Announcements

. Announcements

Announcements

The Best of the Best

While all the students in Fields and Waves I are clearly the best, it is still possible to identify the top performer on each of the assignments and quizzes. The following students either had the top grade on a quiz, showed the most improvement from quiz-to-quiz or were judged to have turned in the best (and usually neatest) of the homework assignments. In no particular order (to maintain anonimity on our posted grade lists) they are: Ann Snider(2), Joohee Kim, Ken Ngai, Ravi Patel, Pierre Dufilie(2), Elizabeth Zinsser(2), Kristin Offt(2), Ryan Connell, Peter Haley, Chris Wolff, Luis Sanchez, Robert Heikaus, Adam Poulos, and Hanina Abduhl Rahim. More names will be listed as more assignments are completed. Each person who makes the list automatically earns some extra credit points.

Comments on Lessons

A summary of each of the in-class lesson topics is being prepared this semester. Reviewing this summary is particularly useful when preparing for quizzes. This document will be evolving throughout the semester, so you should check here for the latest version on a regular basis. Neither the topic list nor the format of this document have been finalized.

Class Schedule

The class schedule has now been finalized. Please note the quiz dates and other significant dates. The quiz dates have been chosen to avoid conflicts with Signals and Systems and DTS, the only other ECSE core courses with Wednesday night quizzes.

Extra Credit

From time-to-time, I will recommend certain seminars that should be of interest to you and also are understandable. (Most seminars at universities are intended for grad students and faculty and, thus, are difficult for undergrads to follow.) If you attend the seminars I recommend, you will earn extra credit points if you email me a few comments on the presentation. For students who cannot attend these seminars due to their class schedules, there will be other opportunities for extra credit. Check the Seminars webpage for info on the first seminar, which will be presented at 3:30pm on 17 February in CII 4050. The topic of this talk, the development of disk drives, involves many aspects of electrical, mechanical and materials engineering. The second talk is on Monday, 3 April at 4 pm in DCC 308. Jillian Banfield, a 1999 MacArthur Foundation Fellow will speak. It is rare to get to meet one of the very, very bright people who has been given the Foundations young genius awards.

Office Hours/Open Shop

Prof. Connor's open shop/office hours are Monday and Wednesday from 10-12 in the studio classroom. Regular class time on quiz days and on days when homework is due (or the day before for the 4 and 6 pm sections) are also open shop.

Comments on Projects

Project 2: There seems to be some confusion about what needs to be signed off on page 5 of the project instructions. At the top of the page, you will find a section called "Testing Your Model." Everyone needs to get this signed, regardless the option you choose below that. This is the signoff for your analysis. You need to write down all the channels (and their frequencies) that your choice of length will block. Show it to a TA or instructor and we will sign it if your numbers look reasonable. If, for some reason, you did not understand that you had to do this, you can get this signed off during class on Monday, since it should not take any real time.

Project 1 is graded and I have put together some comments on the speeds achieved and the reports I received. I was also able to take a few pictures of a representative set of Beakman's motors built during project 1.

Project 1 (Beakman's Motor): I don't know why I typed the word parallel in the first paragraph in the design section. Clearly, the coil should be modeled with a series combination of an inductor and a resistor. The circuit for the motor should include the coil inductance, the coil resistance, a switch (for the communtator), two voltage sources (the battery and the back-emf from the motion of the coil in the magnetic field, the paper clip resistance, contact resistance, and resistances for anything else (air drag, friction at the sliding contact between the coil and the paper clips ...)

Comments on Homework Assignments

Comments on Homework #8

Many students missed 100kHz. There was a lot of confusion about what frequency is low. Remember that in engineering applications, terms like low or high should have a clear definition. In this case, a low frequency is one for which tan(beta d) is approximately equal to (beta d).
Everyone got this one.
Many students missed 100Mhz, probably for the same reason as in problem 1.
OK
OK
For the magnitude of the pulse, some students used 2Vo for the first and Vo for the second when each of those answers is two times too big.
OK
A lot of students do not know how to compute R.
Some students only picked one choice for each question.
OK

Part Two: A lot of students did not know that the reflected power is just gamma squared times the incident power.

