Saturday, October 18, 2008
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27 comments:
I don't want to speak for everyone, but I think that we should have 18 and 21 due on Tuesday and start having homework just due every Tuesday primarily because I want to be able to start grasping these new concepts that we are diving into and also the its not enough time to understand the concepts and do the homework problems in the time frame between Tuesday to Thursday. I mean it was good for the review homework because we had already viewed those concepts.
I would feel sad if we were to restrict ourselves too much with an absolute rule, but I do see the value of having enough time to really think about something thoroughly and understand it. How about if we have a guideline that, unless there is an "emergency", we have a week, or more, between when a problem is assigned and when it is due?
(Sometimes I wonder: do people really use that time? I have this fear, perhaps unfounded, that people might wait until a few days before something is due to start working on it?)
To change the subject slightly, I made up a take-home midterm today that I think is really interesting, but I was afraid to spring it on you too suddenly. When would be a good time, where you would feel ready to start that?
It is mostly deg. pert theory. I was thinking that we should allow a week for that (between when it is posted and when it is due) and that everyone should work on their own, except they can ask questions as comments on this blog. (We can start a midterm post for that when the time comes).
I actually think that starting the midterm this coming week would be most ideal. Only because this first GRE is finished and there are three weeks left until the next.
As for the homework due I'd say all that was due on thursday should be due on tuesday just to keep it simple.
Jesse, to confirm, that would be
#18
#21
#22 ?
If so, I agree that that would be a good amount to be due on Tuesday
Zack, in my opinion, posting the midterm this coming Thursday, and allowing 1 week would be ideal.
(this would leave Tuesday, 10/28 without any hw being due I hope)
I agree with the people above. I think people need a week in between homework so they can manage all the other things they have due also, to keep it all balanced out and not fall behind in any class. I'm excited for the take home midterm! Thursday to Thursday would be ideal so that we could have over the weekend to get a good start on it! 18, 21, 22 due Tuesday sounds good to me! Hope you feel better Zack!
well, that seems like a good idea, but it might not give you enough time for any HW due on Nov 4. I wonder how Tuesday to Tuesday (Oct 28) would be for the midterm? Would that be better or worse than Thurs->Thurs?
tue-tue is fine by me.
I wonder if we can add a poll feature to this blog for such votes? hehe
tuesday - tuesday would work just as well for me.
since we've already covered #22 fairly thouroughly in class what is there left that we should do?
Sorry guys, but I think have to disagree about the homework. I'm all for having less homework, in order to think about the problems more, however I wouldn't say that we have an exorbitant amount of homework in the first place. I felt that last week was really productive, with a good amount of homework due on tuesday and then thursday was a cumulative effort between everyone to really understand the ideas in the homework. So my proposal would be to have homework due tuesday, and that day Zack would pretty much lecture through ideas. Then Thursday have a less homework on similar topics and thursday have a more open discussion, which is what I think Zack wanted in the first place.
As for Homework due this Tuesday, I dont feel that there is much left that we didnt go over on 22. So I guess that leaves 18, 22 and 23, though I dont quite understand 23.
Let me know what you all think.
I like the idea of the takehome midterm. They're a much better learning experience than in-class tests, and they don't restrict the test to only a couple of concepts. Tu-Tu is fine with me.
So I take it we just turn in what was due Tuesday then?
Zack, I hope you feel better. I'm fine with having 18, 21, and 23 due on Tuesday. I think in class we covered all the bases for 22.
and did you mean posting the exam this tues. the 21 and having it due the 28?? oh dear, i have an issue there since my GRE is on monday the 27. Can you not post the exam at all this week but instead post it the 28? i don't see a need to rush this.
Derek for problem 23 he just wants you to calculate the L_z 1x1 matrix for the ground state, the 2x2 matrix for the first excited state and then if you want the 3x3 matrix for the second excited state.
Dear Isotope,
I don't think we can wait that long. In the quarter system if you don't rush, then the quarter is over.
