Chapter 19, Problems 9-12

Chapter 19, Problems 5-8

Chapter 19, Problems 1-4

In the first problem, the range between maximum and minimum comes from the relative direction of the magnetic field and the electron's motion.

Practice Chapter 15

Every problem in SV8 Chapter 15 is in that assignment. Scores will not be counted towards your grade - the problems are for you to practice is you want. This thread is a place to discuss any of those problems. In referring to any problem here, please identify it with the information that is at the right side of the blue bar above the problem, e.g., SERCP8 15.P.018.

Practice Midterm Exam

This thread is for discussion of problems in the practice midterm exam, which is posted in Blackboard in Course Documents.

Lab 3 pretest is now available

I posted the announcement for the Lab 3 pretest availability for all PHY 124 sections and sent it to each of your email addresses (the ones that Blackboard accesses). As usual, the pretest assignment will be available to you until your lab section begins.

Prof. Koch

Chapter 18, Problems 10-12

Problems with resistors and capacitors, from Section 18.5.

Chapter 18, Problems 7-9

These problems require application of Kirchhoff's rules for more complicated DC circuits. See section 18.4

Chapter 18, Problems 1-6

These problems pertain to sections 18.1, 18.2, and 18.3. You should be able to deal with all of them using combinations of series and parallel resistors.

Note that question 4 part C asks for the power delivered by the battery, but the dimension given with the answer is Amperes. That should be Watts. (Doesn't affect how you approach the problem -- I just mention it to avoid possible confusion.)

Chap 17, Problem 12

This problem is a bit tricky. Start by drawing a diagram, and note that the question asks for the power delivered to the cleaner, which would exclude power that heats the extension cord.
Also, see my latest post about the need to calculate intermediate results to an accuracy much better than 1%. You should be safe with six significant digits as you are working.

Chap 17, problems 9 - 11

Problems from SV8 Section 17.6. The language of #10 (Problem 17.36) is a bit ambiguous. Part b should say, "What percentage of the power generated by the power station does this loss represent."

Chap 17, Problems 7 and 8

Problems from Section 17.5.

Chapter 17, problems 4-6

These problems are from Section 17.4. For the fifth one (SV 17.12), you might find yourself with two equations involving length and area of the wire: the given mass gives you L*A, and the resistance gives you L/A. Multiply those two equations together and it eliminates A.

Chapter 17, Problems 1-3

For 2 and 3, you need to convert a given mass or density of metal to charge or charge density. I think it's easiest to visualize this as a unit conversion problem, for example, the density of Al is 2.7 g/cm^3, which you want to convert to electrons/m^3. So multiply by unity in various forms to clear the dimensions. For example (1 mole / 27 g of Al), (How many atomis is it? / mole), (conduction electrons / atom), ...

Lab 2 pretest is now available

Please see the Announcements web page in Blackboard for your PHY 124 lab section. To avoid clutter, I took down the previous announcement about the Lab 1 pretest. The Lab 2 pretest announcement will remain up for each lab section until that section meets to do Lab 2. I'll do the same for future labs. As I did for Lab 1, I sent the announcement via email to each student in each section. If you did not get it, something is not right with your email. This could be that the University does not have the email address that you are (now) using. It's up to you to correct this. Instructors using Blackboard to send email to students do not see the email address being used for each student.

Chapter 17

I'll break this up into more threads soon, but if anybody is getting a head start, there are a couple of things I want to point out. In a couple of problems, you will need to find densities, atomic numbers, etc. of certain elements. This kind of info is readily available on the web, and you have a periodic table with some of this info in the back of your book. Likewise, the book contains a table of resistivities and thermal coefficients of resistivity (page 577).
The statement of part of the 10th question (SV8 17.36) is poorly phrased; part b) should read, "what fraction of the power that is generated at the power station does this loss represent."
Careful with dimensions throughout. Look at the dimensions furnished with the answers. millimeters, micrometers, percent, ...

PHY 124 Lab 1 pretest

Students (and TA staff) in all lab sections should have received email on Tuesday (7 Sept) night about the Lab 1 pretest being posted in the Assignments section of Blackboard for your lab section of PHY 124. The email was the same Announcement that also appeared on Blackboard. I know that many of you have logged in and at least started the Lab 1 pretest, which exists within the Maple TA "plugin" for Blackboard. There are 5 multiple-part questions in the pretest; each question is worth a maximum of 7 points, giving 5x7=35 points maximum in all. Partial credit is given for partially correct answers, but there is no limit on how many times you may re-do the pretest. You may check how you did on each question, and when you're done with an attempt on the whole pretest, you may check your overall grade for it. I logged in as a student, took the pretest, and did all of these steps. So far, as the instructor I am able to monitor how many students are logged in on the pretest for each section, but a software glitch prevents me from seeing the pretest grades for each student. The Blackboard support staff is now working to correct that.

Make sure you do not wait until the last minute to complete the Lab 1 pretest because, as was contained in the Announcement/email, you will cease to have access to the pretest at the time your lab section begins.

Good luck!

Prof. Koch

Chapter 16, question 12

This question, SV8 problem 16.52, has some problems in its wording. First, the capacitor is made from two strips of aluminum foil, separated by paraffin-coated paper. The question wants you to think about the capacitor unrolled, so that there are two flat plates, separated by one layer of the dielectric. What are the dimensions of that configuration in order to have the given capacitance? (Then, as an editorial note, the statement of the problem goes on to say that if you put in another piece of paper and roll the thing up as illustrated, it will actually have twice the capacitance because now charge accumulates on both sides of each plate, essentially doubling the active area.)

Chapter 16, questions 10, 11

These two questions refer to material in SV8 section 16.9.

Chapter 16, questions 7-9

These two questions come from SV8 sections 16.6 and 16.7.

Chapter 16, Questions 3 through 6.

These questions are from SV8 sections 16.2, 16.3, and 16.4. Please try to look at them before the September 7th class.

Chapter 16, Questions 1, 2

Remember that this homework assignment is due on Wednesday, September 15th at 5:00 PM.
This thread is to discuss the first two questions, which come from SV8 section 16.1

Chapter 15, questions 10-12

These three questions are from SV8 sections 15.6, 15.8, and 15.9. The whole assignment is due on Tuesday, September 7th at 3:30 PM.

Chaper 15, questions 5-9

These five questions are from SV8 section 15.4. The whole assignment is due on Tuesday, September 7th at 3:30 PM.

Chapter 15, Questions 1-4

These four questions are from SV8 section 15.3. The whole assignment is due on Tuesday, September 7th at 3:30 PM.