8.07 - Electromagnetism II Fall 2012

Course Administrator: Prof. Alan Guth
Recitation Instructors: Prof. Min Chen

Announcements:

Announcements will be posted here throughout the semester.

TUES 12/18/2012: Formula sheet for the final exam is now posted
The formula sheet for the final exam is now posted on the course website, under Exams. I'm sorry that it is so late, but I am doing my best. As with the quizzes, your copy of the final exam will include a complete copy of this formula sheet. It is also intended as an aid to studying. If you understand the meaning of all the formulas on the formula sheet, you should be in great shape for the final exam.
Best of luck on the final.
— Alan —

SUN 12/16/2012: Prof. Chen's Review on Waves, Potentials, and Radiation is posted
The slides from Prof. Chen's presentation at today's review session, on Waves, Potentials, and Radiation, have been posted on the website as Lecture Notes #17. (From what Prof. Chen tells me, due to a computer crash these are not exactly the slides that he showed today. Instead they are an earlier version of the same talk.)
I still owe you a formula sheet, which I understand is very urgent. However, I am still working on overdue letters of recommendation, which are also very urgent. I hope to have a formula sheet by tomorrow night. In the meantime, you should consider the boxed equations on the lecture slides as the first approximation to a formula sheet for Chapters 9, 10, and 11, but that doesn't help for Chapters 7 and 8.
Best wishes,
— Alan —

FRI 12/14/2012: Information about the Final Exam
As you know, the final exam for this course will take place on Wednesday, December 19, 1:30 - 4:30 pm, at Johnson Track (upstairs).
There will be a review session for the final, led by Prof. Chen and Ahmet Demir, on this Sunday, December 16, from noon to about 2 pm, in Room 4-153.
A set of Review Problems for the Final Exam has just been posted on website, under Exams. It consists of 10 problems, all taken from Griffiths' book, from Chapters 9, 10, and 11. It includes solutions, cut and pasted from the solutions manual. Since the source material comes entirely from Griffiths, I am making it available only on presentation of an MIT certificate. Let me know if you have any problems accessing it.
The final exam will in principle include the whole course, but will emphasize the material since Quiz 2. This means that it will focus on Problem Sets 9 and 10, the Review Problems for the Final Exam, and Chapters 7, 8, 9, 10, and 11. There are some topics that we skipped completely, that will not be mentioned on the final exam: Sec. 6.4.2 (ferromagnetism), Secs 9.3.3 through the end of Chapter 9, Sec. 10.2.2 (Jefimenko's equations), and Sec. 11.2.3 (The Physical Basis of the Radiation Reaction). I recognize that Chapters 9, 10, and 11 were covered rapidly. Details were omitted, and you have had on problem sets only three problems from Chapter 9, and none from Chapters 10 or 11. This material will be covered on the final exam, but the problems based on this material will be fairly straightforward ones. For these chapters you are responsible only for material that was presented in lecture, and which is on the posted lecture slides. The Review Problems for Final Exam are intended to help you study this material, and to give you examples of the kinds of problems that I expect you to be able to solve. (These Review Problems may not seem much more straightforward than usual, but in addition I will promise that the exam problems will require less originality, staying closer than usual to the model of these sample problems.)
The final exam will include one problem that is taken verbatim (or at least almost verbatim) from Problem Sets 9 or 10, or from the Review Problems for the Final Exam.
I would suggest that you focus your studying attention on the Problem Sets and Review Problems, making very sure that you really understand how the problems are solved, and how to justify each step. However, if you want to see more sample problems, you might look at the Final Exams from 2009 and 2010, which are linked to our website via the "Fall 2011 site" tab. After clicking this tab, choose "Presentations", click that it is "okay" to view the last day of classes, and then click "Exam Prep" from the menu at the left. Some of the problems on these tests make explicit use of special relativity, which would not be appropriate for our final exam.
Finally, be sure to fill out the online course evaluations! I really want the feedback. Thanks a lot.
Best of luck on the final exam.
— Alan —

