Feedback week 13

exam comments:
The test went well, I thought it was a lot better than last time. When will we know the results of the whole test?

I found that the multiple choice questions were challenging but fair. The wording was not as confusing as the first test. THANKS!

Class is going great, the last test was more fair, but the mult choice was not so good, it lowered my score more than I think is fair.

I thought the test this week was a better mix between multiple choice and short answer. I think this made it easier to finish in the time given.

I actually thought that this test was by far the best of the three. I liked how there were a few more multiple choice questions. I got both of the questions wrong that you said more people got wrong than right, which isn't usually the case. But, I realize if I had read the candle image one much more carefully, I would have gotten the right answer. I thought the essays were a lot better than last test's. I was a little hesitant at answering the balloon ones because they weren't as specific, but I did fine on them because I knew my stuff. I think with the essays, the only thing that I'd change is having two questions each worth two points. Because, if I know the answer to the one that's one point and not to the one that's three points, them I'm kind of S.O.L. And, I didn't feel like there was an easily identifiable reason for why one should be weighted more than the other.

I also thought the test was a good review of the material we've gone over in the past several weeks. While the essays took a while to write, I felt really well prepared to answer them in detail.

Thanks for the feedback on the exams... I'm trying to simultaneously make sure these are a fair meausre of learning and address everyone's intersts... Glad we're converging on a useful approach (just in time for the final!).

What would happen to a nuclear weapon if you hit it with a conventional chemical weapon (say a missile)? In the case of a fission bomb, critical mass would not be reached therefore not making it explode. Right? What about the patriot missiles? If one was to intercept a nuclear warhead, would there be a nuclear explosion dousing everyone below in radiation?

Right... it is possible you could just exactly hit a nuclear weapon so that it did cause a fission reaction, but very unlikely. Most likely you would have this highly radioactive material dispersed into a bunch of smaller pieces (U235 or plutonium is still deadly)... still very damaging, but not nearly as bad as if these were to explode all at once. great question.

There's been one question that's been bugging me about nuclear weapons and the physics behind them: the idea of nuclear force seems contrary to one of the main principles of physics - that like charges repel. With this knowledge how is nuclear force possible?

excellent question. In this course, we've explored 3 fundamantal forces in nature --- they are all 'main principles' but two are more common than the other --- gravitation (like attract actually... where masses attract each other), electro-magnetic forces (like charges repell, opposite charges attract). The third force (the strong-nuclear force as it is called) allows for binding of the nucleus, and only acts at VERY short distances... when you are inside the atom and basically the neutrons or protons are touching.

(1) Perhaps for review sessions in the future, you could go over the oldest material first. Having spent the two most recent days on nuclear weapons made the 20 minute review on Tuesday a little unnecessary. I would have preferred that you began the review session with lasers instead. Just a thought. (2) I really loved how you went over the different test statistics in class. It's always helpful to know where you went wrong and what the rest of the class is up to. (3) And I really do appreciate the writing on homeworks, tests, and papers. (4) Thursday had really good picture and animation. The light and hand demo was really neat! I wanna try it at home now! Keep up the good work!

Glad all is going well... yes, for the final review I'll go forward rather than backwards.. how's that?

I hope that you get a chance to tell us what our grades are before we turn in our papers and before the final, just so we know where we are. Also, I would like to know if you curve or not.

I'll see what I can do before your paper, but certainly before the final. If you ever have any quesitons, please feel free to visit during my office hours. As for "curve" well all classes are curved I suppose. If you're asking if I'll use the standard curve 90-80-70--- no I will likely not... see a discussion of grades in the syllabus.

I know it's been a couple of weeks since we talked a little about the "uncertainty principle" in class but I have a lingering question: is the "uncertainty principle" applicable to atomic objects only or does it include all objects (including everyday objects)? In everyday life a cop can tell my position and speed as I drive down the highway but are those approximations and do they contain a certain amount of "uncertainty"? Thanks!

Indeed the uncertainty principle does apply to all objects...however, it doesn't really make sense to apply it to larger scale (macroscopic) objects because the scale of uncertain is the same for both large and small things. The uncertainty is on the order of plank's constant (h) ~ 10^-34 (yes, lots of 0's before you don't know something: ) So for an object on the scale of 1m it's position is 1m +/- (10^-34) -- nobody talks about that many zeros in a measurement. However, if the object is really really small (or low energy for that matter) it becomes an issue.

This class is run so well that im having a hard time finding any more ideas to improve it...

Say... don't feel like you HAVE to ; )

But here is one: in the lectures I am getting confused a lot. I follow much of the material, but sometimes when there are too many words or equations on a slide my attention slips away. I love the illustrations. there should be even more. TWICE as many slides with HALF as much information on each of them. It also helps when one piece of information is revealed at a time. If I am just given a slide with words from the top to the bottom I have a hard time reading the whole thing while listening to Noah and deciding which information to take in. Maybe just give us a minute to read the slide before you say anything. Overly wordy problems just confuse me more while revealing 1 simple concept at a time lets me learn faster and easier. I would just say always err on the side of teaching things too slow. I would rather learn everything right the first time then miss an important part and be confused for the rest of the week.

I'm with you on this... important ideas --- which I failed on the MRI lecture --- sorry. (though there's a note on this on the web-page). I'll take a moment and let ya'll read then talk... or pace things better hopefully. I'm hoping the lecture on energy / population / exponential growth takes your advice to heart.