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Date: Thursday, 2 June 2005 8:51am
Subject: 8.01 Final Exam and Solutions are posted
Dear 8.01 Students,
The 8.01 website is now complete, with the posting of the final exam and its solutions (under "Exams").
The Grade Management System will be undergoing some
development work in the next few weeks, so I am told that there
may be occasional "hiccups". If you have trouble accessing your
grades, you should try again a little later, and if the problem
persists you should let me know.
You should also be aware that access to the 8.01 grades on
the Grade Management System will be discontinued in a few weeks.
So, if you want to know the details of your grades, you should
look quickly. If you want to know anything after the Grade
Management System is turned off, you can feel free to contact
me. Keep in mind, however, that the Grade Management System
uses an encrypted protocol, while email from me is unencrypted.
I enjoyed working with you this term, and I got to know many
of you by email and a number of you in person. Have a good
summer, and best wishes for the rest of your years at MIT.
-- Alan Guth --
The Formula Sheet for the Final Exam has been posted.
Information About the Final Exam (posted April 27, 2005).
Histograms for the Pre-Final Grade Distributions have been posted. Cuts used for the interim grades are shown for reference.
Review Problems for Final Exam (Week 13) and their solutions have been posted. They are not to be handed in.
Quiz #12 and its solutions have been posted.
Problem Set #12 Solutions have been posted.
The Quiz #12 Formula Sheet has been posted.
Y&F Chapter 37, Relativity (file size 13 MB) class access only
Problem Set #12 has been posted (and revised 5/2/05).
Date: Tues, 8 Mar 2005 3:09pm
Subject: Clarification of Y&F Prob 7.78 (PS 6 Prob 12)
When I was preparing the solutions to Problem Set 6, I read
Young and Freedman's Problem 7.78 carefully, and decided that it
was not quite worded correctly. In the problem you are told that
a particle moves on the trajectory
x = x_0 cos(omega_0 t) and y = y_0 sin(omega_0 t),
where x_0, y_0, and omega_0 are constants. The problem should
have said that omega_0 is a constant, while x_0 and y_0 are
parameters that describe the trajectory of the particle. It
should have added that the particle is found to be capable of
following this trajectory for any value of x_0 and y_0. In other
words, x_0 and y_0 are constants for any one trajectory, but you
should assume that such trajectories exist for all values of x_0
and y_0.
In case my comment confuses you, I attempted to include some
FAQ's below to answer your questions. (An FAQ is a "frequently
asked question," which perhaps has never been asked by anyone,
but which was thought to be a good question by the person who
wrote the document.)
Best wishes,
-- Alan --
*****************************************************************
FAQ's:
1) Do I need to understand the distinction between these two wordings?
2) What is the difference in meaning between the two wordings?
3) Why does Alan Guth think that the wording in the book was inadequate?
4) In the light of the answer to (1), what is the purpose of this email?
Answers:
1) Do I need to understand the distinction between these two wordings?
No. It is a subtlety of language, while the goal of the course is really to teach the subtleties of the laws of nature. If you have any trouble understanding the language of a quiz in this course, be sure to ask me or whoever is proctoring the quiz.
2) What is the difference in meaning between the two wordings?
A "constant" means a number that has one particular value, even though the value of the constant may not have been specified in the problem. Mathematicians often make this concept clear by sometimes saying that an equation is true "for all x," and in other cases saying "there exists an x such that," followed by the equation. Using that language, I would translate the textbook's wording as:
There exist real numbers x_0, y_0, and omega_0 such that an observed motion of the particle can be described by the equations
x = x_0 cos(omega_0 t)
and
y = y_0 sin(omega_0 t).
The wording that I suggested above would be translated in this language as
There exists a real number omega_0 such that for all real numbers x_0 and y_0, there is a possible motion of the particle described by the equations
x = x_0 cos(omega_0 t)
and
y = y_0 sin(omega_0 t).
3) Why does Alan Guth think that the wording in the book was inadequate?
If you only know about the motion of the particle on a single trajectory, as described above, you of course cannot say anything about what the force on the particle would be if it were put at some other point in the (x,y) plane. For example, there could be walls that exert huge forces on the particle that confine it to the region -2 x_0 < x < 2 x_0, and you would not have any way of knowing this from the one trajectory described in the problem. Such walls would cause U(x,y) to become huge for x < 2 x_0 and x > 2 x_0. Since you are asked to find U(x,y), you need to know what would happen to the particle if it were placed at any point (x,y) in the x-y plane.
4) In the light of the answer to (1), what is the purpose of this email?
If I had noticed this subtlety in wording when I made up the problem set, I would have just given you my own version of the problem, without mentioning the problem in the book and my misgivings about its wording. However, I just noticed the subtlety last night. I don't like to assign badly worded problems, so I decided to correct the wording in this email. I felt that to avoid mystery I should explain what the change in wording is about. For some of you this email may add to your confusion: if so, reread the answer to FAQ #1 and think about it no more.
Date: Wed, 23 Feb 2005 2:13pm
Subject: Special session this evening
Since the problem set this week is rather difficult, and
since there are only two scheduled lecture/recitations this week
to discuss the problems, we worried that you might find it
difficult to get enough help.
To alleviate this problem Walter Lewin has graciously agreed
to do an extra class, from 7:00 pm to 8:00 pm this evening, in
Room 26-328.