THURS 12/6/2012: Problet Set 10: Problem 6 is now extra credit
Since we didn't get as far in lecture on Wednesday as I had hoped, Problem 6 of Problem Set 10 is no longer part of the assignment. It can, however, be done for 15 points of extra credit.
Although Problems 4 and 5 also involve plane waves, I think that you can do them with only the information we have discussed. Problem 4 depends only on the relation between the energy and the momentum carried by electromagnetic fields. Problem 5 can be done by knowing the form and the meaning of the Maxwell stress tensor, and by knowing that the relevant electromagnetic wave is described by Eq. (9.48). Let me know if you have any problems with this.
See you tomorrow,
— Alan Guth —

TUES 12/4/2012: Quiz 2 Makeup today in Room 32-144
The Quiz 2 Makeup will be given today (Tuesday 12/4/12), from 7:30 to 9:30 pm, in Room 32-144 (the same room as our previous quizzes). If you wish to take it, please come.
— Alan Guth —

SAT 12/1/2012: Outcome of poll on Quiz 2 Makeup
[The following email was sent Saturday, and corrected on Sunday. Please continue to use guth@mit.edu to reach me.]
Sorry that I was slow about this, but I needed a lot of time to get my email organized. When the LNS computer system finally came back after being out for 28 hours due to a power surge, it delivered just under 200 emails to me (including over 20 letter of recommendation requests), in a random order, and some of the attachments were corrupted as well. Now I've restored it all to the original order, which makes it much easier to make sense of them.
As for the poll, it turned out that I was right to suspect that some students felt that they had studied for the Makeup, and they want to be able to take it to show what they have learned. There were 17 responses: 13 chose Option A, and 4 chose Option B. None chose option C or recommended anything different.
So, the optional Quiz 2 Makeup will take place on Tuesday evening, December 4, from 7:30 - 9:30 pm. I will arrange a room and notify you.
The grading policy will be as follows.

If you do not take the makeup, then
   If you do better on Quiz 2 than on the final exam, then
      Each quiz will count 20%, the final will count 35%, and the
      homework 25% (as originally planned).
   I you do better on the final exam than on Quiz 2, then
      Quiz 1 will count 20%, Quiz 2 will count 15%, the final
      will count 40%, and the homework 25%.

If you take the makeup, then
   Your grade will be the highest of the following 3 calculations: 
      1) 0.20*(Quiz 1)+0.20*(original Quiz 2)+0.35*(final)+0.25*(homework)
      2) 0.20*(Quiz 1)
           +0.20*(Minimum((original Quiz 2 + Quiz 2 Makeup)/2, 75%))
           +0.35*(final)+0.25*(homework)
      3) 0.20*(Quiz 1)+0.15*(original Quiz 2)+0.40*(final)+0.25*(homework)
Note that the grading for students who do not take the Makeup can alternatively be described as the larger of calculations (1) and (3) above. This grading policy is identical to what I proposed in my previous email, but it is described slightly differently. If anything seems unclear, just ask.
While the four students who chose option B were in the minority, I certainly sympathize with their situation. With the postponement of the Makeup into next week, for many of you next week becomes incredibly pressured. The only ideal solution would be to invent a time machine and go back and undo the power failure. So far, the possibility of success on that project does not look good. I would, however, strongly urge the people who chose B to consider switching to C --- i.e., not taking the Makeup. With the 40%/15% weighting option, a low score on Quiz 2 will not be much of a detriment to your final grade.
In any case, best wishes for those who are taking the makeup.
— Alan Guth —

