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Physics C: Electricity & Magnetism Course Perspective
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by HughHenderson
Director of Science Curriculum
Plano Senior High School
Plano, Texas
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| | Please note: The official College Board® Course Description is available below in "More."
On the first day of school I ask my students what they think is the most important word in the English language. After we discuss a few possibilities, I suggest that the word is "relationship." Every thought and action carried out in our minds and lives boils down to a relationship between two things. We're never interested in just one thing; always in how that one thing relates to another thing. Then I suggest that the second most important word in the English language is "change." Once we establish a relationship between two things, like displacement and time giving us velocity, we want to know how that relationship changes, in this example, acceleration. Physics is the study of relationships, which we sometimes call equations, and how those relationships change.
AP Physics C is a calculus-based physics course principally taught to students who plan to major in physics, astronomy, mathematics, or any type of engineering. It is typically taught as a second-year course covering mechanics in the first semester and electricity and magnetism in the second semester. The AP Physics C Exam is actually two separate exams, with one covering only mechanics and the other covering electricity and magnetism. The two exam scores are reported separately, and the student can earn credit for one or both.
In teaching electricity and magnetism, I like to focus on the word "symmetry." I show the students the symmetry between gravitation and electrostatics in concepts such as mass and charge, gravitational field and electric field, gravitational potential and electric potential, and Gauss's law for gravitation and Gauss's law for electricity, two laws that earn their living by utilizing symmetry. I spend most of the time in electromagnetism developing and using the four Maxwell's equations (Gauss's law for electricity, Gauss's law for magnetism, Ampere's law, and Faraday's law of induction), all of which depend heavily on symmetry. Meaningful labs can sometimes be scarce during electrostatics, but there are many of them to be done when we cover circuits. I have the students study series and parallel circuits and Kirchhoff's laws by hooking up batteries, light bulbs, resistors, ammeters, and voltmeters. Then it's just a few more concepts and equations to add capacitors and inductors to the circuit. Although these are never shown in the same circuit at the same time on the problems of the AP Physics C Exam, it sure is fun to cap the semester off with the symmetry between the differential equation for an inductor-capacitor circuit and the differential equation for a mass vibrating on a spring.
If the students have already had a year of introductory physics, they have probably done all the typical first-year labs. There is less time in AP Physics to do labs, since so much time is spent on conceptual development and problem solving, so when you have the students do labs, make them count. The students need to be able to take data, with or without high-tech probes and software, organize the data, analyze the data and sources of error, draw conclusions, and explore ways to improve or extend the experiment. I guide my students in such a way that they design the procedure of the labs themselves. I tell them what equipment they have available to them and what it is I want them to measure, and let them go. I have found my students really enjoy the freedom to be creative in the lab. Many of the usual first-year introductory physics labs can be refitted for an AP class by extending them and letting the students decide how the measurements will be made. In addition to problems on the AP Exams, there are also lab-based questions that ask the students to design and analyze a procedure to measure something. Examples of these lab-based questions can be found in the last three years' free-response questions, which are posted in the Exam section on AP Central. Currently, a lab guide is being developed that discusses the types of labs that have been helpful to the students' understanding of physics and success in introductory college-level courses.
Finally, don't try to develop an AP Physics course all by yourself from scratch. There are many resources to help you find the pacing and methods that work best for you and your students. The AP Physics Teacher's Guide, the AP Central Web site, and the regional offices are very helpful, but colleague support is invaluable. You should attend one-day and two-day workshops and five-day institutes, where you can find experienced AP Physics teachers who are happy to help you develop or update your course, along with other participating teachers who may be at the same point you are in developing the course. There's no better support team than other physics teachers, and you'll find that they'll go the extra mile to help a colleague. The content in AP Physics can be very difficult, and it may take you a few years to feel comfortable with the material, as it has me, but don't get discouraged. Develop a good relationship with your students; let them know that you don't have all the answers, but you care about their progress and you're willing to work with them if they are willing to work with you.
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