Physics 125ab
Fall Quarter, 2008 and Winter Quarter, 2009
Course Homepage


The Ph125abc sequence covers quantum mechanics at a level of sophistication beyond the introductory Ph 2/12 sequence.  You will see much material that is familiar to you from these courses; but, in Ph125abc, you will truly learn to attack basic quantum problems from scratch and arrive at full solutions that can be tested by experiment.  We will also explore some of the interesting and unusual implications of quantum mechanics.

It is impossible to emphasize how important the core physics courses Ph106 and Ph125 are: these teach you the basic frameworks and techniques that you must know to do any physics.

Ph125ab will cover the basic techniques and results of quantum mechanics along with a small selection of special topics.

Ph125c will cover additional techniques and applications and will be taught by Prof. Wise.

Quick Links

Vital Information

Location: 107 Downs
Time: MWF 10:00 am - 11:00 am
Prof. Sunil Golwala, 311 Downs, Mail Code 59-33, golwala at
Teaching Assistants:
Denis Bashkirov, denisb at
Kevin Engel, kte at
Marcus Teague, mlteague at
Please contact the TAs directly if you would like to make appointments outside of normal office hours.

Office Hours and Contact Information:

Prof. Golwala:  M 6-8 pm, 107 Downs.

Additional office hours can be arranged by appointment or by popular demand. 

If you need to contact me outside of office hours, please try email first.  I am happy to arrange meetings outside of normal office hours, but I am not always available on the spur of the moment.  Please include "Ph125" in the subject line of your email -- I get a lot of email, and I want to make sure I see your emails quickly.

Su 7-9 pm, location SFL room 2-1.
The TAs will rotate through these office hours.

F 4-5 pm, 107 Downs, usually run by Golwala.

Feedback: I greatly appreciate student feedback; feedback prior to the end-of-term evaluations lets me modify the class to fit your needs.  In person, by email, by campus mail, whatever you like.  If you would like to preserve your anonymity, campus mail will usually work.  I have mailboxes on the 3rd floor of Downs near my office and in 61 W. Bridge.

You will also be able to provide feedback via the new Moodle page being used for this course (details below).  Unfortunately, this feedback is not anonymous, so please use one of the above means if you desire anonymity. 


Lecture Strategy

I will not cover in lecture every bit of material you will be responsible for.  There are some topics that are really better covered by reading than by lecture, and some topics that are simple enough that they are a waste of lecture time.  I can use the leftover time to do more examples.

Problem Set Policies

The best way to learn physics is by doing problems.  In addition to the regular problem sets, I list below some links to other sources of problems, some with solutions -- doing problems is the best way to learn.  All these policies are subject to change when Prof. Wise takes over for Ph125c.
  • Problem sets will be posted on the course Moodle page, linked to the syllabus, usually 1 week before they are due.

  • Due date: Tuesday 4 pm at the box outside my office.  No mercy will be granted on the due date and time.  Remember, we give partial credit, so the last 10 minutes of work will not make much difference.

  • Electronic Submission: Electronic submission of problem sets (email or fax) is only allowed if you obtain prior approval from the instructor.  Electronic submission only creates work for the instructor and TAs because the problem set still needs to be printed out for grading.  Any reasonable justification will be accepted, reasonable meaning that you will be, for some well-defined reason, off-campus and unable to turn in the set physically.

  • Late policy: Problem sets will be accepted up to 1 week late at the due date for the following week's set for 50% credit, and after that not at all.  You may turn in part on-time and part late.  Please note on the problem set if it is being split this way.  You do not need to contact me or the TAs to turn in a problem set late at 50% credit, or to turn in part on-time and part late.

  • Extensions:

    • You may take one full-credit one-week extension per term.  No need to contact us, just write it on your problem set.

    • Otherwise, extensions will be granted for good reasons -- physical or mental health issues, family emergency, etc.  You must contact me or one of the TAs before the homework is due and you must provide some sort of proof (e.g., note from resident head, health center, counseling center, or Barbara Green).  A heavy amount of other coursework is not sufficient reason for an extension (though you may use your free extension in such circumstances -- so save it until you really need it!).