FRI 11/30/2012: Query about the Quiz 2 Makeup
In class today we had some discussion about what to do about the cancellation last night of the Quiz 2 Makeup. I did not want to finalize any decision until I had given each of you a chance to tell me in private what you would prefer. In particular, I had the worry that there may be some of you who studied for the makeup and feel that you deserve to be rewarded for that study, as promised.
So, if you don't personally care about the Makeup, you can ignore this email. If you do care, I would like you to email me today, by 8 pm, to tell me what you think.
It was suggested in class that the final exam could somehow be used in a way that incorporates the purpose of the makeup. I said I would think about that, and see if I could come up with a proposal. Since the final is only three hours, and the makeup had been planned for two hours, I don't think it works for the final to contain a subset of problems that are intended as the Quiz 2 Makeup. The best problems for a final exam are problems that incorporate a variety of skills from the term, and I don't want to move too far away from that. So, I would like it to be the final exam as a whole that has the possibility of compensating for a low grade on Quiz 2.
So, let me offer the following proposal: For students who do better on Quiz 2 than on the final exam, there will be no change in policy: each quiz will count 20%, the final will count 35%, and the homework 25%. But for students who do better on the final, the final will count 40% and Quiz 2 will count only 15%.
If the Quiz 2 Makeup is given, which depends on the feedback I get from you, then the proposal becomes a little more complicated. For any student who does not take the Quiz 2 Makeup, the proposal would be as described above. For students who take the Makeup, their grade would be the higher of the grades resulting from the original makeup plan, or the proposal described above (using the original Quiz 2 grade).
I plan to carry out the above proposal, unless I hear objections from you.
In thinking about this proposal, remember that I have said all along (see Problem Set 2) that we will push students above borderlines in selected cases, where students whose grades have improved significantly during the term, and students whose average has been pushed down by single low grade, will be the ones most likely to be boosted. The proposal above is a quantitative version of the policy announced on Problem Set 2. We would still look at individual cases and make further adjustments (upwards only) for cases that seem appropriate.
For those of you who want to tell me your opinions about what we should do about the Quiz 2 Makeup, let me suggest a few options, that you can name by letter. But you should also feel free to suggest anything you want.
Option A: I studied for the Makeup Quiz, and I would like to take it next week, under the original plans.
Option B: Since there are so many things going on next week, I would like to cancel the Makeup Quiz. However, I would feel obligated to take it if it were offered.
Option C: I would like the Makeup Quiz to be cancelled, and if it is offered I would choose not to take it. Instead I would settle for the proposal described above.
As I said, if you have other suggestions, please just make them.
If there are any students who choose A, I think that they are only asking for what they have been promised, and I would want to carry through on that. I would of course keep identities private, but I will let the whole class know whether or not one or more students are taking the Makeup.
Sorry for this complicated mess. (I didn't cause the power failure!)
IMPORTANT: My regular email address, guth@ctp.mit.edu, is not currently working. Somehow the Laboratory for Nuclear Science computer system has not yet recovered from yesterday's power failure. So, please respond to guth@mit.edu.
— Alan Guth —

THURS 11/29/2012: Quiz 2 Makeup postponed
Due to the power failure in Cambridge, it seems that we have no choice but to postpone the Quiz 2 Makeup until next week. I'll get back to you tomorrow to let you know when and where it will take place.
If any of you want to reach me soon, use guth@mit.edu instead of guth@ctp.mit.edu, as the latter email system has been squelched by the power failure.
Enjoy the dark!
— Alan Guth —

THURS 11/29/2012: Logistics for Quiz 2 Makeup
Just a reminder that Quiz 2 Makeup will take place today, Thursday, November 29, from 7:30 to 9:30 pm, in the same place as the other quizzes, Room 32-144. The coverage of the quiz will be exactly the same as Quiz 2. If you have a conflict, you should contact me, and we'll try to arrange for you to take the quiz on Friday.
On Friday (November 30), there will be lecture as usual, and I will also have an office hour at the usual time, 4:00 pm.
— Alan Guth —
P.S. The ground rules for the quiz were described in an email sent 11/20/12:

  All students whose grade was less than 75% are invited take the quiz. If your grade on the Makeup is less than your original grade, you keep your original grade. If your grade on the Makeup is higher, then your Quiz 2 grade will be replaced by the average of the two grades, capped at a maximum of 75%. The test itself will be similar to the original Quiz 2, but just a little shorter. The original Quiz 2 was effectively 4 problems (3 + 2 short ones), and the makeup will probably be the equivalent of 3 problems. It will also include one problem that is taken verbatim (or at least almost verbatim) from the problem sets. The goal of the Makeup is to give you motivation to study this material some more, and to give you an opportunity to raise your grades.


