8.07 - Electromagnetism II Fall 2017

Lecturer:  Prof. Alan Guth
Recitation Instructor:  Prof. John Belcher
Teaching Assistant:  Cagin Yunus

Announcements:

SUN 11/19/2017: PROBLEM SET 9A IS POSTED
Dear 8.07 Students,
Problem Set 9A is now posted. Problem Set 9B will be posted sometime next week, and they will both be due on Friday, December 1, the first Friday after Thanksgiving.
See you tomorrow,
— Alan Guth —

SAT 11/18/2017: UPCOMING PROBLEM SETS
Dear 8.07 Students,
As the term is approaching its end, there will be only two more problem sets — although one of them will be larger than normal.
I don't think that any of us want a problem set to be due on the Friday after Thanksgiving, so Problem Set 9 will not be due until the following Friday, which is December 1. This will be a longer than normal problem set, since it will represent two weeks of lectures. Problem Set 10 will be due the following Friday, December 8. The last day of classes will be Wednesday, December 13, so there will be two classes after the last problem set. I will post some review problems for the final exam, with solutions, which will include (but will not be limited to) material from the last two lectures. The final exam will be on the first day of final exams, Monday, December 18, in 6-120.
I expect to have Part A of Problem Set 9 ready by tomorrow morning, in case some of you want to start on it this weekend. Part B will be posted sometime during next week.
See you on Monday.
— Alan Guth —

SUN 11/12/2017: QUIZ 2 RESULTS
Dear 8.07 Students,
Your grades for Quiz 2 have now been posted to the Gradebook, along with a calculation of your weighted average to date (which includes Quizzes 1 and 2 and Problem Sets 1-7). I have also posted, on the Exams tab of the website, histograms for both Quizzes 1 and 2 which show estimated letter grade equivalents of the quiz scores.
The material has gotten more difficult since Quiz 1, so the results were not spectacular, like the Quiz 1 results. The class average was 68.8, with a very wide spread---the standard deviation was 22.6.
The wide spread of the grade distribution shows that some of you have mastered this material, but others are very weak. The top grades were excellent: one perfect paper, and grades of 96, 95, 94, 92, 90, and two 89's. According to the letter grade estimates, 32% of the class earned A's on the quiz, and 61% earned A's or B's. That's very good. However, 23% earned D's and F's. For those of you who fall into that category, I urge you to go back over the problem sets and practice problems, and come to office hours and ask questions about the parts that puzzle you. John Belcher, Cagin Yunus, and I will be glad to try to help you.
Problem 3 of the quiz was taken verbatim from the Practice Problems, for which solutions had been posted, yet the average was only 58.5% on that problem. 35% of you did the problem perfectly, but there were many who seemed very confused. I have to admit that I am not sure how this happens. I would appreciate any comments from you about why a problem from the Practice Problems can cause so much trouble. Any comments by you on Piazza (anonymous is fine) would be helpful.
The "weighted average to date" was computed by first computing a problem set average, defined as the total of your scores (including extra credit) expressed as a percentage of the maximum score without extra credit, which was 586. The weighted average was then equal to 0.25 times your problem set average plus 0.75 times your quiz average. (This is the same ratio of homework to quiz/exam scores that will be used in computing the final grades.) The class average of these weighted averages was 82.9%, with a standard deviation of 13.1% --- which I think is very good. But I hope that on the final exam we can reverse the trend that we had in going from Quiz 1 to Quiz 2.
Best wishes,
— Alan Guth —

TUE 11/07/2017: LOCATION OF REVIEW SESSION TONIGHT AT 8:00 PM
Dear 8.07 Students,
The Review Session tonight, by Cagin Yunus, will take place at 8:00 pm in Room 26-328.
Reminders: Cagin will also hold an office hour today from noon to 1 pm, in Room 8-306, and John Belcher will hold office hours today from 3 to 5 pm, in Room 37-695.
Good luck on the quiz tomorrow,
— Alan Guth —

