US Physics team

Colleges & Universities A-Z Massachusetts Institute of Technology
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<p>It seems that the tests have been getting easier over the years. I thought the '99 test was much, much harder than 2004, for example. I'm taking the test tomorrow morning. Still have a lot of electromag. to review.</p>

<p>Texas, I know the camp is intended to choose the IPhO team, but you would assume those who did well on the test would be the best prospects for the team, unless of course their is something significantly wrong with them (they cheat, etc.). I did have one question about the camp- is it mostly testing to see who is most qualified, or is there a lot of teaching/learning too? If it's the latter, which texts do they use at the camp?
Thanks again</p>

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<p>
[quote]
you would assume those who did well on the test would be the best prospects for the team,

[/quote]
</p>

<p>well, the stuff they consider other than the test addresses physics "teachability" in a sense. Most physics students are not exposed to physics outside the AP curriculum. But the olympiad definitely covers more topics in more depth than the AP does. The members of the traveling team will need to learn the difference in a fairly independant way. So knowing the math background of the semifinalists is relevant. They may also want to see that the apparent performance on the test is supported by other performance factors like grades and test scores. They also want to pick people who are presentable enough to represent the U.S., so they ask for the recommending teacher to address that (I guess they don't want "smart but embarrassing"). They also have a rule against participants in more than one olympiad. I'm guessing this is out of some sense of fairness, but it is a factor that may mean they don't get the absolutely best people. (it's amazing how much overlap there is at the top on these things).</p>

<p>
[quote]
I did have one question about the camp- is it mostly testing to see who is most qualified, or is there a lot of teaching/learning too? If it's the latter, which texts do they use at the camp?

[/quote]
</p>

<p>the first day or 2 there are lectures on topics outside the AP curriculum (light, heat, optics, guantum mechanics, etc.). No text book, although they give team members a whole box full of books (including the 3 volume Feinman set).The rest of the time is spent taking and going over tests. That is used both as training, and as a basis for selection of the traveling team. There are also some sit down dinners, photo ops with politicians, and social activities. If you behave in a way far outside acceptable conventions, presumably that would also be factored into selection.</p>

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<p>I can see your point about needing to be able to pick up new concepts quickly. I'm not worried about this part of the selection, it's just that I couldn't see the reasoning behind it at first.</p>

<p>The lab portion was the other thing I was thinking of. I've done roughly 35-40 two hour labs over the past two years (from mechanics, e+m, thermo, optics, waves...). I was thinking of including a list of them, because at least from my own experiences high school classes typically have few labs (due to time, equipment, or other reasons), and so having done many labs is atypical. Since the lab is a significant portion of the IPhO I wonder if they would have any interest in this. Still, they don't ask for any additional information and I'm a little hesitant to put a list in, as it may seem out of place.</p>

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<p>Samwise - 35-40 labs! Wow, I'm impressed! I think you want them to know that. How about writing it up and giving it to your teacher to include with his/her rec letter? And good luck. Please let me know if you get a camp invite.</p>

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<p>I made it as well and think i got a better score on the 2nd test than the 1st--really cool problems are more suited to me. </p>

<p>congrats to the other winners. go my school, we had 3 winners.</p>

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<p>I went ahead and typed up a list. Once again, thanks for your help texas. You're an amazing help to all of the students here. I'll be sure to let you know if I get into the camp, though I'm not expecting much.</p>

<p>(On a side note, my rec letter came from a physics teacher, but not the teacher administering the exam. Hopefully they won't mind this.)</p>

<p>I'm off to sleep, tomorrow's the big day :D lol</p>

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<p>I guess we're allowed to discuss the semifinal exam now. How'd all of you guys do?</p>

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<p>eh, not bad I suppose, but not great either.
I kept second guessing myself on the B1 derivation. In fact I chose a really terrible way to do it. And for the potential difference I just took the definite integral, had to think back to "u substitution." haha
Completely botched the thermo problem on part A. I doubt I will get any points on that one, but hopefully I will get most of the points for the rest of part A. Probably not A1c, and the last part of A3.
The trick on A3 was to treat the source and image as a double slit, except that the image is phase shifted an additional pi (because of the reflection). Luckily I done a problem just like that. I didn't know what the time average intensity was though, so I just put the cos^2 function. Doubt they will give me any points for this. </p>

<p>By the way, on 1c, do you just use the voltage that was across the resistor in a (that is now replaced with the capacitor), or do you recalculate the voltage as if that wire was removed (so 1 less resistor) and then use that voltage for the capacitor? Ugh, that was a mouthful.</p>

<p>Hmm, also, does anyone have a solution to B2?</p>

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<p>For A1 with the capacitor, after a while the capacitor will not have any current passing through it. So, treat the capacitor as if nothing exists (no wire).</p>

<p>For B2, I believe the frictional force is proportional to how much of the block is over the frictional surface. Thus, you get a differential equation which turns out to be a sinusoidal function. After the whole block is completely on the surface, there is constant acceleration.</p>

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<p>How was the thermodynamics question to be done? Also, for A3, isn't there a phase shift for reflection only if a wave reflects of a surface with higher refractive index? For some reason, I recall (maybe incorrectly) that in the first part of A3, it was just a vacuum, both above and below the reflective surface.</p>