SAT 11/24/2012: Problem Set 9 is Posted
Problem Set 9 is now posted.
The good news is that it is not due until Monday, December 3. I decided that it would be moderately insane to have the problem set due the day after the Makeup Quiz.
The bad news is that we cannot postpone Problem Set 10, since the term is ending, so it will be due the following Friday, December 7.
— Alan Guth —

WED 11/21/2012: Quiz 2 and Solutions Are Posted
Sorry for the delay, but Quiz 2 and its solutions are now posted. Problem Set 9 will be posted soon.
— Alan Guth —

TUES 11/20/2012: Quiz 2 Results, Total Grades, Quiz 2 Makeup
The Quiz 2 results are now posted on the Stellar website, and the histogram of grades with estimated grade cuts is posted on the web.mit.edu 8.07 website, under Exams. The solutions are not yet ready, but will be soon.
As I told you in class yestereday, the results of Quiz 2 were very disappointing. The class average was only 55.2, compared to a class average of 73.9 on Quiz 1. The standard deviation was 23.6, which is unusually large. The histogram shows a very wide range of grades, from 9 to 100. On Problem 1, which was taken from Problem Set 8, the average score was only 61%.
To give you a better idea of how things stand as of now, I have computed interim total grades for each of you, which are posted on the Stellar website. There is a histogram of these grades, with estimated grade cuts, on the web.mit.edu 8.07 website, under Exams. The interim grade was calculated as 0.75 times the quiz average plus 0.25 times the problem set average. The problem set average is 100 times the total number of points earned, including extra credit, divided by the total points possible, not counting extra credit.
Since the grades on Quiz 2 seemed too low to ignore, we will be offering an optional Quiz 2 Makeup, on Thursday evening, November 29, 7:30 - 9:30 pm. All students whose grade was less than 75% are invited take the quiz. If your grade on the Makeup is less than your original grade, you keep your original grade. If your grade on the Makeup is higher, then your Quiz 2 grade will be replaced by the average of the two grades, capped at a maximum of 75%. The test itself will be similar to the original Quiz 2, but just a little shorter. The original Quiz 2 was effectively 4 problems (3 + 2 short ones), and the makeup will probably be the equivalent of 3 problems. It will also include one problem that is taken verbatim (or at least almost verbatim) from the problem sets. The goal of the Makeup is to give you motivation to study this material some more, and to give you an opportunity to raise your grades.
Unlike the regular quizzes, the Makeup Quiz will not cause lecture to be cancelled the following day.
In studying, I would recommend that you make real sure that you understand the homework problems. I often tell students that they should imagine that they are sitting next to the dumbest student in the world, and that it is your job to patiently explain exactly why each step is done the way it is.
And you should also come to class, and take full advantage of the staff office hours. I remind you that Ahmet Demir has office hours 4-5 pm on Tuesdays and Wednesdays, in Room 8-316; Prof. Chen has office hours from 6-7 pm on Thursdays, in his office, 24-033D, and I have office hours on Fridays at 4 pm, in Room 8-308.
— Alan Guth —

FRI 11/16/2012: No class or office hours today; Problem Set 9
As we did with the last quiz, we will not have a lecture today, the day after the quiz. I will also not be holding office hours today, as I will be grading the quiz (with Ahmet and Prof. Chen).
Problem Set 9 will appear this weekend. It will not be due until Friday, November 30, due to the Thanksgiving break.
Best wishes,
— Alan Guth —

THURS 11/15/2012: Reminder about Quiz 2 Time and Place
I just thought that it might help to remind you that Quiz 2 will take place tonight, Thurs November 15, at 7:30 pm - 9:30 pm, in Room 32-144 (the same room as Quiz 1).
Good luck!
— Alan Guth —

TUES 11/13/2012: Review session this evening
There will be a review session for Quiz 2, tonight at 7:00 pm, led by Ahmet Demir.
Unfortunately, I failed to arrange a room! Sorry about that. So we are going to start with the hope that the room used last time, 26-310, will be available tonight. If it turns out not to be, Ahmet will look for a nearby room and put a sign on 26-310 to let you know where to go.
I trust that the review session will go well, and I will see you in lecture tomorrow.
— Alan Guth —