SUN 11/05/2017: FORMULA SHEET FOR QUIZ 2 IS POSTED; INFORMATION ABOUT THE QUIZ
Dear 8.07 Students,
I have just posted the formula sheet for Quiz 2, which will take place in class on Wednesday (Nov 8). It is 11 pages long, and is intended as a general summary of the course so far, as well as being a useful resource of equations. I would recommend that you use it in your studying: if you understand all the equations on the formula sheet, you are in great shape for the quiz.
Since the document is long, I am posting it in both 1-up and 2-up formats. The 2-up format is intended for printing --- it will almost certainly give you larger text and smaller margins than the 2-up option in your printing software. At the quiz we will circulate 2-up copies of the formula sheet. If you prefer to use a 1-up copy during the quiz, you can bring your own copy.
The quiz material will in principle include everything in the course so far, since it is cumulative, but it will focus on the material introduced since Quiz 1. Hence it will focus on Problem Sets 4-6, and through Problem 5 of Problem Set 7; Griffiths Section 3.3 through the end of Chapter 4; Lecture Notes 1, 2, and 3; and material presented in class through last Wednesday, Nov 1.
One of the problems on the quiz will be taken verbatim, or at least almost verbatim, from either the Problem Sets or the Practice Problems. The extra credit problems are included in the set that may appear on the quiz. Even though I did not expect everyone to do the extra credit problems, I would like all of you to read over the solutions so that you understand how to do those problems.
Reminders of scheduling for the quiz week:

Monday (Nov 6): office hour by me, 5:30-7:00 pm, Room 6-322.
Tuesday (Nov 7): office hour by Cagin Yunus, 12-1 pm, Room 8-306.
office hour by John Belcher, 3-5 pm, Room 37-695.
Review Session by Cagin Yunus, 8 pm, room to be announced.
— Alan Guth —

SAT 11/04/2017: PRACTICE PROBLEMS FOR QUIZ 2 ARE POSTED
Dear 8.07 Students,
I have posted 7 practice problems for Quiz 2, and their solutions. Later this afternoon I will post the formula sheet, but first I need to get a haircut. (You wouldn't want a shaggy professor, would you?)
— Alan Guth —

THU 11/02/2017: MODIFICATIONS IN PROBLEM SET 7; PREPARATION FOR QUIZ 2
Dear 8.07 Students,
Since I didn't find time to start talking about magnetic fields in lecture yesterday, Problems 6 and 7 of Problem Set 7 will be held over until the next problem set.
Quiz 2, which will take place next Wednesday, November 8, will include the material through Problems 1-5 of Problem Set 7. The reading for the quiz will therefore include Chapters 1-4 of Griffiths, and Lecture Notes 1-3. Lecture Notes 4 have been posted, but they are for cultural interest only, and the material in these lecture notes will not be included on the quiz.
The quizzes from 2012 and their solutions are available on the OCW website,
https://ocw.mit.edu/courses/physics/8-07-electromagnetism-ii-fall-2012/exams/
The timing of the quizzes was slightly different that year, however, so the questions on those quizzes that would be relevant for our Quiz 2 include Problems 3, 4, and 5 of Quiz 1, and Problem 2 of Quiz 2. As I did with Quiz 1, I will be posting a set of problems from Griffiths, with solutions, that you can also use for review.
To further help you prepare for the quiz, the schedule for office hours next week will be modified. I will move my office hours to Monday (Nov 6) from 5:30 - 7:00 pm. I believe that the CTP is locked at 6:00 pm, so if you are locked out, call me in my office at 617-253-6265, and I will let you in. Cagin Yunus will have his usual office hour from noon to 1 pm on Tuesday, in Room 8-306. John Belcher will cancel his office hours on Thursday, but instead will hold office hours on Tuesday from 3 to 5 pm, in Room 37-695.
In addition, Cagin Yunus will hold a review session for the quiz, at 8:00 pm on Tuesday, in a room that will be announced soon.
— Alan Guth —

MON 10/30/2017: PROBLEM SET 6 SOLUTIONS AND LECTURE NOTES 4 ARE POSTED
Dear 8.07 Students,
I just wanted to let you know that Problem Set 6 Solutions and Lecture Notes 4 are posted.
In the solution to Problem 6, Problem Set 6, there is a section titled "Further Discussion: The Potential for r < R". You should consider this optional reading. If you are doing well in the course I think you will find it interesting, but if you are struggling you can skip it. It will not be needed for Quiz 2 or the Final Exam.
Lecture Notes 4 are also optional reading. They include a proof of what I called the Trace Decomposition Theorem, and also a derivation of the formula for the extraction of the traceless part of an arbitrary symmetric tensor. I am posting them for logical completeness, but this material will also not be needed for Quiz 2 or the Final Exam.
Best wishes,
— Alan Guth —

SAT 10/28/2017: PROBLEM SET 7 IS POSTED
Dear 8.07 Students,
Problem Set 7 is now posted. It will be due next Friday, November 3, at 5:00 pm. It will be the last problem set before Quiz 2, on Wednesday, November 8.
— Alan Guth —

