Sunday, April 11, 2010

PH253: HW solutions, Exam II

UPDATE 6: Number 9 now also has a solution; multiple bugfixes.

UPDATE 5: Minor bugfixes.

UPDATE 4: Solved through problem 8.

UPDATE 3: Solved through problem 6.

UPDATE 2: Some tedious/difficult problems removed. The first 4 problems now have solutions.

UPDATE: Quite a few more example problems added, and a full solution for the first two. Same link as below. More solutions should follow in the next hour or two.

A few items in advance of exam II:
  • HW 8 and 9 have solutions.
  • A few sample problems, with answers. More will appear tonight; probably very, very late. It is unlikely full solutions will appear in time, but I'll see what I can do. I will at least try to add some hints.
  • An example formula sheet will be posted before the exam, but probably not until Monday afternoon or evening. It takes a long time to prepare. Longer than the exam, in fact.
  • I have not had any email contact since Friday evening ... I hope to catch up on most of my email this evening.


  1. If I kill myself will I have to take the exam?

  2. It will be OK. The practice problems are just that - practice. See what you can do with them. Even if you can't solve all of them, if you at least understand how they should be solved, you will be fine on the exam. Also go through the homework solutions (5-9) and see that you understand those problems. Exam problems will be similar, but largely easier.

    I'd rather scare you a bit into working hard on these problems than lull you in to a false sense of security by posting really easy problems. I am in the process of typing up detailed solutions to some of the problems now, and removing a few that are too tedious or difficult.

    For the exam, remember that you have a choice of problems -- you only need to know how to do about half of them. Don't freak out trying to figure out every last one, pick and choose those that you think you can do.

    I'll put another "update" at the top of this post when I've finished some more solutions.

    Lastly, the exam will be scaled if need be. I'm not out to fail all of you, but the exam needs to be hard enough to see who really knows the material. The average *will* be a C or better, one way or another. Very few of you will fail, possibly none.

    (Also, please be careful what you joke about. It is less funny when you've heard such things spoken in earnest.)

  3. equation 6 should be [....]= .25 d^2
    instead of .25 d^4

  4. Could you post the equation sheet that will be provided for us for Exam 2?

  5. equation 23 should be
    [lambda]= {659.6, 121.5, 102.6} nm
    instead of
    [lambda]= {56.3, 121.5, 102.6} nm

    equation 29 (?) as
    [...]=(h c)/[2 M c^2 lambda]
    instead of [h c lambda]/[2 M c^2]

  6. really tiny comment: eq. 32 missing a G(t) on LHS or eq. 33 has ex. G(t) on RHS

  7. Think it is ok now ... lost a G(t) in equation 32.

  8. :-) We understand you are human too.
    Call it even since you give us lots of partial credit on test two/too.

  9. quick question:
    in soln to 9, for eq. 46, why is n=0 plugged in for ground state when above the problem stated n=1?

  10. Question on problem 9b:
    eq. 46 used n=0 for ground state while above says n=1 is lowest state. Which is right?

  11. Basically a historical accident ... for the hydrogen atom we start out with n=1, but for the harmonic oscillator we always start out with n=0. The n=1 is a typo.

    So, the text should read "for the lowest state, n=0, ..."

  12. I knew it! History never makes sense!

  13. Indeed, physics makes sense, it is the historical baggage that confuses things ;-)

  14. Also, there will be tons of partial credit ... simple errors will not take off much, it is easy to make mistakes. If the concepts are right, but the math has some small mistakes, you'll be OK.