## 8.07

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# 8.07 - Electromagnetism II Fall 2014

Lecturer: |
Prof. Alan Guth |

Recitation Instructor: |
Prof. Xiao-Gang Wen |

Teaching Assistant: |
Anton Goloborodko |

## Announcements:

Announcements will be posted here throughout the semester.

**FRI 10/24/2014: Quiz 1 histogram, with estimated letter grades, is posted**

Dear 8.07 Students,

I have just posted a histogram of the grades
for Quiz 1, with estimated letter grade equivalents. It is on
the Exams tab of the class website. As it says on the histogram
page,

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. The final grade cuts will be
adjusted to account for the level of difficulty of all the
quizzes and problem sets. |

We have tried to grade as carefully as we can, but grading errors are still possible. If you have any questions about the grading of your quiz, I encourage you to ask about it. I graded problems 2 and 3, and Anton graded problem 1, so it might be most efficient for you to start by discussing it with the person who graded the problem in question. But you can discuss the grading with any of the course staff. Both Anton Goloborodko and Prof. Wen are authorized to change grades, as well as me, but any of us might refer the question to the original grader, especially in evaluating partial credit. In any case, if you are unsatisfied with the decision of Anton or Prof. Wen, you should always feel free to come to me, and I will be happy to consider your point of view. In the end, I hope to make sure that the grading in this course is fair, and that hopefully you will all agree that it is fair.

The same issues apply to problem set grades. If you have any questions about the grading of your paper(s), going back to the beginning of the term, I encourage you to ask about it. For the homework it would probably be most efficient for you to first talk to Anton, but I am very much available to consider any points of disagreement.

Best wishes,

— Alan Guth —

**FRI 10/24/2014: Fringing fields: correction to Wed 10/22 lecture**

Dear 8.07 Students,

There was an item that I intended to mention in lecture
today, but forgot. This past Wed (10/22/14), I drew on the
blackboard a diagram of a capacitor that was initially filled
with a dielectric slab, but the dielectric was pulled part way
out. Where the dielectic is sticking out of the capacitor
plates, the nearly uniform E-field inside the capacitor changes
smoothly into the very small field outside of the capacitor, and
that leads to a fringing field pattern. I showed that
(qualitatively) correctly in my diagram. At the other end of the
dielectric, however, where the edge of the dielectric slab is
well within the capacitor, the diagram I drew in lecture was not
accurate. I showed fringing fields here, too, but that is not
correct. Since the potential difference between the two
capacitor plates is constant throughout the capacitor, the
electric field need not have any discontinuity at the edge of the
dielectric. As long as the edges of the capacitor are far away,
there is a solution in which the E-field is completely uniform
between the capacitor plates, pointing perpendicular to the
plates (just as inside a vacuum-filled capacitor). This
satisfies div D = 0 and curl E = 0 inside each region, as it
must. At the edge of the dielectric it satisfies the right
boundary conditions: E-parallel is continuous across the
boundary, since E is uniform; and D_perp is continuous, since it
is zero on both sides of the boundary. Thus this configuration
satisfies all the requirements, and therefore is the unique
solution to the problem.

A good diagram of this situation can be found at

http://teacher.pas.rochester.edu/PHY217/LectureNotes/Chapter4/LectureNotesChapter4.html#Heading712

in Figures 4.13 and 4.14.

Sorry for the previous confusion, and I hope
that this email straightens things out.

— Alan Guth —

**WED 10/08/2014: Problem Set 4 Solutions are posted**

Dear 8.07 Students,

The solutions to Problem Set 4 are now posted, on the
Problem Sets tab of the course web page.

— Alan Guth —

**TUES 10/07/2014: Rooms for Review Session and Quiz**

Dear 8.07 Students,

The Review Session for Quiz 1 will take place
at 7:30 pm on Wednesday evening, October 8, in Room 26-310. It
will be run by Anton Goloborodko.