THU 10/26/2017: QUIZ 2 ON NOV 8; RECITATIONS AND OFFICE HOURS TODAY
Dear 8.07 Students,
First, I have announced in lecture that Quiz 2 has been changed from the originally announced date (which was Nov 15). It will take place a week earlier, on Wednesday November 8, so as not to conflict with the 8.05 quiz.
Second, John Belcher is out of town today, so Cagin Yunus will be teaching the recitation sections. I will be able to substitute for John's office hour at 5:00 pm. It will be in my office, 6-322, from 5:00 - 6:00 pm. John normally has an office hour-and-half, but I will only be able to do one hour today.
Best wishes,
— Alan Guth —

SAT 10/21/2017: PROBLEM SET 6 IS POSTED
Dear 8.07 Students,
Problem Set 6 is now posted. It will be due next Friday, October 27, at 5:00 pm. It contains 8 problems, of which 1 1/3 are extra credit.
— Alan Guth —

THU 10/19/2017: LECTURE NOTES 3 AND VIDEO FROM YESTERDAY ARE POSTED
Dear 8.07 Students,
Lecture Notes 3 are now posted on the course website, and the video from yesterday's lecture is also posted.
— Alan Guth —

MON 10/16/2017: PROBLEM SET 5 IS POSTED
Dear 8.07 Students,
Problem Set 5 is now posted. Sorry that it is late, but with three conferences during three consecutive weeks (I didn't plan it that way, honest!), and with my desire to significantly revise my treatment of spherical harmonics and traceless symmetric tensors, I was not able to get it ready faster.
The good news is that it is relatively short --- only four problems. And since it is being posted late, I will (like last week) be very generous with extensions.
The solutions to Problem Set 4 are also posted. There are some students who have not handed it in yet, so those students are on their honor, until they hand in their problem sets, not to look at the solutions or to discuss the problem set with anyone who has.
See you soon in lecture.
— Alan Guth —

FRI 10/13/2017: EXTENSIONS ON PROBLEM SET 4
Dear 8.07 Students,
You will recall that in a recent email, I said:
> I think that you will probably be able to do the problem
> [Problem 3], but I will be generous with extensions if you need
> one.
This afternoon I will be tied up at a small conference that friends have organized to celebrate my 70th birthday,
http://ctpweb.lns.mit.edu/netc/netc.html
There are talks 2:30 - 5:30 in Room 34-101, and then a public lecture by Sean Carroll at 6:00 pm in Room 32-123. The talks are open, so come if you want. Sean Carroll's talk, especially, should be both excellent and accessible.
If you need an extension on the problem set, then please contact John Belcher, jbelcher@mit.edu.
Have a good weekend.
— Alan Guth —

WED 10/11/2017: COMMENT ON PROBLEM SET 4
Dear 8.07 Students,
Problem 3 of Problem Set 4 is about the extraction of the traceless symmetric part from a tensor of the form of a product of components of a single unit vector. In lecture today we came almost to this discussion, but not quite. Tonight I will be able to post Lecture Notes 1, which will include this description.
I was considering holding over Problem 3 until next week, but since the problem set is short in any case, I think it is best to keep it in this week's problem set. I recommend that you read Lecture Notes 1 when they come out, go to recitation class tomorrow and ask any questions, and then work the problem.
I think that you will probably be able to do the problem, but I will be generous with extensions if you need one.
I apologize for not having had Lecture Notes 1 ready to post a few days ago, but I've had conferences for the past two weekends and also next weekend, so life has been very hectic. I expect that my life will be much more manageable starting next week.
Best wishes,
— Alan Guth —

MON 10/09/2017: PROBLEM SET 4 IS POSTED
Dear 8.07 Students,
I posted a rather short (3-problem) Problem Set 4, that will be due this Friday, October 13.
— Alan Guth —

TUE 10/03/2017: REVIEW SESSION TONIGHT AT 8PM IN ROOM 26-328
Dear 8.07 Students,
This afternoon John Belcher will be holding office hours from 3:00 pm to 5:00 pm, in the usual place, Room 37-695.
This evening Cagin Yunus will be running a review session starting at 8:00 pm, in Room 26-328. The format will be open-ended, but it will probably run (my guess) about 2 hours. Of course you should each feel free to come and go at your convenience.
Good luck on the quiz tomorrow.
— Alan Guth —

MON 10/02/2017: PREPARATIONS FOR QUIZ 1, ADDENDUM
Dear Class,
In my last email I forgot to mention something which I said in lecture: one of the problems on the coming quiz will be taken verbatim, or at least almost verbatim, from either the Problem Sets or the Practice Problems. So make sure that you know how to do those problems!
And I'll add a word of advice about studying the problems. It's all too easy to look over the solutions and tell yourself that you understand them, but you want to make sure that you REALLY understand them. So I recommend that you imagine that you are sitting next to the dumbest student who ever existed, and it is your job to explain to the student exactly how each step in the derivations is justified. If you can do that, you will be very well-prepared for the quiz.
Best wishes and good luck,
— Alan Guth —