-Zack
Regarding 22, we have pretty much covered that. There is an approach that simplifies it, which is to begin with a change of basis from (n,l,m) to "x,y,z". [that is, to Psi-200,
Psi-2x, Psi-2y, Psi-2z].
Would it be worthwhile to turn in a synopsis (summary) of that problem which emphasizes the matrix, the eigenstates, the corresponding spatial states (with picures) and a mention of the energy order and remaining degeneracies? (about one page, not showing any integrals or eig. vectors calcs,...)?
In not, that's fine, but if that seems worthwhile you coud do that too along with 18 (focuss on that one) and 21 we kind of did in class, but it would fine to redo it yourself and turn it in.
Thanks Zack, i understand. Then i prefer having a thurs.-thurs. exam.
So definitely 18 & 21 for tues., and problems 22(summary) and 23 would be like extra credit?
Hi Blog,
I like the idea of a Tue to Tue (Oct 28) midterm at home!
On #23, it appears that for the 3x3 matrix elements of Lz, the first 2 rows are zero except the last element of row 2. Is anyone getting the same result? or am i just too sleepy and should redo these tomorrow...
I'd also prefer to have the midterm from Tu-Tu. Out of curiosity, how many problems are we looking at for this midterm Zack?
Isotope said: "18 & 21 for tues., and problems 22(summary) and 23 would be like extra credit?"
--That seems fine to me. (Zack)
Bobby: "I'd also prefer to have the midterm from Tu-Tu. Out of curiosity, how many problems are we looking at for this midterm Zack?"
Ok. How about if I post it this evening (about 7 PM) and then it would be due in class the following Tuesday.
I am thinking of 2 or 3 problems. They are not that long or hard, but not too easy i hope. I would guess that the calculations required would take you about 4 to 10 hours. However, a lot of the emphasis will be on deciding which of your results are the most interesting and looking at and discussing those results, and perhaps their relationships, in a thoughtful and cogent manner.
Thus I would suggest trying to finish the calculation part of the problems a few days before it is due, to give you some time to mull over your results.
In fact, if it were me, I would do the calculations right away, if possible...
Hi class,
I have a question on problem 21. I tried to figure out what L_z is in terms of ax+,ax-, ay+ and ay-.
According to lecture it should be L_z=i*hbar[ax-*ay+ - ax+ * ay_]. Is this correct? I always end up with something different...
Best, Tim
Tim:
Yup, that's right. Your mistake might be forgetting the - sign (Lz = xpy - ypx). The quantities xpy and ypx have 4 terms identical terms aside from sign. If you forget the - sign in front of the "ypx" term, then you'll end up canceling the wrong terms.
Hope this helps,
-Jon
AHHH thanks Jon, this helped a lot!
just a minute. I am working on it.
ok, I have a question regarding the basis we are all using for the Harmonic Oscillator.
I have used the notation that the ground state was Psi_0, 1st excited state Psi_1, and so on. But now I'm remembering that Zack might have mentioned that he prefers Psi_1 to be the ground state?
I understand that normally this wouldn't matter very much, but like Zack said, we all need to work in the same basis to compare answers.
-E
Hi Eliot,
my personal guideline is to use the quantum number 'n' (in the energy) everytime in the wavefunction psi_n. I call the ground state the 0th state when this is conform with the energy, e.g. '0' for the ground state of the harmonic oscillator because E_0 != 0 for n=0.
When this is not possible (-> hydrogen atom, inf. square well), I denote the ground state with "1".
Thats my way which seems at least a bit reasonnable.
How is the rest dealing with this problem?
isotope,
For 23 I get that the 3x3 matrix has 4 elements in it with the diagonals and corners zero because we only use one +\- operator and then the rest of the matrix being hermitian. I set the matrix up by rows going like psi20, psi11, then psi02. So only the matrix elements with 11 and 20 or 02 terms should give something, namely a +/- sqrt(2)ihbar.
Hope it helps.
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