Announcements

. Announcements

Announcements

Review Sessions

There will be two review sessions for the final exam, Monday at 5 pm and Tuesday at 2 pm in the Instrumentation Studio.

Extra Credit

There are two projects that can be completed for some extra credit points. Just exactly how these points will be added to the overall course grade has not yet been determined. This policy should be posted in a few days. The two projects are:

Graphics -- Some of you who are very good at creating graphics images, can earn some extra credit points by creating some drawings for the standard electric, magnetic and electromagnetic field configurations seen in this course. These include, but are not limited to, coaxial cables, toroidal and solenoidal inductors, etc. If you wish to do this, please sketch out your ideas on paper first and get them approved before proceeding. The sketches should include more than one view, dimensions, labels for materials used, etc.
Design Project -- A very simple device can be built in a few minutes that is capable of launching a piece of a paperclip at least several feet. An old description of this project can be found at Bonus Design. An updated version of this will be made available shortly.

Quiz 1&2 Grades

For Quiz 1, including the re-grade of problems 3 and 4, A: 83-96, B: 70-82, C: 60-69, D: 50-59. For Quiz 2, A: 90-105, B: 80-89, C: 65-79, D: 50-64.

Comments on Quiz 2

Be sure that you understand when you need to integrate and when you don't. This is still the most common mistake in solving either electric field or magnetic field problems.

Variations of the questions from Spring 99.
Variations of the homework questions, particularly the ones that can be completed in less time.
Prep assignment questions. These will mostly be found in the short answer section of the quiz.
Fundamental concepts encountered in the design project. For example, determining the forces when you know the magnetic field and the current in a wire.
The sections of the book to be covered are Chapter 4, Section 5.1 and Appendix B. The key topics from each section are:
- 4.1.1: Calculate resistance of conductors with constant area or an area that varies along its length.
- 4.1.2: Apply conservation of charge or the continuity equation to some simple configuration.
- 4.2: We will not use this material directly, only to determine the direction of the force between conductors.
- 4.3: Be able to apply the Lorentz force equations in either the JxB or vxB forms to find the forces on conductors or moving charges. The magnetic flux density or field due to a long straight wire. (This is something worth memorizing, since so many magnetic field configurations have straight current-carrying wires.) The method used, however, will not appear on the quiz. This field can be determined much more easily with Ampere's Law. The field due to the sheet of current is also important, but more readily determined using Ampere's Law. What is important about the Biot/Savart law is its usefulness in determining the direction of the field. This is definitely something you should know how to apply. There is a problem on this topic in the Spring 99 Quiz 2 prep info on reserve.
- 4.4: Ampere's Law provides the main technique we apply to find the magnetic field. Be sure that you understand it in both its integral and differential form. The first problem on Homework 4 is a good example. Be able to apply it to the long straight wire, the sheet of current, the solenoid, the torus, the parallel plate stripline, the two wire line and the coaxial cable. All have been addressed in a homework assignment or last spring's quiz.
- 4.5: Flux plays about the same role for inductors as charge does for capacitors. As such, you must know how to determine it once you have an expression for either the magnetic flux density B or the magnetic vector potential A. You should also understand how to apply the conservation law for flux (Gauss' law for magnetostatics) to simple configurations.
- 4.6: The key topic here is permeability. You will not be asked to do any problems based on the physics of magnetic materials. However, you should have a basic understanding of how materials can affect an applied field. My notes have a good discussion of this and the picture in figure 4.25 is also helpful.
- 4.7: The boundary conditions are very, very important. They are the kind of concept that I sincerely hope you take away from this course and use in the future. The methods we have learned for finding B and H are of limited use in real world problems, but boundary conditions are always simple to apply. Example 4.13 is very good.
- 4.8.1: Inductance is another key concept. You should understand how to determine it using both the flux method of this section and the energy method of 4.9. Example 4.16 is very important, since it introduces the concepts of internal and external inductance. Internal inductance is much easier to determine using the energy method, so do not worry that you will have to use the method of this example. However, the external inductance solution is useful.
- 4.8.2: Here is where the technique is developed for finding the resistance of a condutor with varying properties and geometry. You will not be asked to apply the general concepts here. However, as noted above, you should be able to figure the resistance of a conductor whose area varies along its length.
- 4.8.3: We did address the topic of power density. However, you should understand it, since it provides a connection between fields and circuit concepts.
- 4.9.1: Be able to determine the energy stored in a magnetic field.
- 4.9.2: Use the energy stored in the magnetic field to find inductance. The coaxial cable example (4.20) is very important.
- 4.10: The magnetic circuit concept is a good practical way to estimate the fields and inductances of many different configurations in which magnetic materials are used. You should know how to apply it to a torus like in figures 4.42 and 4.43 or combinations of straight core pieces like in figures 4.44 and 4.45
- 4.11: Force calculations will be done only using the magnetic pressure concept rather than the more complicated analysis of this section.
- 5.1: Be able to apply Faraday's Law to problems like in examples 5.1 and 5.2.
- 5.2: Be able to apply Faraday's Law to problems like in examples B.1 and B.2. You should be able to recognize such problems from the old quiz.
I strongly recommend that, as preparation for the quiz, that you draw all of the basic magnetic field geometries, showing the wires/currents and material boundaries and some typical magnetic field lines. It is very important that you develop your ability to visualize these problems.
This list will probably be updated based on ideas from students and course staff that come up before next Wednesday.

