenta or red

oh man i was working on it and come back and find out someone won already :x , well it was fun :lol: i mixed up the answers in my answers of the last three.
Congrads Gem-N00b :smt041


Last edited by dragonstek on Wed Apr 30, 2008 8:18 am, edited 1 time in total.

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PostPosted: Tue Apr 29, 2008 11:04 pm 
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Well just check your answers against Karim's. He gives a really good description of why each answer is the way it is.


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