Teaching electrostatics in AP Physics 2 completely changed my understanding of circuits- understanding the concept of voltage as the electrical potential difference is a fundamental concept that will be new and uncomfortable for many students. I highly recommend watching or reading as much as necessary to make sure the concepts of electrical potential, electrical potential energy, electric field, and force are completely separate in your brain- because it is sooo easy to get them confused, and how you use the terms will make all the difference for your students! Oh, and this is also a good place for a vector addition review!
Here’s the playlist of videos related that helped me understand! AP Physics 2 Concepts- Unit 3 Electrostatics Playlist Highly recommend Doc. Shusters analogy video- that’s the one that guided the notes!
Demonstrations
I love starting the unit with demonstrations- and these are by far my favorite! It starts with an introduction to the electric force by playing with scotch tape and a balloon and hole punch. In these I emphasize the strength of the electric force- it overcomes gravity easily! Also ask students to explain how the tapes become charged- it leads naturally to the introduction to the triboelectric series and that series of demonstrations. Then, the Van de Graff. I copy the demonstration from this video- Should A Person touch 20,000 Volts? by Jefferson Lab. I try to leave time at the end for students to play with the Van de Graff- some do seem timid about it, but explaining the electrons and safety often gets a couple volunteers!
Ugh the math… but it is rare they will actually see a problem involving complex vector addition- but there are often problems that rely on the concepts. High emphasis on the understanding of how the charges affect the space around them- being clear on focusing just on the force. I recommend not letting students bring in potential or voltage yet- and avoid discussing them yourself, a deep understanding field and force first is best!
PhysicsClassroom Concept Builders- Charge Interactions, Coulomb’s Law, and Electric Field and some of my favorites!
Now for electric fields. In my experience, students assume they understand these because they understand gravitational fields- but while gravity is always in one direction, the electric fields can be positive or negative, which often leads to confusion about the magnitude and strength- be super insistent here that the sign is just the direction of the force, the electric field hockey game helps to anchor this lecture as they move into potential.
pHet Charges and Fields
This is one of the most impactful simulations for students. The visualizations of the field and potential can be brought up and shown throughout the lecture series for this unit, providing a consistent mental image. As is always important in this unit, watch the vocabulary around the simulation- the arrows represent the field, the isolines for potential, the force sensor is the field strength- not the force itself, because that depends also on the test charge in the field.
Now for the most confusing concept- electric potential. I used this video’s analogy- Doc Shuster “Finally, A Useful Explanation of Electric Potential”- to start the conversation, which is the top part of this set of lecture notes. Electric potential is the electrical potential energy per charge- i relate it alot to height*g- the gravitational PE per kilogram.
Capacitors has now been moved to this unit, where it fits much better- it’s always been the bridge between electrostatics and circuits. This helps explain how we can make use of the properties we have been talking about!
At the end of this unit, I give my students about 30-45 min to create a “mind map” of this units concepts and equations. I use chalk markers on the lab benches. This almost always leads to excellent conversations- and I try to emphasize while there are some wrong answers, there’s no right answers- these concepts are all connected. My format works like this:
5 min to write all vocab words and definitions on post its
10 min to work with group of 3-4 students to create draft map
“Cheat time” Send a representative to look another groups model
10 min to add more details, connections
Each group takes 2 minutes to present and share their best connections