Optics B/C

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Re: Optics B/C

Postby jkang » Sun Dec 25, 2016 6:21 pm

Tom_MS wrote:
Cloudia wrote:Hello :)
While I was expecting that my students would struggle with the state/national level theory (lasers, multiple lenses, etc) that the Cornell Invitational is known for, there were questions in which I can't see how they fit within any of this year's optics topics. Alternatively, is it common to see more topics thrown than expected?

I'm currently a student, but I'll give you my take. The Cornell invitational is known for writing odd tests in some events, so I'm sorry to say I wouldn't base your studying off of the experience there.
To reference this year's rules, "Optical Absorption Spectra: Film, chemicals, dyes" could be interpreted as analysis of energy levels as well as analysis of spectra. This leads to a need for understanding the energy and characteristics of photons as well as methods such as diffraction which can produce spectral lines.
Redshift was on previous years' rules I believe, but not this year. In this respect, Cornell seems to have simply failed at following the rules.

I'm a grad and I've written/proctored various tests at different levels of tournaments, so here's my take on it. While some subjects might be outside of the defined area, I think that one of the most important part of the rules is in 4.c.: "The competition must consist of at least two questions from each of the following areas". Now the way I interpret this line may be different from how others do, but when I write tests the first thing I generally do is make sure that I meet this quota. However beyond these 20 questions, I generally add questions that are not listed in the provided topics (for example, wave optics and some astronomy-related things) that I think are still important to know for the overall subject of optics. This doesn't go against the rules at all as far as I can see, as I am meeting the 20 question requirement, but just adding some new topics/questions of my own on top of that. Thus if I was currently competing in Optics, I wouldn't limit myself to knowledge of just the topics listed, but try to get as much breadth as possible in the subject, as other test-writers could always think the same way I do. Plus that's representative of the spirit of Science Olympiad - not just limiting knowledge to content that will be presented on a test, but to have kids explore a subject beyond what schools/classes regularly teach as well as diving into the subject as much as they can/want.

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Re: Optics B/C

Postby Tom_MS » Thu Dec 29, 2016 11:30 pm

True. Some rules have different wording but with optics you're right.

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Re: Optics B/C

Postby Fluorine » Sat Jan 07, 2017 7:08 am

Can someone check me back on this problem its a Doppler Shift one?

"A spaceship is moving away from an asteroid at a relative velocity of 2.8481 x 10^8 m/s. The spaceship sends a signal with a frequency of 5 x 10^6 Hz to a base located on the asteroid. What is the frequency of the signal measured by the base?"

I keep getting 2.56 x 10^6 Hz but the test key says the answer is 3.1225 x 10^7 Hz.
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Re: Optics B/C

Postby John Richardsim » Sat Jan 07, 2017 7:36 am

Fluorine wrote:Can someone check me back on this problem its a Doppler Shift one?

"A spaceship is moving away from an asteroid at a relative velocity of 2.8481 x 10^8 m/s. The spaceship sends a signal with a frequency of 5 x 10^6 Hz to a base located on the asteroid. What is the frequency of the signal measured by the base?"

I keep getting 2.56 x 10^6 Hz but the test key says the answer is 3.1225 x 10^7 Hz.

I jammed those numbers into an online doppler shift calculator and got your answer. Couldn't seem to figure out how to get their answer.
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Re: Optics B/C

Postby jkang » Sat Jan 07, 2017 9:14 am

Fluorine wrote:I keep getting 2.56 x 10^6 Hz but the test key says the answer is 3.1225 x 10^7 Hz.

Using hyperphysics and wolframalpha, I got 3.12*10^7 Hz if the spaceship moves towards the asteroid, rather than away from it - this follows common sense, as redshifting would lower frequency, whereas blueshifting would increase it. Looks like your proctor either misworded the question, or applied the wrong equation in his/her calculations of answers.
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Re: Optics B/C

Postby whyiamafool » Sun Jan 08, 2017 10:14 pm

Hello,

My team recently went to an invitational and found out that the TP (target point) was off 5 cm from the center line from that particular invitational. The team reviewed the rules once again and it says that event supervisors select a TP that is the same for all teams.

Does this mean that event supervisors can select a TP anywhere along the Target Wall?

Thanks.
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Re: Optics B/C

Postby Adi1008 » Sun Jan 08, 2017 10:26 pm

whyiamafool wrote:Hello,

My team recently went to an invitational and found out that the TP (target point) was off 5 cm from the center line from that particular invitational. The team reviewed the rules once again and it says that event supervisors select a TP that is the same for all teams.

Does this mean that event supervisors can select a TP anywhere along the Target Wall?

Thanks.


Yeah, it can be anywhere along the back wall
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Re: Optics B/C

Postby jonboyage » Sun Jan 08, 2017 10:28 pm

whyiamafool wrote:Hello,

My team recently went to an invitational and found out that the TP (target point) was off 5 cm from the center line from that particular invitational. The team reviewed the rules once again and it says that event supervisors select a TP that is the same for all teams.

Does this mean that event supervisors can select a TP anywhere along the Target Wall?

Thanks.


Yes, the proctor can make the target anywhere along the target wall. So far, every invitational I have been to this year has had the target off-center. The farthest I've seen so far is 9cm off-center
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Re: Optics B/C

Postby chalker » Sun Jan 08, 2017 10:42 pm

whyiamafool wrote:Hello,

My team recently went to an invitational and found out that the TP (target point) was off 5 cm from the center line from that particular invitational. The team reviewed the rules once again and it says that event supervisors select a TP that is the same for all teams.