Part Three: The current density was mistakenly computed several ways. Please see the posted solution.

Comments on Homework #7
The only common problem is 2(d) where a lot of students thought that "phasor form" is "vector form."

Comments on Homework #6

1.b. A number of students only got the first frequency (9.4MHz). A few students used the speed of light in vacuum (c) rather than the speed of light in the material (v) to obtain the wavelength.
Many students did not have the correct answer for Vmax and Vmin.

Comments on Homework #5

1.a. For the long straight wire, remember that the magnetic field outside of the wire (which we use to determine the external flux) extends all the way to infinity.
1.b. To show that your answer is the same as the one in the back of the book, you need to simplify the answer given (not your answer) for the case where b << a. The best way to do this is to apply the binomial theorem approximation for the square root. The square root of (1+x) where x is much less than 1 is equal (approximately) to 1+(1/2)x. Try it out if you don't believe it. If you cannot figure out how to do it this way, just show that your expression agrees with the answer in the back when a = 10 and b = 1. Be sure you mention which approach you are using.
1.c. No hints should be necessary.
1.d. Remember to be sure that you use the total flux linked by the second coil when determining the mutual inductance, not just the flux in a single cross-section. When writing this question, I probably should have called the integral I have given the flux integral, not the integral for the flux linked by the circuit.
2.a. To find the flux linked, you just need to integrate the expression for the induced voltage.
2.b. Since you know the flux linked as a function of time from part a, you should be able to figure out the flux in a single cross-sectional area and thus the flux density B as a function of time.
2.c. The peak in the voltage signal will correspond to the peak in the radial compnent of the magnetic field.
2.d. You have the axial magnetic flux density as a function of time in part b. Now you only need to use t=z/v to rewrite your answer in terms of z.
2.e.f. I hope you do not need hints for these questions, since we went over them in class.

Common Problems on Homework #4

Question 1e -- Some students did not realize that the magnetic flux asked for was the total flux throug the specified region. That is the limit of the integrals should have been from 0 to a for the region r Question 2e --Those students who understood the configuration of the Saddle Coil did this problem pretty well. Some got confused about where the current was carried.
A general problem -- Many students do not realize that the magnetic field unit for B is Tesla. They simply let H equal 0.2 Tesla. The term "magnetic field" generally refers to both B and H. H is specifically called the magnetic field intensity and B the magnetic flux density. However, B is most often called the magnetic field, even though the textbook saves that terminology for H.

Comments on Homework #4

In the first problem, be careful to use the correct areas when finding the magnetic field and the magnetic flux. In Ampere's Law (used to find B or H) the area of interest is one that current passes through. To determine the magnetic flux, the area of interest is the one the magnetic field passes through.
In the second problem, be sure that you begin by writing the magnetic field inside a circular wire. Then convert this expression (most importantly the unit vector) into rectangular form. Once you have the field expression in rectangular form, you can write the field inside each of the two currents we are using to find the total field. Finally, the field of interest is in the region where the two currents overlap and thus there is no net current. Big Hint: If your final answer is at all complicated, you have not done this problem correctly!
The last part of question 2 is conceptually more difficult so I don't recommend spending tons of time on it. There are several methods that can be used to solve this problem. If you like trigonometry, you should try to figure out the current carrying area by drawing some pictures. If you prefer brute force integration, set up the area integral in a manner similar to what is found in Chapter 2 of the text and then use Maple to evaluate it. I found that both techniques worked pretty well.
One dimension was left out of the problem description. To keep this problem simple, assume that b=1cm in part e.

Common mistakes on homework #3

Question 1e -- Most students did not realize that the total surface charge density consists of two different parts. Many students only computed the surface charge density either just in the air or the dielectric.
Some students did not set up the open parts of the boundary correctly. Remember that the equipotentials must be horizontal here.

