## Optics B/C

Unome
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### Re: Optics B/C

meierfra wrote:This is a question for those of you that have done Optics already at an invitational. I have to run Optics next month with 12 teams in 50 minutes (twice). I can't do it with one LSS box. If I put the 2 LSSs near each other and stagger them, then when one team starts, they can see what the other team is doing. If I put the 2 LSSs on opposite sides of the room, then I worry about getting consistent directions and measuring, etc.
How has it been done at the invitationals you've attended? Do most of the teams take most of their 4 minutes?

What if you took a piece of plywood or something and just placed it down as a divider between the two boxes?
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### Re: Optics B/C

Unome wrote:
meierfra wrote:This is a question for those of you that have done Optics already at an invitational. I have to run Optics next month with 12 teams in 50 minutes (twice). I can't do it with one LSS box. If I put the 2 LSSs near each other and stagger them, then when one team starts, they can see what the other team is doing. If I put the 2 LSSs on opposite sides of the room, then I worry about getting consistent directions and measuring, etc.
How has it been done at the invitationals you've attended? Do most of the teams take most of their 4 minutes?

What if you took a piece of plywood or something and just placed it down as a divider between the two boxes?

I usually run with 2 LSSs on tables abour 4-6 feet apart. Teams are generally too concerned with their own LSS to look at the other one. Even if they did, it's hard to gain much advantage since everyone uses different techniques and tools. Many teams take far less than 4 minutes.

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### Re: Optics B/C

I'm having a great deal of difficulty finding things on absorption spectra and whatnot. Does anyone have any resources that would be helpful?
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### Re: Optics B/C

antoine_ego wrote:I'm having a great deal of difficulty finding things on absorption spectra and whatnot. Does anyone have any resources that would be helpful?

A good place to always start is Wikipedia: https://en.wikipedia.org/wiki/Absorption_spectroscopy

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### Re: Optics B/C

Hey guys, just wondering what most of y'all are planning on doing the laser shoot. Are y'all planning on using all five mirrors and the bonus mirror? And do you think the bonus mirror is even worth it since it is just 5 points (it seems like it is a small reward for the risk)?
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### Re: Optics B/C

I don't think there is anything on absorption spectra here but there is quite a bit of other stuff.
https://www.newport.com/resourceListing ... y%3AOptics
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### Re: Optics B/C

hi, on the rules it talks about reference materials needing to be secured in a 3 ring binder

these reference materials can be used during both the written portion and the laser shoot part, right?

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### Re: Optics B/C

impossiblesphere wrote:hi, on the rules it talks about reference materials needing to be secured in a 3 ring binder

these reference materials can be used during both the written portion and the laser shoot part, right?

Surprisingly the rules never explicitly state that the binder can be used during all parts of the competition, but I would assume that this is true considering that has for other physics events (compound, time, etc).
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### Re: Optics B/C

jkang wrote:
impossiblesphere wrote:hi, on the rules it talks about reference materials needing to be secured in a 3 ring binder

these reference materials can be used during both the written portion and the laser shoot part, right?

Surprisingly the rules never explicitly state that the binder can be used during all parts of the competition, but I would assume that this is true considering that has for other physics events (compound, time, etc).

Under 2b it says "Competitors may bring any measuring tools, premade templates, writing utensils and any type of calculators for use during any part of the competition."
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### Re: Optics B/C

jkang wrote:Here's my optics test from the recent UT-Austin invitational (key). If you have any questions about it, feel free to PM or email me!

I was looking at this test and am stuck on problem 5. How do you find the focal length of a lens without knowing the radii of curvature? Sorry if it's a bit of a dumb question, I'm new to this event.

Thanks
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### Re: Optics B/C

Bob_117 wrote:
jkang wrote:Here's my optics test from the recent UT-Austin invitational (key). If you have any questions about it, feel free to PM or email me!

I was looking at this test and am stuck on problem 5. How do you find the focal length of a lens without knowing the radii of curvature? Sorry if it's a bit of a dumb question, I'm new to this event.

Thanks

This is a thick lens problem, not thin lens. The approach will be different.

The problem asks for the focal length of the lens. We are given the following information.
Lens power on both sides: 2.25 diopeters
Index of refraction: 1.5
Thickness, or separation between the lens' sides: 10 cm or .1 meters.

I know that, with the given information, you can find the focal length of the lens with Gullstrand's Equation found here: http://hyperphysics.phy-astr.gsu.edu/hbase/geoopt/Gullcal.html#

P is the lens' power, $P_1$ is the right side's power, $P_1$ is the right side's power, d is the thickness, and n is the index of refraction.

When you know this, the problem is simple.
$P=2.25+2.25-(2.25)(2.25)(\frac{0.1}{1.5})$
This works out to a power of 4.1625 diopeters. The focal length is the reciprocal of the power, so the final answer is 24 centimeters.

Thick lens is not a topic covered in the rules, but you should be familiar with it if you want to succeed.
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### Re: Optics B/C

Thanks Oddrenaline.
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### Re: Optics B/C

jonboyage wrote:Under 2b it says "Competitors may bring any measuring tools, premade templates, writing utensils and any type of calculators for use [u]during any part of the competition."

I interpreted this as things other than the binder, since 2a states that as "reference material," whereas 2b lists other things.
Bob_117 wrote:I was looking at this test and am stuck on problem 5. How do you find the focal length of a lens without knowing the radii of curvature? Sorry if it's a bit of a dumb question, I'm new to this event.
Thanks

As 0ddrenaline stated, this question should be approached as a thick lens problem through Gullstrand's equations. Although it's not explicitly stated in the rules as a topic, it can be implicitly included under lenses (at least that's where I chose to include it when writing this test). And for full points (accounting for significant figures), the answer would be 24.0 cm, not just 24 cm.
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### Re: Optics B/C

Hey Guys,

I've heard that for optics we get a paper as the base we are allowed to draw on to make our angular geometry easier? Is this true? I don't see it in the 2017 rules but when looking up event info I saw something of the sort? Does anyone know?

Thanks in advanced,
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### Re: Optics B/C

So what exactly is an optic? I was a little confused.
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