MON 11/12/2012: Formula Sheet and Practice Problems are posted
I have finally finished the formula sheet(s), now up to 10 pages. They are posted on the 8.07 website under "Exams". I have also posted a set of practice problems and solutions from Fall 2003, when Prof. Bertschinger was in charge of the course.
For the practice problems, I might mention that I consider the wording of Problem 5 to be ambiguous. Where it says "Charges are flowing in the e_y direction," I would say "Charged particles are moving in the e_y direction."
The formula sheet is intended as a summary or checklist of what you are expected to have learned. So, I recommend that you look it over carefully and brush up on any topics that don't seem clear to you.
Best wishes,
— Alan Guth —

MON 11/12/2012: Information concerning Quiz 2
As you probably know, Quiz 2 will take place this coming Thursday, November 15, 7:30 - 9:30 pm, in Room 32-144, the same place as last time.
There will be a review session for the quiz, led by Ahmet Demir, tomorrow (Tuesday) evening at 7:00 pm. The room is not yet known, but I expect to email you and post it on the website tomorrow morning. I also want to let you know that the solutions to Problem Set 8 were posted this morning.
The quiz will in principle be cumulative, as the subject matter is, but it will emphasize the material since the last quiz. That means it will focus on Problem Sets 6, 7, and 8, and correspondingly Chapters 4, 5, and 6. We are skipping the polarizability tensor mentioned on pp. 162-163, and in Chapter 6 we have not yet talked about Sec. 6.4.2, Ferromagnetism.
This time I will be putting one problem on the quiz that will be taken verbatim (or at least almost verbatim) from Problem Sets 6, 7, or 8. This will encourage you to study the problem sets carefully, which I think is a good idea; the other problems will test your creativity.
I am still working on the formula sheet, which should be out later today. I have also located a quiz from a prior year that makes a good practice quiz for us, but I am still trying to contact the instructor to get permission to post it.
Good luck on the quiz. I will see you on Wednesday.
— Alan Guth —

TUES 11/6/2012: Problem Set 7 Solutions; Comment on Problem 5, Problem Set 8
First, I want to point out that the Problem Set 7 Solutions have now been posted.
Second, I have a comment about Problem 5, Problem Set 8. The problem has 4 parts, which are all related. The best order in which to do them depends on the method you choose to use, so you should not feel obligated to answer them in the order given. (As far as this course is concerned, you should never feel obligated to answer questions in the order in which they are given.) In this case, I would probably do part (c) first, but there are different ways to attack the problem.
— Alan Guth —

SUN 11/4/2012: Problem Set 8 posted
I just wanted to let you know that Problem Set 8 is now posted. It will be due next Friday at 6:00 pm, as usual.
— Alan Guth —

FRI 11/2/2012: On Problem Set 7 due today, skip Problem 6
I announced this in class on Wednesday, but I forgot to also put it into an email. If you have already done Problem 6, there is no harm in submitting it with Problem Set 7, but it will not be graded. Please save a copy that you can turn in next week with Problem Set 8.
Have a good weekend.
— Alan Guth —

TUES 10/30/2012: Revised version of Problem Set 7
I have just posted a revised version of Problem Set 7, fixing two misprints, both in Problem 7. In Eq. (7.8), in the second term of the second line, the argument of phi should be the zero vector, and not the r-vector. Also, after Eq. (7.11), the equation d^3x = r^2 dr sin theta d theta d phi was mistyped.
See you tomorrow,
— Alan Guth —

MON 10/29/2012: Problem Set 6 Solutions and Class Contact List posted
I wanted to let you know that Problem Set 6 Solutions have been posted, in case you want some reading during our hurricane day off. I really do recommend that you read the solutions, by the way, even if you already know how to do the problems. We've put a lot of work into trying to make them clear and useful. I should warn you that the posting is perhaps premature --- for some reason my staff has been slow in getting back to me to confirm that they like the solutions. But I wanted you to have access to them today. There is even a chance that when I discuss the grading with the grader, we might change the spot-grading choices. I'll of course let you know if that happens.
I also wanted to let you know that the class contact list is posted, and students in the class should be able to access it with their MIT certificates. I would urge all of you to put yourselves onto the list --- why hide from your classmates? For your convenience, I'll paste below a copy of the contact list questionnaire.
And enjoy our unexpected break!
— Alan Guth —
*****************************************************************
QUESTIONNAIRE:
Name:
Email:
Phone (leave blank if you never answer it):
Living Group:
Comments:
Do you have any objections to my posting your photo with the class contact list? Yes or No?
(If you give me your permission, I believe that I have photos of all of you from the registrar. If you would prefer that I post a different photo, or if you are not officially registered, then feel free to attach a photo to your email.
*****************************************************************