Common mistakes on homework #2:

Voltage was not treated as a voltage difference. Remember that voltage is not uniquely defined unless we specify where it is equal to zero.
Incorrectly integrating the electric field to obtain the potentail as a function of position.
Incorrectly adding vectors. Remember that vectors must be added component by component. One cannot just add the magnitudes to get the total.

Common mistakes on homework #1:

1(d): Most students got the total current by evaluating the integral from 0 to a instead of from 0 to r and then noting that J=0 for r>a. It is important to show procedures in detail on homework assignments, so you don't have to guess what you did when you study for quizzes. This time, credit was given even if the work was not thorough, if the answer was correct.
2(b): Again, the mistake was similar to 1(d).
2(d): Some students do not realize that the gradient operator produces a vector. They are also careless with notation and have expressions with scalars being equal to vectors. Be sure that you use vector notation correctly.
1(a): A few students were confused by the surface diagram given in the problem and plotted J(r) vs z instead of J(r) vs r.

Reading from the Class Notes

Suggested reading from Paul, Whites and Nasar is listed on each lesson sheet. You should also be looking at the corresponding pages in the class notes: (1.1) None; (1.2) I-1 to I-14; (1.3) II-39 to II-44; (1.4) II-26 to II-34; (2.1) I-16 to I-24; (2.2) I-24 to I-29 and II-1 to II-10; (2.3) II-10 to II-26; (2.4) III-1 to 30 and IV-1 to IV-6; (2.5) IV-6 to IV-30; (2.6) II-35 to II-39, V-1 to V-7 and V-27 to V-33 and (2.7) V-8 to V-27. Readings for the remainder of the lessons will be posted later. Be sure that you purchase the notes as soon as possible.

MathCAD Info

The MathCAD Explorer and the Visual Electromagnetics Workbook we use in class can be downloaded from the web. Please see the bottom of the main Class Information Page under TEXT.

Prep Assignments and Homework

Preparation/Homework assignments are posted on the Handouts page. Both the prep assignments for each class and the corresponding homework assigment are included.

Handouts

PDF versions of most course handouts will be available on the handouts page. (Accessible from home page ). You can also access many of them from the course schedule page.

Quiz Grades

Quiz 3 also worked out well! The grades were pretty high (the median and average were both about 84-85), so the grade distribution was very simple. A: 90-99, B: 80-89, C: 70-79, D: 60-69.

Quiz 2 worked out more-or-less as I had hoped. The grade distribution is as follows: A: 90-100, B: 76-89, C: 62-75, D: 52-61.

Quiz 1 was a bit longer than I had intended it to be. Thus, the grades were a little on the low side. The grade distribution is as follows: A: 86-97, B: 65-84, C: 50-64, D: 40-49.

Quizzes

All quizzes will be held in Ricketts 203.

There will be three quizzes during the semester on the following Wednesdays from 7-9pm: 2 February, 1 March, 12 April.

Quiz 1 comes a week earlier than usual this semester. Thus, less material will be covered than in the two Quiz 1 examples included in the class reserves. Specifically, for Quiz 1 from Spring 1999, you will NOT see the material in problem 1, problem 3d&e and the problem 4 Poisson solution option (you can expect to see a problem like this, but you will be asked to do it using Gauss' law). For Quiz 1 from Fall 1999, you will not see the material in problem 1 b&d, problem 2 and problem 3d. These questions have to do with either solution of Poisson's equation or capacitance. The quiz this time will cover all the material we have addressed through lesson 2.4. Remember that the reading assignments are included with the lessons. We will review for the quiz on Monday.

The quiz will be about half short questions (see Quiz 1 from Fall 99 for examples) and half long problems like the ones you have seen on the homework. The long problems will not be so mathematically involved, since the quiz is only 2 hours long. There will be about 10 short problems and 2 long problems.