Special Prep Assignment for Monday, 25 October

Read over problem 1 of lesson 3.6 in which a toroidal core is added around a long straight cylindrical wire. From the information provided, determine the additional inductance caused by adding the toroid. Don't try to figure out the inductance per unit length of the wire since it will be infinite. Rather, figure out the inductance of the core region, with and without the core material and take the difference. You might find it easier to use the energy method, but you can also use the flux method if you prefer. An approximate answer will suffice.
Read over problem 2 of lesson 3.6. Write out the general expressions for the boundary conditions used in this problem. Then solve the same problem for the case where the permeability of the iron is assumed to be 40 times that of air, rather than 5000. Then draw a diagram of the vectors at the boundary like the one given in the problem. The same kind of diagram is drawn for similar problems in figure 4.30 of the text. Give the B field vector in iron a length of 10 cm and then draw the correct length and orientation for the vector in air that satisfies the boundary conditions. The lengths of the vectors should be proportional to their magnitudes.
Determine the reluctance of the core used in problem 1 of lesson 3.6. Again, an approximate answer will suffice.

Comments on Projects

Project 2 is now available. It is to be worked on over the coming weekend and next week. Monday and Wednesday classtimes will be open shop for this project. You have a choice as to what exactly you will do in this project, so please read the write up carefully.

Project 1 is due on Friday, which is defined as any time before I come to my office over the weekend. If you still need to test a motor on Friday, we will stay around after class until 6 pm, after which no more testing will be possible. The project can be handed in on Monday with a 3 point penalty, Tuesday with a 10 point penalty, or Wednesday with a 20 point penalty. Handing it in will be better than not handing it in, since the projects are 1/7 of the course grade. For your report, be sure that you describe your coil thoroughly and explain your design choices. Also, be sure that you use the information contained in the scope plot obtained to determine the motor speed. Finally, read the project handout thoroughly and address all of the issues listed there. If your group is larger than two people, you only have to do one basic motor test. However, be sure that you have at least two final motor designs and tests if your group size is three or four.

Project 1 involves building and modeling a Beakman's Motor. Please check the Project page for complete info. One important change -- the due date previously posted on the course information page has been changed from 5pm on Wednesday to the beginning of class on Friday.

Comments on Quiz 1

As discussed in class, the results from the last two problems on Quiz 1 were not good. To be sure that everyone in the class knows how to do these problems and to permit everyone to earn some more points on this quiz, all students can redo the last two problems and hand them in on Friday, 15 October. In effect, these two problems are now take home rather than in-class problems. If you choose to do this, you can work with anyone you wish. However, the course staff cannot provide direct assistance and will not tell you if you have the correct answers. You are free to ask us any questions you wish, but we will not answer them if they deal too directly with the quiz questions. Please indicate who you worked with on your solutions to the questions. The additional points you can receive by doing this are determined as follows: Subtract your old total from problems 3 and 4 from your new total. Your additional points will equal the product of this difference times 0.75. Thus, if you had 15 total points before and do the problems completely correctly, your additional points will be (50-15)*0.75=26.

Office Hours/Open Shop

We now have office hours from 4-6 on Tuesdays and Wednesdays in the studio classroom and in the JEC Lounge (3rd floor) from 6:30 - 8:30. Note that we no longer have open shop on Tuesday mornings from 10-12 except by request. Should you need help at that time, please email Azwin by 9 am on Tuesdays. We have our staff meeting at that time and she can stay if necessary. Otherwise, she will in the studio from 4-6 on Wednesdays.

Comments on Homework Assignments

For Homework #4, there are several changes that have been made to make solving problems 2 and 3 easier. Please read over the revised version of the handout posted on the course handouts page.

For the last part of Homework #2, it is not possible to separate the point charges by 45 degrees. The original six charges form the vertices of an octahedron. The only cofigurations that involve more than six charges are icosahedrons and dodecahedrons. The best accuracy (very good in fact) is achieved with the dodecahedron. Configure your charges so that they form the vertices of a dodecahedron instead of trying for 45 degree separation.
You should analyze the six charge configuration by hand rather than trying to write some kind of computer program to do it. However, you can check your results using a Matlab program I have written called buckyoctagon.m which you can find in my public rcs directory. You can use this program as a template for your dodecahedron solution. There is a lot of info available on the so-called Platonic solids in the Supplementary Materials page on the course website. There you should find, for example, the standardized coordinates for the vertices of a dodecahedron.

If you have never transferred files from other people's public directories, there are two simple methods you can use.

Log onto your RCS account. Copy the file from my public directory using the command cp ~connor/public/buckyoctagon.m buckyoctagon.m
Use an ftp program from your pc to go to ftp.rpi.edu Once you are there, change the directory to ~connor/public and you will see the file you need to transfer.

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.

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.

Quizzes

All quizzes will be in DCC 330.

Quiz 1 is on 6 October, Quiz 2 is on 3 November.