The World’s Most Annoying Negative Sign

TL;DR If you want a quick way to gauge whether or not students understand the concept of potential energy, you can ask them to explain the origin of The World’s Most Annoying Negative Sign. It is merely a consequence of the very definition of potential energy, which is almost never explained coherently. In all of […]

Matter & Interactions II, Week 11

More with circuits, and this time capacitors, and the brilliantly simple description M&I provides for their behavior. In chapter 19, we see that traditional textbooks have misled students in a very serious way regarding the behavior of capacitors. Those “other” textbooks neglect fringe fields. Ultimately, and unfortunately, this means that capacitors should not work at […]

Matter & Interactions II, Week 10

Chpater 18. Circuits. You don’t need resistance. You don’t need Ohm’s law. All you need is the fact that charged particles respond to electric fields created by other charged particles. It’s just that simple. When I took my first electromagnetism course, I felt stupid becuase I never could just look at a circuit and tell […]

Matter & Interactions II, Week 7

This week, I was away at the winter AAPT meeting in Atlanta. Students began working on the experiments from chapter 17, which serve to introduce magnetic fields. I want to emphasize some really cool things about the mathematical expression for a particle’s magnetic field: This is really a single particle form of the Biot-Savart law. […]

Matter & Interactions II, Week 6

I’m writing this a whole week late due, in part, to having been away at an AAPT meeting and having to plan and execute a large regional meeting of amateur astronomers. This week was all about the concept of electric potential and how it relates to electric field. I love telling students that this topic […]

Matter & Interactions II, Week 5

This week was all about calculating electric fields for continuous charge distributions. This is usually students’ first exposure to what they think of as “calculus-based” physics because they are explicitly setting up and doing integrals. There’s lots going on behind the scenes though. In calculus class, students are used to manipulating functions by taking their […]

Matter & Interactions II, Week 2

This week was yet another partial week. Between weather and holidays, we’ve not yet had a full week of classes. Such is life I guess. This week, we looked at the electric field of a static particle and the electric field of a fixed dipole on the dipole’s axis and on the perpendicular bisector of the […]

Matter & Interactions II, Week 1

This week was supposed to begin on Monday, but we lost both Monday and Tuesday to snow and icy roads so this week was effectively just a two day week. On Wednesday, I demonstrated Jupyter notebooks and informed the class that effective this semester, we’re moving away from Classic VPython. From this point on, we […]

Conceptual Understanding in Introductory Physics XXIV: Distance Variations of Fields and Forces

This question was inspired by chapters 13, 14, and 15 of Matter & Interactions and would, I think, make a good final exam question even in courses where M&I isn’t used. The story line in those chapters makes a wonderful progression through different charge distributions and their fields and interactions with other similar charge distributions. […]

Conceptual Understanding in Introductory Physics XXIII: A Question About Fields

This question came to me while I was planning for this semester’s introductory calculus-based e&m course (using Matter & Interactions of course). My overall desire and plan is to move away from the traditional number crunching type of problems, where all students really do is manipulate coordinate components of vectors or perhaps vector magnitudes, all […]