SAT 10/27/2012: Problem Set 7 posted
I just wanted to let you know that Problem Set 7 is now posted. It will be due next Friday at 6:00 pm, as usual.
— Alan Guth —

THURS 10/25/2012: Class contact list
As I mentioned in class a few weeks ago, I would like to set up a class contact list. (Sorry for the delay, but I have been a bit overwhelmed this term.) I think that classes are more fun and productive when students know each other and work together. To make it easier for this to happen, I have found it useful to set up a class contact list on the web. The goal is simply to make it easier for you to find each other. This could lead to regular meetings to work on homework in groups, or maybe just to occasional conversations. Don't feel that you have to be interested in a homework group to sign up. If you want other students to know who you are, that's reason enough. If you are interested, please enter the information that you would like posted on the form below, and email it back to me. The web page will be visible only to other students in the class. Participation is completely voluntary, so you can skip this if you want, but I would encourage you to put yourself on the contact list.
There is a place for comments, which may seem a bit vague. You can put whatever you want, including nothing at all. You might indicate whether you are looking for a study group, or just looking for occasional contact when the problems are difficult. You might be inspired by some samples from the past:

  "I start psets early, available most evenings from 4pm, also 1 to 2:30pm on T,Th. Like ice cream."
  "I'd like to start problem sets at least a little early. I live in Boston, but I have a car."
  "Usually like to do pset for 8.07 on wed or thurs."
I might add that if you send something and then don't like the way it looks, you should feel free to send me corrections, or ask me to take it down altogether. I will act on your requests as quickly as I can.
Best wishes,
— Alan Guth — *****************************************************************
QUESTIONNAIRE:
Name:
Email:
Phone (leave blank if you never answer it):
Living Group:
Comments:
Do you have any objections to my posting your photo with the class contact list? Yes or No?
(If you give me your permission, I believe that I have photos of all of you from the registrar. If you would prefer that I post a different photo, or if you are not officially registered, then feel free to attach a photo to your email.
*****************************************************************

THURS 10/25/2012: 8.07: Grade histogram for Quiz 1; grading errors grading policy
Last evening I posted a histogram of the Quiz 1 results, so that you can see where you stand. On the histogram I marked an estimated letter grade scale. As it says in the PDF file, "The grade cuts shown represent my estimate of what you have earned on this quiz, but they will not necessarily be the numerical cuts that will be used to evaluate your final grade." I don't grade with any fixed distribution of A's, B's, etc., since I want to allow for the possibility that everyone deserves an A. So I have to rely on my own estimates, with advice from Prof. Chen and Ahmet Demir, about how hard the quiz actually was.
We have tried to grade carefully, consistently, and fairly, but I will always admit that there are possible errors. So if you feel that your paper was misgraded, we will be happy to reconsider and try to straighten it out. Prof. Chen graded problems 1(c) and 2, Ahmet Demir graded problems 1(a), 1(b), and 3, and I graded problem 4. If you are not sure about why points were taken off on your quiz, feel free to ask me, or Prof. Chen or Ahmet. Prof. Chen, Ahmet, and I all have the authority to raise your grade for any of the problems if we think it is justified. If it is a matter of deciding how much partial credit an answer is worth, we will very likely refer you to the original grader, since consistency is an important issue for such questions. If you speak to Prof. Chen or Ahmet and are still not satisfied that your grade is fair, you should not hesitate to talk to me. I am ultimately responsible for grading in 8.07, and I want to make sure your grades have been fairly assigned, and that you agree that they have been fairly assigned.
What I said above about grading applies also to the grading of problem sets. I should have said this earlier, but if you feel that there may have been grading errors on any of your problem sets, you can talk to Prof. Chen, Ahmet, or me. And if you are not satisfied with the outcome of any such conversation, please bring it up with me.
For those of you on the left side of the histogram, work harder but do not give up hope. This quiz counts 20% of your grade, with homework counting 25%, with 20% for the second quiz and 35% for the final exam. So there is plenty of opportunity to bring up your grade. Furthermore, I don't grade strictly by the averages. No student will get a grade lower than the numerical average implies, but, as I described in the Problem Set 2 Solutions, at the end of the term Prof. Chen, Ahmet, and I will look at each student's grades individually, and we might decide to give a higher grade to some students who are slightly below a borderline. Students whose grades have improved significantly during the term, and students whose average has been pushed down by single low grade, will be the ones most likely to be boosted. So, if you did badly on Quiz 1 but plan to do better for the rest of the course, you will be a prime candidate to have your grade boosted if it is close to a borderline.
Finally, for those who did badly on the quiz, I have a few platitudes, that maybe are worthwhile. The problem sets are a good tool for making sure that you really understand things. Work hard on the problem sets before you hand them in, and when the solutions come out, go over them carefully. We have put a lot of work into making these solutions useful, even if you have already found the right answer. Make sure that you understand not only what procedure is used to solve each problem, but also how one justifies that procedure. I often urge students to go over problems while imagining that you are sitting next to the dumbest student in the world, and that it's your job to explain to this student exactly why each step is done the way it's done. And of course, if you have trouble figuring out these things yourself, take advantage of office hours! Ahmet Demir has office hours on Tuesdays and Wednesdays, 4:00-5:00 pm, in Room 8-316. Prof. Chen holds office hours from 6:00-7:00 pm on Thursdays in his office, Room 24-033D. My office hours are on Friday 4:00-5:00 pm, in Room 8-308. And if you can work with somebody else in the class, or a small group, that can be a big help.
Best wishes,
— Alan Guth —

