## Optics B/C

MrGood
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Posts: 8
Joined: September 15th, 2016, 2:25 pm
Division: B
State: CA

### Re: Optics B/C

I haven't been able to find any good sources for the films chemicals and dies section of the absorbtion spectra topic, does anyone have good sources they know of or general inforation?

Member
Posts: 66
Joined: January 6th, 2017, 4:51 pm
State: PA
Location: Swarthmore College

### Re: Optics B/C

I'm interested in checking this again a little later in the season- what type of scores are people averaging on the LS? Additionally, how difficult has the barrier mirror typically been for you? i.e. at a convenient 45° angle vs. 180° away from the laser.
Lower Merion 2017
Subtitled: Revenge of the Non-Harriton

Placement Record:

Code: Islip | Conestoga | Tiger | Regionals | States
Out of: 61 | 42 | 36 | 37 | 36

Chemistry Lab: 9 | - | - | 4 | 4
Astronomy: 14 | - | 5 | 10 | 3
Material Science: 12 | 19 | 9 | 5 | 9
Optics: 14 | 7 | 3 | 4 | 2

breakingankles
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Posts: 12
Joined: November 15th, 2015, 9:36 pm
Division: C
State: TX

### Re: Optics B/C

The people doing it on my team are able to get close to a perfect score almost every time (all 5 mirrors + barrier mirror + very accurate). It's just the test that kills us....

kenniky
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Posts: 283
Joined: January 21st, 2016, 6:16 pm
State: MA
Location: ABRHS --> UMichigan

### Re: Optics B/C

Does anyone know what a minimum dispersion angle is? (not minimum deviation). it came up on a test we took

10. What is the index of refraction for an equilateral prism with a minimum dispersion angle of 30 degrees?
a. 1.50 b. 1.52 c. 1.58 d. 1.62

If you use the formula for minimum deviation you get 1.41. The answer is [hide]1.62[/hide]
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ericlepanda
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Posts: 51
Joined: February 9th, 2016, 2:53 pm
Division: C
State: IL

### Re: Optics B/C

How are some of you able to get the barrier mirror? Since it can be placed at any angle, isn't it impossible to use?
ntso
quack quack

jonboyage
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Posts: 102
Joined: December 13th, 2016, 8:32 am
State: PA

### Re: Optics B/C

How are some of you able to get the barrier mirror? Since it can be placed at any angle, isn't it impossible to use?
It is certainly not impossible to use. There are many different ways the barrier mirror can be placed, however the judge should not make it an impossible mirror, for example too close to any wall. There are a lot of interesting solutions that my partners and I have found for various barrier locations simply by trying out different ways the mirror can be placed. I would recommend playing around with an LSS that you can make for yourself if you don't have one already. There are some really good suggestions earlier in this thread. Good luck!
I was in a bin

Rustin '19
UPenn '23

gryphaea1635
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Posts: 33
Joined: April 4th, 2015, 4:04 pm
Division: C
State: MA
Location: touching my spaghet

### Re: Optics B/C

Hi guys,

Can someone explain how to solve this problem? It was on the question marathon (page 3 or 4 I think, kenniky's problem on angle of deviation in prisms)
Thanks!
Question:
In the prism below, α is 35° and θ is 19°. The prism has index of refraction 1.45 and is in a vacuum

What is the deviation?

(It was 19 degrees between the light ray and prism face, not the normal)

I tried finding the initial angle of refraction, and then using that to find the second angle of incidence out of the prism by making a triangle with the apex angle, the complementary of the second angle of incidence, and the complementary of the first angle of refraction. But then I got around 95 degrees as the angle of incidence within the prism, which doesn't make sense, and that's as far as I got haha.
Am I taking the right approach? What do?
ESKKEEEETTTIIITT

jkang
Member
Posts: 107
Joined: October 17th, 2014, 8:49 pm
State: TX

### Re: Optics B/C

Hi guys,
Can someone explain how to solve this problem? It was on the question marathon (page 3 or 4 I think, kenniky's problem on angle of deviation in prisms)
Thanks!
Question:
In the prism below, α is 35° and θ is 19°. The prism has index of refraction 1.45 and is in a vacuum
What is the deviation?

(It was 19 degrees between the light ray and prism face, not the normal)
I tried finding the initial angle of refraction, and then using that to find the second angle of incidence out of the prism by making a triangle with the apex angle, the complementary of the second angle of incidence, and the complementary of the first angle of refraction. But then I got around 95 degrees as the angle of incidence within the prism, which doesn't make sense, and that's as far as I got haha.
Am I taking the right approach? What do?
For future reference, inserting the image or linking to the original problem (here) can be useful for the visuals. In terms of solving the problem, refer to the last equation found on the Wikipedia for minimum deviation. Here iwould be 90-19=71 degrees, since we are calculating for the angle of incidence. We know that A[/] is 35 degrees, and n is 1.45. Plugging in these numbers, we find our angle of deviation to be 27.72 degrees (28 technically with the given significant figures), which seemed to have been the correct solution. You can probably derive this equation for yourself without too much difficulty through the use of Snell's law and arbitrary angles.
UT Austin '19
Liberal Arts and Science Academy '15

ericlepanda
Member
Posts: 51
Joined: February 9th, 2016, 2:53 pm
Division: C
State: IL

### Re: Optics B/C

How are some of you able to get the barrier mirror? Since it can be placed at any angle, isn't it impossible to use?
It is certainly not impossible to use. There are many different ways the barrier mirror can be placed, however the judge should not make it an impossible mirror, for example too close to any wall. There are a lot of interesting solutions that my partners and I have found for various barrier locations simply by trying out different ways the mirror can be placed. I would recommend playing around with an LSS that you can make for yourself if you don't have one already. There are some really good suggestions earlier in this thread. Good luck!
But how are you able to account for the mirror being at any angle? If they put a barrier mirror at a weird angle like (for example) 157 degrees, how would anyone be able to use it?
ntso
quack quack

0ddrenaline
Member
Posts: 117
Joined: May 21st, 2015, 6:36 pm
State: MI

### Re: Optics B/C

How are some of you able to get the barrier mirror? Since it can be placed at any angle, isn't it impossible to use?
It is certainly not impossible to use. There are many different ways the barrier mirror can be placed, however the judge should not make it an impossible mirror, for example too close to any wall. There are a lot of interesting solutions that my partners and I have found for various barrier locations simply by trying out different ways the mirror can be placed. I would recommend playing around with an LSS that you can make for yourself if you don't have one already. There are some really good suggestions earlier in this thread. Good luck!
But how are you able to account for the mirror being at any angle? If they put a barrier mirror at a weird angle like (for example) 157 degrees, how would anyone be able to use it?
Work backwards. Find the angle from your target location to the barrier, then reflect off from the barrier to find the location where you should place the mirror.