General College Physics

Wisconsin Lutheran High School

Week 26 (Feb. 17 - 21)

Reading: Current and resistance (Chap. 27)

Key Topics: electric current, resistance, resistivity, ohm's law, joule heating

Week 26 Homework Problems:

Electron accelerator: Suppose that two large parallel plates are connected to a 1 kilo-volt power supply so that the left plate is maintained at an electric potential of +500 volts and the right plate is maintained at an electric potential of -500 volts. The plates are separated by distance of 1 mm. (a) First, sketch the electric field in the region between the plates. (b) What is the strength of the electric field between the plates? (Answer: 1000 volts / 1 mm = 1,000,000 volts/meter) (c) If an electron is placed very near the +500 volt plate, what is the force exerted on the electron by the electric field? (Answer: the force is just the electric field times the electron charge. This gives 1.6 e -13 Newtons) (d) How much work does it take to move the electron from the +500 volt plate over to the -500 volt plate? (Answer: this is the force times the distance. It is 1.6 e-16 joules) (e) If the electron, placed near the -500 volt plate is released, what will be its acceleration toward the +500 volt plate? (Answer: the acceleration is the force divided by the electron mass. it is a =1.76e17 meters/second^2) (f) what will be the electron's speed just before striking the +500 volt plate (Answer: using conservation of energy, we can set the work equal to the change in kinetic energy. This gives v =1.88 e 7 m/s )?
Power lines: High-voltage power lines deliver electrical current to your neighborhood. The aluminum wire used for these lines has a cross sectional area of about 5 square centimeters. What is the resistance of ten kilometers of this wire? (Answer: resistivity of aluminum * length / area = 0.52 ohms ) Hint: you will need to look up the resistivity of aluminum.
Car battery: A car battery has a rating of 220 ampere-hours. This rating is an indication of the total charge that the battery can provide to a circuit before failing. What is the total charge (in coulombs) that this battery stores? (Answer: an ampere is a coulomb per second. So 220 ampere-hours * 60 minutes/hour * 60 seconds/minute = 792,000 coulombs). What is the maximum current that the battery can provide for 38 minutes (Answer: 792,000 coulombs / 38 minutes = 347 amperes).
Mystery resistor: The current in a series circuit is 15.0 amperes. When an additional 8.00 ohm resistor is inserted in series, the current drops to 12.0 amperes. What is the resistance of the original circuit? (Answer: Since the voltage didn't change, the product of the current and the resistance remains constant. Thus, 15 amps * R = 12 ams * (R + 8). Solving for R gives R = 32 ohms)

General College Physics

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Course syllabus

General College Physics is a year-long introductory college-level course for advanced (typically junior or senior level) students at Wisconsin Lutheran High School. It is a dual-credit course offered at Wisconsin Lutheran High School in collaboration with Wisconsin Lutheran College. This means that students enrolled in the course have the option of receiving credit for a four-credit algebra-based laboratory science course from the College.

During the first semester, we will primarily study the science of motion and its relationship to forces. Topics include: dimensional analysis, measurement, uncertainty, estimation, 2 dimensional kinematics, projectile motion, newton’s laws of motion, force diagrams, centripetal force, circular motion, conservation of energy and momentum, torque, angular momentum, oscillations, and gravity. During the second semester, we will explore a number of inter-related topics including: heat, thermometry, the laws of thermodynamics, electricity, magnetism, optics, electromagnetic induction, radiation, atomic theory, and nuclear physics.

Emphasis on theoretical topics, careful thinking, laboratory experiments, and problem solving makes this course challenging. My aim is to help you succeed in this course, and to have fun while learning physics. So please do not hesitate to contact me with any problems you may run into this semester!

Course textbook: The course will be organized around a book: the Pocket Guide to accompany Physics for Scientists and Engineers (4th edition) by Serway. (I’ll call this PSE for short.) I would highly recommend obtaining a copy of this book. It is inexpensive, compact, and well-written. It will make a very handy addition to your home science library. If you don't want to buy it, I will have copies to loan out for the semester.

Course time and location: The course meets on a rotating schedule in WLHS 223—the science wing on the first floor of WLHS.

Professor: Dr. Kuehn from Wisconsin Lutheran College (WLC) is the professor for this course. Contact info: kerry.kuehn[at]wlhs.org

Registration for College Credit: Wisconsin Lutheran College is requiring students in this course who are interested in obtaining college credit. Please apply in the application link below for each class you are wishing to apply for college credit. This must be approved by Friday, September 27.

https://admissions.wlc.edu/register/foundations

Once students apply we will wait for Wisconsin Lutheran College to confirm eligibility and requirements for college credit and communicate out further information. Please reach out to Mr. Davis if you have any questions.

Teaching Assistant contact info: The Wednesday course sections (beginning in September) will be overseen by a teaching assistants. Alyssa Ebeling is an upper-level physics major at Wisconsin Lutheran College. Contact info: alyssa.ebeling[at]wlc.edu

Course websites: In addition to the course information provided through WLHS’s OnCampus system, we will be also using a website I’ve designed for this course: www.greatphysics.com/WLHS/

Homework exercises: I will assign weekly homework problems. These are designed to deepen your understanding of lecture material and to prepare you for the quizzes and tests. I do not intend to grade your homework solutions; I will merely give you credit for handing in your best attempt by the due date. Late work will receive reduced credit.

Laboratory exercises: Some of our weekly assignments will include laboratory work. Labs will typically take up at least two class periods. Your laboratory notebook pages must be submitted by the assigned due date. More details about the required format and expectations will be discussed before the first laboratory period. You will need to order/purchase a dedicated laboratory notebook. Here are guildlines on what to include in your laboratory notebook.

Quizzes: We will have in-class quizzes almost every week on Monday. To prepare for quizzes, you should read the assigned book chapter (at least once), review the lecture material, complete all of the homework problems, and review the homework solutions.

Tests: We will have a midterm exam before the end of the first (and third) quarters and a comprehensive final examination before the end of the second (and fourth) quarters.

Software: Logger Pro 3.15 Is an excellent data analysis software package. Download for Wndows 10, 8.1, 7, and for macOS 10.14, 10.13, 10.12, 10.11, 10.10. For more details on how to download and install Logger Pro click here.