Quiz 1 will take place at 7:30 pm on Thursday
evening, October 9, in the TEAL Room, 26-152. You will have two
hours to do the quiz, although it will be intended as a one-hour
quiz.

Best wishes for the quiz,

— Alan Guth —

**SAT 10/04/2014: Problem Set 3 Solutions are posted**

Dear 8.07 Students,

The solutions to Problem Set 3 are now posted, on the
Problem Sets tab of the course web page.

— Alan Guth —

**THURS 10/02/2014: Lecture Notes 4 are posted**

Dear 8.07 Students,

I just posted a set of lecture notes, Lecture
Notes 4, on the "Traceless Symmetric Tensor Approach to Legendre
Polynomials and Spherical Harmonics". They are based on Lecture
Notes 9 of 2012, but I made a few improvements in the editing.
In particular, the equation that is now Eq. (4.32) has been
corrected.

— Alan Guth —

**SAT 09/20/2014: Lecture Notes 3 posted (addendum to Wed's lecture)**

Dear 8.07 Students,

When I ran out of time in lecture last
Wednesday (9/17/14), there were two topics that I did not have
time to discuss. Since these topics are relevant to Problem Set
2, and are not discussed in Griffiths' textbook, I wrote Lecture
Notes 3 to fill in the gaps. You can access them on the Lecture
Notes tab on the course website.

You will probably find these notes useful in
completing Problem Set 2.

Best wishes,

— Alan Guth —

**MON 09/15/2014: Problem Set 1 Solutions are posted**

Dear 8.07 Students,

The solutions to Problem Set 1 are now posted, on the
Problem Sets tab of the course web page,

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

— Alan Guth —

**SAT 09/13/2014: Problem Set 2 is posted**

Dear 8.07 Students,

Hi from San Francisco.

Problem Set 2 is posted, so you can start whenever you find
the time. Since Friday Sept 19 is a student holiday, the due
date for the problem set is postponed until the following Monday,
Sept 22.

Best wishes,

— Alan Guth —

**WED 09/10/2014: Lecture Notes 1 and 2 are posted**

Dear 8.07 Students,

Hi from Oslo.

I just wanted to let you know that Lecture Notes 1 and 2
have been posted, on the Lecture Notes tab of the course website.
These are notes on "Vector Analysis," and "Rotations in Index
Notation," which you may find useful in doing this week's
homework.

Best wishes,

— Alan Guth —

**THU 09/04/2014: Course Information Sheet is posted**

Dear 8.07 Students,

An information sheet describing 8.07 is now
posted, on the General Info tab. Let me know if you have any
questions that are not answered in this handout.

— Alan Guth —

**WED 09/03/2014: Problem Set 1 is posted**

Dear 8.07 Students,

I just thought that I would let you know that
Problem Set 1 is now posted on the course website. The home page
is at

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

from which you can click on "Problem Sets".

As I mentioned in lecture, it will be due on Friday,
September 12, at 5:00 pm. You should turn in the problem sets at
the Physics Department homework boxes, which are at the
intersection of buildings 8 and 16, on the third floor of bldg. 8
and the 4th floor of bldg. 16.

— Alan Guth —

**TUES 09/02/2014: Welcome to 8.07!!!**

Welcome to 8.07, for fall 2014. This web page
is not set up yet, but the course this fall will strongly
resemble the course I taught two years ago, which is archived on
OCW at

http://ocw.mit.edu/courses/physics/8-07-electromagnetism-ii-fall-2012/

Prof. Xiao-Gang Wen will be teaching the recitations this fall,
and Anton Goloborodko will be the teaching assistant. The
lectures will take place from 11:05 am to 11:55 am on Mondays,
Wednesdays, and Fridays in 6-120. The recitations will take
place on Wednesdays at 4:05 pm and on Thursdays at 3:05 and 4:05
pm. The recitations will all be in 26-310, and will each be 50
minutes long.

I look forward to seeing you.

— Alan Guth —