Does this mean that event supervisors can select a TP anywhere along the Target Wall?

Thanks.


Read rule 3.f. very carefully. It says one of the marks is the TP, It does NOT say a particular mark is the TP.

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Re: Optics B/C

Postby egbertghost » Mon Jan 09, 2017 9:37 pm

Fluorine wrote:Can someone check me back on this problem its a Doppler Shift one?

"A spaceship is moving away from an asteroid at a relative velocity of 2.8481 x 10^8 m/s. The spaceship sends a signal with a frequency of 5 x 10^6 Hz to a base located on the asteroid. What is the frequency of the signal measured by the base?"

I keep getting 2.56 x 10^6 Hz but the test key says the answer is 3.1225 x 10^7 Hz.


I asked my cousin (an Astronomy Harvard professor) said to use the Red Doppler Shift formula, and then I got the same answer as you. The test writer probably did something wrong lol. Good luck!
Last edited by egbertghost on Mon Jan 09, 2017 9:42 pm, edited 1 time in total.
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Re: Optics B/C

Postby egbertghost » Mon Jan 09, 2017 9:37 pm

Fluorine wrote:Can someone check me back on this problem its a Doppler Shift one?

"A spaceship is moving away from an asteroid at a relative velocity of 2.8481 x 10^8 m/s. The spaceship sends a signal with a frequency of 5 x 10^6 Hz to a base located on the asteroid. What is the frequency of the signal measured by the base?"

I keep getting 2.56 x 10^6 Hz but the test key says the answer is 3.1225 x 10^7 Hz.


I asked my cousin (an Astronomy Harvard professor) he said to use the Red Doppler Shift formula, and then I got the same answer as you. The test writer probably did something wrong lol. Good luck!
CyFalls/MIT/Anthony/District/Regional/State
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Crime Busters:11/6/6/x/

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Re: Optics B/C

Postby kenniky » Tue Jan 10, 2017 12:03 am

Hi,

does anyone know what "films, chemicals, dyes" means in 4.d.x? Do we have to have the absorption spectra for these materials; if so, how comprehensive does it need to be? I'm not having much luck

Thanks.
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Re: Optics B/C

Postby bearasauras » Wed Jan 11, 2017 4:51 am

egbertghost wrote:
Fluorine wrote:Can someone check me back on this problem its a Doppler Shift one?

"A spaceship is moving away from an asteroid at a relative velocity of 2.8481 x 10^8 m/s. The spaceship sends a signal with a frequency of 5 x 10^6 Hz to a base located on the asteroid. What is the frequency of the signal measured by the base?"

I keep getting 2.56 x 10^6 Hz but the test key says the answer is 3.1225 x 10^7 Hz.


I asked my cousin (an Astronomy Harvard professor) he said to use the Red Doppler Shift formula, and then I got the same answer as you. The test writer probably did something wrong lol. Good luck!


I think the test writer has the correct answer. If you're using the typical Doppler Shift equation f = f_source * v / (v-v_source), you haven't taken into consideration that the spaceship has a very high relative velocity (close to the speed of light). Using the Doppler Shift equation here will get us an answer of 2.56 x 10^6 Hz.

To get to correct answer, we need to take relativistic effects into consideration by using the Relativistic Doppler Shift equation:
f = f_source * Sqrt(1 - (v_source/c)^2) / (1- (v_source/c))
Using this equation, we get 3.1225 x 10^7 Hz (you can test it out yourself at the bottom of hyperphysics. When the v_source is small compared to the speed of light, this equation can be approximated as the typical Doppler Shift equation that you were using.

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Re: Optics B/C

Postby jonboyage » Wed Jan 11, 2017 1:04 pm

bearasauras wrote:
egbertghost wrote:
Fluorine wrote:Can someone check me back on this problem its a Doppler Shift one?

"A spaceship is moving away from an asteroid at a relative velocity of 2.8481 x 10^8 m/s. The spaceship sends a signal with a frequency of 5 x 10^6 Hz to a base located on the asteroid. What is the frequency of the signal measured by the base?"

I keep getting 2.56 x 10^6 Hz but the test key says the answer is 3.1225 x 10^7 Hz.


I asked my cousin (an Astronomy Harvard professor) he said to use the Red Doppler Shift formula, and then I got the same answer as you. The test writer probably did something wrong lol. Good luck!


I think the test writer has the correct answer. If you're using the typical Doppler Shift equation f = f_source * v / (v-v_source), you haven't taken into consideration that the spaceship has a very high relative velocity (close to the speed of light). Using the Doppler Shift equation here will get us an answer of 2.56 x 10^6 Hz.

To get to correct answer, we need to take relativistic effects into consideration by using the Relativistic Doppler Shift equation:
f = f_source * Sqrt(1 - (v_source/c)^2) / (1- (v_source/c))
Using this equation, we get 3.1225 x 10^7 Hz (you can test it out yourself at the bottom of hyperphysics. When the v_source is small compared to the speed of light, this equation can be approximated as the typical Doppler Shift equation that you were using.


Using hyperphysics, you have to specify a negative relative velocity when plugging it into their equation since the spaceship is moving away. They specify this, saying "for red shift calculations, use negative velocities." We know it must be red shift since the spaceship is moving away which would elongate the wavelengths and decrease the frequency.

Using the positive velocity, you get 3.1225*10^7 Hz but using the negative velocity, you get .80064*10^6 Hz, which makes more sense.
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Re: Optics B/C

Postby meierfra » Wed Jan 11, 2017 6:28 pm

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?


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