WED 10/24/2012: Revised version of Problem Set 6
I have just posted a revised version of Problem Set 6, fixing two misprints. In Problem 1, I inserted a preposition ``to,'' which was missing in the original October 21, 2012 version. In Problem 6, the phrase ``with side larger than $2a$'' was replaced by ``with side larger than $2R$.''
Sorry for any confusion.
— Alan Guth —

THURS 10/18/2012: Quiz 1 and Solutions are posted
Quiz 1 and the Quiz 1 Solutions are now posted in the Exams tab of the website. Your grades should get posted to Stellar tomorrow evening some time, and you will get your papers back at the recitation sections this week.
— Alan Guth —

SUN 10/21/2012: Problem Set 6 is posted
I just wanted to let you know that Problem Set 6 is posted, and will be due this Friday at 6:00 pm.
I hope to have solutions to the quiz posted later today, and solutions by tomorrow.
— Alan Guth —

THURS 10/18/2012: Formula Sheet is posted
The formula sheet for the quiz is now posted. A copy of the formula sheet will be printed as part of the quiz. I know that there is not much time left, but I tried to make the formula sheet pretty thorough, so that you could use it as a checklist of topics that you should understand. So, if possible, try to go over the formula sheet before the quiz.
Best of luck for the quiz.
— Alan Guth —

WED 10/17/2012: Final Lecture Notes 9 finally posted
Finished the final version of Lecture Notes 9, "Traceless Symmetric Tensor Approach to Legendre Polynomials and Spherical Harmonics," and they are posted on the Lecture Notes tab of the website.
Formula sheet coming.
— Alan Guth —

TUES 10/16/2012: Test from 2001 is posted; Review Session reminder
This morning I posted the first 8.07 test from 2001 (when the class was taught by Barton Zwiebach) with the solutions, on our website under "Exams". The test had four questions, three of which (#1, #2, and #4) are relevant to our upcoming quiz. The fourth is about magnetic fields. The 2001 test was given at the end of October, so it is natural that it includes a little more material.
I also want to remind you about tonight's review session with Ahmet Demir, from 7pm until about 9pm, in Room 26-310.
I'm still working on the extension of the notes on traceless symmetric tensors, and then I will also put together a formula sheet.
See you tomorrow,
— Alan Guth —