If you still need help tomorrow, I will have my office hours
at the usual times, 11:00 - 12:00 and 1:30 - 2:30.
Best wishes,
-- Alan --
Date: Tues, 22 Feb 2005 12:45pm
Subject: Quiz 2 regrades are posted
The regradings of Quiz 2 have now been posted on the web.
42 papers were turned in for a regrade, and of those 30 were
given higher grades, with an average increase of 5.7 points. The
class average on the quiz went up from 69.8 to 72.1. Later this
afternoon I will post a revised detailed histogram, while the
Grade Management System histogram updates itself automatically.
The papers will be returned in the lecture/recitation
classes.
If you meant to turn in your paper for a regrade but were
for some reason unable to do it, I would still be happy to look
at it. At this point I would recommend that you keep the
original, but xerox the cover page and the relevant pages and
give them to me, or leave them under my door. Then I'll get back
to you by email.
Profs. Lewin and Chen can also correct grading errors, so it
depends on what they feel is most appropriate in any given case.
-- Alan --
Date: Thurs, 17 Feb 2005 2:50pm
Subject: New rooms for tutoring; Quiz 3 tomorrow
Tutoring will take place later today, from 3:00 - 5:00 and
resuming from 6:00 - 8:00. Again, if you would like a less
crowded setting, the 6:00 - 8:00 range is a better bet. We are
in new rooms. Kenny MacLean will be tutoring in Room 26-210,
and Ilya Sigalov will be tutoring in Room 26-204.
I am having my regular office hours today, from 11:00 -
12:00 and from 1:30 - 2:30.
The formula sheet for Quiz 3 has been posted, or at least it
is about to be. Remember that Quiz 3 will include one problem
that is at most a slight modification of one of the problems (DO or STUDY) on Problem Set 3, and also one problem that will be a
revised version of one of the problems from Quiz 2. Remember also
that there will be a regrade of Quiz 2, Problem 3, so if you have
not already given your paper to your lecture/recitation
instructor, and you would like it regraded, you should bring it to the quiz tomorrow.
Best wishes for tomorrow's quiz.
-- Alan --
Date: Tue, 15 Feb 2005 9:21am
Subject: A grading glitch on Quiz 2, Problem 3
I have heard a number of questions about the grading of
Problem 3 of Quiz 2. Although I have not seen any of the papers,
we had a long email discussion among the staff last night (22
emails altogether!), and I am convinced that there was some
miscommunication between the graders and me, resulting in grades
that were generally lower, and in some cases much lower, than I
intended. The problem was caused by my statement on the quiz
that points would be taken off for "any irrelevant boxed
equation." My intention was to make sure that you weren't
motivated to box all your equations, but I never made it clear to
the graders how exactly this rule should be implemented.
Since it appears that many papers were graded in a way that
was different from what I intended, I would like to regrade the
quizzes as a group. The easiest thing is for us to regrade
Problem 3 of Quiz 2 on Friday, while we are also grading Quiz 3.
So, if you would like your quiz regraded, you should give it back
to us by Friday morning. Prof. Lewin will be returning the
quizzes to you today. I believe that Prof. Chen has already
returned the quizzes to his sections. You can either give your
quiz back to your lecture/recitation instructor in class (whether
you are in Prof. Lewin's or Prof. Chen's classes), or you can
bring them to the quiz on Friday morning. If you turn your quiz
in for a regrade, you can be sure that the grade will either stay
the same or go up, but it will not go down. We are just trying
to correct for our overly-strict grading of Problem 3.
Sorry for the confusion, but please understand that we at
least try to get things right in the end.
-- Alan -- Date: Mon 14 Feb 2005 7:30 am
Subject: Quiz 2 grades are posted
Your Quiz 2 grades are now posted, so you can find them on
the grade management system. There is also a histogram of the
grades posted under "Exams", which is more detailed than the
histogram that you will find in the grade management system.
The class average was 69.8, with a standard deviation of
14.1. While this is lower than last week, I expected that, and I
am nonetheless pleased with the results of this week's quiz. I
would have preferred it if all of you received grades of 65 or
above, but in any case 51 of you did.
If you got less than 100 (which is the real goal!), it is a
good idea to go over the solutions to make sure that you really
understand how to do these problems. Remember that physics is
very cumulative, so understanding this week's material will be a
BIG help in understanding next week's. To encourage you to
review Quiz 2, I will put one "review problem" on Quiz 3, which
will be a revised version of one of the problems on Quiz 2. By "revised version," I mean that the problem will be sufficiently
similar so that if you really understand the solution to the Quiz
2 problem, the solution to the Quiz 3 problem will be
straightforward.
The tutoring cutoff grade for this week will be 70, meaning that all students who obtained a 70 or above on Quiz 2 will
automatically be given credit for 2 sessions of tutoring this
coming Thursday.
-- Alan --
Date: Sun, 13 Feb 2005 12:12 pm
Subject: Quiz 2 solutions are posted
Quiz 2 Solutions have been posted. I tried to write them in a pretty pedagogical
style, so if you had trouble with any of the problems, you can
probably figure out how they should be done. If you're still
puzzled, ask your instructor, see me at my office hours next
Thursday, or send me an email.
-- Alan --
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