MON 10/02/2017: PREPARATIONS FOR QUIZ 1
Dear 8.07 Students,
As you know, Quiz 1 will take place in class on Wed, during the usual class period.
To help you prepare for the quiz, office hours have been shifted. Instead of my usual Wed office hours, I will have office hours today, from 4:00 pm to 5:30 pm, in my office, 6-322. Tomorrow Cagin will have his usual office hour from noon to 1 pm, in Room 8-306. John Belcher will cancel his office hours on Thursday, but instead will hold office hours tomorrow (Tuesday) from 3 to 5 pm, in Room 37-695.
In addition, Cagin will run a review session for the quiz, at 8:00 pm tomorrow (Tuesday), in a room that will be announced soon.
I have posted a set of 9 practice problems (from Griffiths) and their solutions on the website, under the "Exams" tab. You will probably not have time to write out solutions to all these problems, but I would recommend that you look at the problems first, try to figure out how you would attack them, and then look at the solutions.
Quiz 1 from 2012, and its solutions, are available on the OCW website,
https://ocw.mit.edu/courses/physics/8-07-electromagnetism-ii-fall-2012/exams/
The timing of the quiz was different that year, so the quiz came after 5 problem sets, while this year it is only 3. Consequently, only Problems 1 and 2 of the 2012 quiz would be appropriate for the quiz on Wednesday, while Problems 3 and 4 involve material that we will be discussing shortly.
Bad news on the videos. Apparently the video people will not be able to salvage the videos from Wed 9/20 or Mon 9/25, and the video from Wed 9/27 was ruined by the absence of sound. We were told from the beginning that these automated videos were experimental. So the videos will resume with the video from today's lecture, and hopefully all the remaining videos will be successful.
Please get back to me if there are any questions.
— Alan Guth —

THU 09/21/2017: OMIT PROBLEM 5 FROM PROBLEM SET 2
Dear 8.07 Students,
Since I didn't get as far as discussing coefficients of mutual capacitance C_ij in lecture --- and since this subject is not actually discussed in the book, either --- Problem 5 of Problem Set 2 is being held over for the next problem set.
If you have already done it and it is attached to your other problems, then I recommend that you xerox it before turning it in, so that you can turn it in next week without much trouble. It will not be graded this week, even if you turn it in. It will be graded as part of next week's problem set.
Sorry for any confusion.
— Alan Guth —

SAT 09/16/2017: PROBLEM SET 2 IS POSTED
Dear 8.07 Students,
For those of you who are ready to start thinking about next week's problem set, it is now posted.
Note that starting this week the problem set is divided into two parts, Part A and Part B, which we would like you to turn in separately, into homework boxes that will be labeled Part A and Part B. Please write your recitation section, R01 (3:00 pm Thurs) or R02 (4:00 pm Thurs) on each part, and place them in the appropriate boxes. This way our two graders can each get started working immediately. Thanks a lot.
Solutions to Problem Set 1 will be posted later this afternoon.
— Alan Guth —

TUE 09/12/2017: 8.07 OFFICE HOURS, STARTING IN 15 MINUTES!
Dear 8.07 Students,
Cagin Yunus will be holding weekly office hours at noon on Tuesdays, starting in 15 minutes from now(!), in room 8-306.
I will be holding weekly office hours on Wednesdays from 4:00 to 5:30 pm, in my office, Room 6-322.
John Belcher will be holding weekly office hours on Thursdays from 5:00 to 6:30 pm, in his office, Room 37-695. John is out of town this week, however, so I will be doing the recitation classes. Cagin will do John's office hours, in Room 8-306.
— Alan Guth —

THURS 09/07/2017: COURSE INFORMATION SHEET IS POSTED
Dear 8.07 Students,
The course information sheet is now posted on the course website,

http://web.mit.edu/8.07/www

You can find it using the General Info tab. There is a PDF and also an HTML web page listing. They are identical, so you can take your pick.
— Alan Guth —

WED 09/06/2017: PROBLEM SET 1 IS POSTED
Dear 8.07 Students,
I just wanted to let you know that Problem Set 1 is now posted on the course website,
http://web.mit.edu/8.07/www/index.html
Click on the "Problem Sets" tab, and you should find it. Let me know if you have any trouble accessing it.
I hope to have a course information sheet in place by tomorrow morning, under the General Info tab.
Best wishes,
— Alan Guth —