MON 10/15/2012: New postings and review session
Tonight I posted the Problem Set 5 Solutions, and also a preliminary set of lecture notes (Lecture Notes #9) on the "Traceless Symmetric Tensor Approach to Legendre Polynomials and Spherical Harmonics." I intend to enlarge these notes, hopefully by Tuesday morning, but maybe not until Wed. I will also be posting a formula sheet for the exam.
Sample quizzes are hard to come by, especially since in recent years Prof. Belcher has been lecturing this course with a rather different ordering of the material. I did, however, find a test from 2001, when Prof. Zwiebach was teaching the course, which I will post later today under Exams. The test has 4 questions, one of which is on magnetic fields, which you should ignore. But there are three problems on electrostatics which look interesting. I will post the solutions as well, but I recommend that you try the problems before looking at the solutions.
On Tuesday evening Ahmet Demir will hold a review session for the quiz, from 7 pm until about 9 pm, in Room 26-310.
Quiz 1 will be on Thursday evening, from 7:30 - 9:30 pm, in Room 32-144.
See you later.
— Alan Guth —

THURS 10/11/2012: Recommended: session tonight on Higgs Boson
I just wanted to make a recommendation that you might be interested in the session tonight, at 8:00 pm in 26-100, about "The Discovery of the Higgs Boson: The Final Missing Piece?".
The speakers are Professors Edward Farhi, Jesse Thaler, Christoph Paus, and Markus Klute, and the description is as follows:

  What is this "Higgs Boson?" What does it mean? Come and find out about this elusive particle and what its apparent confirmation means to science and future research. Postulated in the 60s and included in the Standard Model of particle physics, the Higgs Boson particle remained the last unknown in the set of predicted particles that includes quarks and leptons. Learn about the 40-year search from those in the forefront of the discovery and understand the implications of this breakthrough.
My guess is that it will be a fascinating discussion.
— Alan Guth —

THURS 10/11/2012: Problem Set 4 Solutions and Lecture Notes 8 are posted
I just want to let you know that Problem Set 4 Solutions are now posted on the website, and I also posted Lecture Notes 8. These are a write-up of the part of the lecture that I did not get to yesterday, about the traceless symmetric tensor expansion and how to relate the terms to the standard spherical harmonics.
— Alan Guth —

THURS 10/11/2012: Typo and clarification for Problem Set 5
Yu-An Chen pointed out to me that I misprinted the factor that appears on the right-hand side of Eq. (4.12) on Problem Set 5, in Problem 4(c). The correct factor is the inverse of the one that originally appeared. I have posted a revised version. Thanks, Yu-An!
I was planning to send a message in any case, to indicate some flexibility in the answers to Problem 4. I would like you to learn how to use traceless symmetric tensors to describe angular functions. If you are starting from scratch, I think that this is the easiest approach. If you already know spherical harmonics, I think that you will find that the traceless symmetric tensor approach is a useful addition to your body of available techniques. However, I generally hate the idea of insisting that anyone use some particular method for solving problems. So, in Problem 4, where you are asked to use the traceless symmetric tensor method to find Y_{31}, Y_{ll}, and P_4, I will ask the grader to accept any valid answer, whether it uses the traceless symmetric tensor method or not. Of course looking up the answer in a book is not sufficient for credit, nor is it sufficient to name a method and then write the answer --- you have to show the calculation in full. But it is okay to start with any general formula for the spherical harmonics and/or the Legendre polynomials, and then to calculate the special cases that are requested. I still recommend that you use the traceless symmetric tensor method, but I'll accept the principle that it is a free country.
— Alan Guth —

WED 10/10/2012: Update on office hours, review session, and the quiz
I want to make sure that everyone knows that we will have our first quiz on Thursday, October 18, a week from tomorrow, from 7:30 to 9:30 pm, in Room 32-144 in the Stata Center. There will be no class on Friday, October 19.
Ahmet Demir will be holding a review session on Tuesday evening, October 16, from 7:00 pm to approximately 9:00 pm, in a room that is still to be found.
As a reminder, Ahmet Demir has office hours on Tuesdays and Wednesdays, 4:00-5:00 pm, in Room 8-316. Prof. Chen holds office hours from 6:00-7:00 pm on Thursdays in his office, Room 24-033D. My office hours are on Friday 4:00-5:00 pm, in Room 8-308.
— Alan Guth —