  • Solution sets will be also be posted on the course Moodle page when the homework sets are due (usually late the same night or the following morning).  If you turn in the problem set late, you may not look at the solutions until you have turned in your problem set.

  • Graded problem sets will be available roughly 10 days after they are due, outside my office.  You should keep a copy of your homework sets so you can review them with the solutions promptly after the set is due.
In spite of my best efforts, sometimes I make mistakes in assigning problems; perhaps not providing enough information, or giving a problem that results in an algebra nightmare.  I will post corrections via the Moodle page and will also send broadcast emails to the class.  If you are having trouble with a problem, be sure to check to see if a correction has been posted, and feel free to contact me if you think a problem has errors in it or seems overly difficult.


The course grade will be one-third homework sets, one-third midterm, and one-third final.

Collaboration is permitted on homework sets, but each student's solution must be the result of his or her own understanding of the material.  No manual xeroxing is allowed.  See below for some comments on working in groups.

Use of mathematical software like Mathematica is allowed, but will not be available for exams.  Prof. Mabuchi made a very good point when he taught Ph125: It is absolutely essential that you develop a strong intuition for basic calculations involving linear algebra, differential equations, and the like.  The only way to develop this intuition is by working lots of problems by hand; skipping this phase of your education is a really bad idea.  Be careful how you use such packages.

The midterm and final are not collaborative, though you are welcome to consult your own notes (both in-class and any additional notes you take), Shankar, and my lecture notes (including typo corrections).  You may not use other textbooks, the web,  any other resources, or any software of any kind.

Grade Distributions and Anonymously Listed Grades

Histograms of grades for the problem sets to date can be found here (updated 2009/03/25, through final exam). 

You can check that we have the correct grades recorded for you here (updated 2009/03/25 through final exam).  Grades can still be corrected even after they have been turned in.  Please let me know if you find any errors.

Using Moodle Page

This year we are trying out Moodle, course software used by many institutions.  You can log on to Moodle at

A password for the Ph125a page will be provided in class; you can also obtain it from your classmates, the TAs, or myself.  All course logistics and assignments will be announced via the Moodle page.  You will find a listing of the course syllabus, problem sets, and solutions there.  There is also a weekly homework survey.  It would be very beneficial (to me and you) if you could fill out the survey regularly. Especially important is the ``News Forum'', via which I will make course announcements that I believe you will receive automatically via email once you have logged in to the course page.  This is the first time Moodle is in widespread use at Caltech, and the first time I am using it, so please bear with me as I figure it out.

Practice Problems

Here are some links to problem sets and exams from last year.  You can also find extra problems in some of the texts suggested above, as well as on the web.  I can provide solutions to these sets upon request.

midterm fall term
final fall term
midterm winter term
final winter term

Comment on Working in Groups:

It is in general a good thing to work with other students while reading and doing problem sets.  You get to hear different perspectives on the material and frequently your peers can help you get past obstacles to understanding. 

However, you must use group work carefully.  If you rely on your colleagues too much, or take a very long time to do the homework sets, you will do poorly in the fixed-time, independent exam environment.  Empirically, we observe that students with good exam scores tend to also have done well on homework, but that good homework scores do not predict good exam scores.  Exam scores correlate from exam to exam, even on largely independent material.  For example, scores from 2004-2005 Ph106ab:

Notice, in particular, the midterm-final correlation for Ph106b, which is remarkable because the exams covered totally disjoint material (mechanics vs. E&M) and were written by two different instructors. 

To avoid suffering from this problem, I have two suggestions:
This is not just an arbitrary classroom exercise.  In research, one is always under schedule pressure -- because one only has a fixed number of nights at an observatory, because there are funding deadlines, because there are competing groups doing similar work.  It is critical to learn how to cut through irrelevant or unimportant information and get to results in a timely fashion.