Optics B/C

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Re: Optics B/C

Post by Schrodingerscat » February 7th, 2012, 5:35 pm

blue cobra wrote:The Wolfram page repeatedly refuses to load on my computer. Would someone be so kind as to fill me in?
To find the lens power to correct farsighted vision:
Find the inverse of the desired near focus distance and subtract the inverse of the uncorrected near focus distance.

To correct nearsighted vision:
Take the inverse of the uncorrected far focus point and reverse the signs to find the required lens power to focus at infinity.

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Re: Optics B/C

Post by SciBomb97 » February 7th, 2012, 6:57 pm

That must be directly out of a physics textbook XD. I can't understand a word of it.
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Re: Optics B/C

Post by cngu23 » February 7th, 2012, 7:08 pm

SciBomb97 wrote:That must be directly out of a physics textbook XD. I can't understand a word of it.
wolframalpha has some easily understandable versions of the formula, but i can't seem to find them anywhere else
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Re: Optics B/C

Post by foreverphysics » February 7th, 2012, 8:19 pm

cngu23 was correct. I predict Scat would have gotten the right answer. That was not straight out of a physics textbook. I simplified it before typing it down.
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Re: Optics B/C

Post by SciBomb97 » February 7th, 2012, 8:22 pm

Could somebody explain how cngu got 2 diopters?
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Re: Optics B/C

Post by cngu23 » February 8th, 2012, 4:30 am

SciBomb97 wrote:Could somebody explain how cngu got 2 diopters?
The formula for nearsighted correction is -1/max distance in meters= lens power

also, one of the past tests from last year had a few questions about the relation between star temperature and color. Were the rules different last year, because I don't believe that fits under the rules for this year. So should I study it or not?
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Re: Optics B/C

Post by blue cobra » February 11th, 2012, 7:01 am

cngu23 wrote:
SciBomb97 wrote:Could somebody explain how cngu got 2 diopters?
The formula for nearsighted correction is -1/max distance in meters= lens power

also, one of the past tests from last year had a few questions about the relation between star temperature and color. Were the rules different last year, because I don't believe that fits under the rules for this year. So should I study it or not?
The rules were essentially the same last year, but test writers have a tendency to bend the rules a bit (I saw polarization last year, even though that's not in the rules). I think in this case you're supposed to recognize that higher frequencies of light have higher energies, so the hottest stars will be blue.
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Re: Optics B/C

Post by dlu66061 » February 12th, 2012, 3:44 pm

I am new to this forum. This question may have been answered but it is quite difficult to search and pinpoint the answer among 260+ posts.

The rule for LLS says "The mirror faces must initially be covered with a cardboard sleeve or other easily removable non-reflecting, opaque material." What is the purpose here? I have seen a couple of invitational events where no covering was used. Did they NOT do it correctly?

With sleeves where contestants cannot use mirrors as guidance, what kind of assumptions can contestants use for alignments? With the pictures in Mr. Chalker's http://soinc.org/sites/default/files/SO ... 110918.pdf and http://soinc.org/sites/default/files/SO ... 110918.pdf on sonic.com, I find it difficult to find a reference for alignments. With a long distance for the laser to travel, a slight change in angle of any of the mirrors used can throw the results far away from the target.

I hope to get some advices.

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Re: Optics B/C

Post by andrewwski » February 12th, 2012, 4:12 pm

The purpose of the coverings is to ensure the competitors cannot look through the mirrors to align them.

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Re: Optics B/C

Post by chalker » February 12th, 2012, 6:38 pm

dlu66061 wrote:I am new to this forum. This question may have been answered but it is quite difficult to search and pinpoint the answer among 260+ posts.

The rule for LLS says "The mirror faces must initially be covered with a cardboard sleeve or other easily removable non-reflecting, opaque material." What is the purpose here? I have seen a couple of invitational events where no covering was used. Did they NOT do it correctly?

Yes, they did NOT follow the rules if the mirrors were not covered. The reason behind the rules is that without covered mirrors, it is EXTREMELY trivial to align an arbitrary number of mirrors very quickly and get the laser right on the target (essentially via putting your eye right above the laser or target and 'sighting' the opposite).
dlu66061 wrote: With sleeves where contestants cannot use mirrors as guidance, what kind of assumptions can contestants use for alignments? With the pictures in Mr. Chalker's http://soinc.org/sites/default/files/SO ... 110918.pdf and http://soinc.org/sites/default/files/SO ... 110918.pdf on sonic.com, I find it difficult to find a reference for alignments. With a long distance for the laser to travel, a slight change in angle of any of the mirrors used can throw the results far away from the target.

I hope to get some advices.
The mirrors can still be used as guidance with my business card based method. The thickness of the mirrors and business cards are very easy to see and you can make measurements off of either the front surface of the mirror / business card combo, or off of the front surface of the block (which happens to be the back surface of the mirror). In addition, with my design you can easily remove the covering with no chance of messing up the mirror alignment since you can use a finger to push down on the top of the mirror block while sliding the card out.

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