After seeing how far we got during class today (31 January), I decided I need to restrict a bit further what will be included on Quiz 1. The following are what you can expect to see related to materials and fields:

You should know the range of possible values for typical dielectric constants and dielectric strengths. The table on Electric and Magnetic Material Properties found in the Supplementary Materials page has such information. I don't mean that you have to memorize specific numbers, only have a sense of what the properties of dielectrics are relative to air. That is the dielectric constants should be greater than for air by about 1 to 10 and dielectric strength should also be larger than for air.
The application of boundary conditions at the boundary between two dielectric media, similar to Example 3.16 in the textbook or problem 1a of the fall 99 Quiz 1.
A Gauss' law problem that includes one or two dielectrics (equation 93 in the textbook), like Example 3.17 in the textbook, problem 4 of the Spring 99 Quiz 1, or Problem 2 of lesson 2.4. The latter problem is also solved in pages II-8&9, III-17, and III-25-30 in my class notes. In my notes, I also find the capacitance (which you can ignore) and I use both a surface charge and a line charge representation. In these examples, only parallel plate and coaxial structures are considered. It is also possible to do this problem in spherical coordinates.
The application of boundary conditions at the boundary between a dielectric and a conductor (equation 92 of chap 3 in the textbook). That is, given the surface charge density, figure out D or given D figure out the surface charge density.

Quiz 2 will cover the material from lesson 2.5 to 3.6. Like Quiz 1, this is different than last semester. Thus, the questions from last semester's quizzes that you should study to prepare are found in both Quiz 1 and Quiz 2:

Problem 1, parts b (capacitance) and d (the point form of Ohm's Law and the interesting device we saw that is based on capacitance)
Problem 2 (Using a spreadsheet to find the electric field and capacitance)
Problem 3, part d (capacitance of a structure with more than one dielectric)

Problem 1, parts a (boundary conditions), b (Faraday's Law for moving coils or magnets), c (toroidal inductor), d (Forces on current carrying wires in magnetic fields -- even though this is a question we will address in more detail when we do the project on this motor, the general concept of a force on a current carrying conductor or on a moving charge can show up on this quiz), e (resistance of a conductor) and f (some kind of extra credit questions will be included)
Problem 2, parts a-d (finding current distributions and determining the resulting magnetic field). The energy question (part e) will not be included. You could be asked instead to find the flux in the region between the wires and then find the inductance per unit length from the flux.
Problem 3 will not be included. We do not get to magnetic circuits until after the quiz.
Problem 4 -- This kind of problem you can expect to see.

Like Quiz 1, the quiz will be about half short questions and half long problems like the ones you have seen on the homework. The long problems will not be so mathematically involved, since the quiz is only 2 hours long. There will be about 10 short problems and 2 long problems. Some extra credit questions will also be included.

Quiz 3 will cover material from lesson 3.7 to 5.2. The quiz will be about half short questions and half long questions, like the other two quizzes. The questions will emphasize transmssion lines more than magnetic fields, although there will be questions on magnetic field energy and magnetic circuits. Also, there will be questions (short ones) on the two projects. The following questions from previous quizzes are similar to what you will see on this quiz:

Problem 1 - Pulses on Transmission Lines
Problem 2 - Electromagnetic Waves (This question will be asked mostly in the context of an analogy with voltage and current waves on a transmission line. The table handed out in class on Monday, 10 April shows what we mean by an analogy where, for example, voltage V is replaced by electric field E, etc.)
Problem 3b - terminations, 3c - VSWR
Problem 4 - Sinusoidal steady state waves on transmission lines.

Problem 2e - energy in a magnetic field (could also be asked to determine inductance using the energy method)
Problem 3 - Inductance from magnetic circuits

Problem 1b - Pulses on Transmisson Lines, problem 1d&e -- transmission lines.
Problem 5 - Sinusoidal Transmission Lines
Problem 6 - Pulses on Transmission Lines

Beakman's Motor
Channel Blocker