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<p>hey guys,</p>

<p>I am Canadian. However, these questions seem very intersting. does anyone have a link to past or this year's questions?</p>

<p>please PM it if you cannot post it on the forum</p>

<p>Thanks a bunch guys!</p>

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<p>Michigan, you are right for A1, but I disagree with you on the one with friction. I think you use a function for friction, and your variable is the normal force because not all of the weight is on the frictoinal section, so it is a force function with an X dependance, so you just have to integrate the force dx to get the work, and then you get all the information you need to know.</p>

<p>I really liked the exam...also for A1, i've done aproblem just like that--it becomes easy when you see that A and B are exactly symmetrical so no current flows through the middle one and it just becomes a simple Parallel circuit. Yes once a capacitor becomes charged, it is as the same potential as the battery therefore there is no current (Why would there be?) and so the charge on the capacitor is just CV...</p>

<p>Our class never covered double slit because it seemed kind of boring and pointless but I wish we had now...I hope they don't take me off just for not remembering some formula.</p>

<p>For B1, using some multivariable calculus makes it a really easy problem...I really liked the gauss's law for Gravitation, that was some cool stuff.</p>

<p>I really hope i make it...</p>

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<p>Princetonwannabe: check out the past semi-final exams here:
<a href="http://www.compadre.org/psrc/evals/olympiad.cfm%5B/url%5D"&gt;http://www.compadre.org/psrc/evals/olympiad.cfm&lt;/a&gt;&lt;/p>

<p>I also really liked B2. For the friction one, I asumed that the friction force would increase linearly as more of block passed the friction boundary. For me the thermo one was probably the easiest. For a part of A1 I got stuck with the integral of 1/(x^2 + b^2) dx or something like that. I've only taken AP calc, and since i didn't have my ti89 i just left it as some huge expression. I forget the circuit one, but remember making some assumption about current not going through some branch that I wasn't sure of. That mirror problem really confused me; I have a hard time visualizing light waves.</p>

<p>Any idea when we'll get the results? I highly doubt I'll get invited, but i just want to know how i did.</p>

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<p>lol Spyder, I did the same thing for B2--linear function of distance (friction). </p>

<p>Yah, I'd like to know when we get results too...you're think about the circuits sounds like what my trick was--the middle branch had no current (by symmetry).</p>

<p>So, anyone remmeber from last year when results came out?</p>

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<p>you won't get results in the sense of a score. The top scorers will get invited to training camp, but they won't be told their score. Unfortunately, no one else receives any feed-back at all. I suspect that they do not bother to even grade the papers of people who did not solve enough problems to be in the running for top 24.</p>

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<p>What I meant was, the displacement function was a sinusoidal function of time. You are right that the force is linear in the displacement.</p>

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<p>Anyone (especially texas) have any idea what score might make it to the top 24? I realize that scores are never given out, but anyone have an estimate?</p>

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<p>it's more than just the score on the semi. They also look at your transcript, rec letter, test scores. Ignoring that, the cut-off score for the exam probably varies a lot from year to year because you're dealing with small numbers.</p>

<p>The invitations will actually go below the top 24. Some of the people in the top 24 will turn down their invites because of conflicts with other programs.</p>

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<p>On part B2 a)</p>

<p>the force, I assume, is F= (mu)N = (mu) Mg (x/L) </p>

<p>where x is the distance of the bar over the region with friction</p>

<p>so, W = int (F*dx) = int [ (mu) Mg (x/L) dx ] = (mu)MG/L * int [ x dx] </p>

<p>taking the definate integral from x= 0 to x = L I beleive gives</p>

<p>W= (mu)MGL/2</p>

<p>MG(Hcrit) = (mu)MGL/2
Hcrit=(mu)L/2</p>

<p>hmm, thinking back I think I messed up somewhere after taking the integral, :( I better go ask for my solutions and see. </p>

<p>now, what about the time to come to a stop? this one I can't figure out
I keep getting an (mu)g/L *dt^2=dx/x
taking the RHS integral from 0 to L doesn't work, so... can someone point out what's wrong with my reasoning?</p>

<hr>

<p>On the mirror problem, yes there may be a vacum above and below the mirror, but the reflection is off the actual (glass?) mirror (n~1.5), so I think there is an additional pi phase shift. </p>

<p>stcoleridge- really? I find the double slit, diffraction grating, and single slit stuff really interesting. In any case you should take a look before you get to QM. It would be hard to tell why an electron beam creates a diffraction pattern if you haven't done light interference first.</p>

<p>Spyder2287- use u=x^2 + b^2, then du=2x dx and the integral works out nicely. In any case it's probably better that you left this unsolved rather than doing it with your 89, because I think they say you aren't supposed to use the algebra system or graphing features of the calc. Not sure how strict they are on this though. </p>

<p>On the circuit one I think by connecting points of equal potential I ended up with 3 in parallel conected in series to 2 and that in series with another 3. From what you guys are describing it sounds like I made a mistake. Again, I should probably get my solutions.</p>

<p>Good luck everyone! I think I'm pretty much out of the running unless the cutoff is like 50% :(</p>

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<p>When will they let us know the finalist?</p>