Day 50: Electric Potential Practice

I was home sick today and provided AP Physics 2 with a series of practice problems to work on individually and then confer with their group. I would have otherwise incorporated these problems into peer instruction. Most of the problems were from the Ohio State University PER group. It will be interesting to compare how they justify their answer to a question like the following based on what they’ve explored so far and how that changes after they complete the mapping electric potential lab and visualize electric potential surfaces.

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  ##electrostatics  

Day 49: Electric Potential

Today in AP Physics 2, we built upon our understanding of electrical potential energy to explore the concept of electric potential. I continued the strategy of minimizing lecture and having students work through various ranking tasks (from Knight’s Five Easy Lessons like last time). We’re spending more time on these concepts, and students appear to be developing a deep conceptual understanding of these concepts.

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Day 48: Why Fields?

Today my AP Physics 2 students whiteboarded electric force and field problems while I was gone at the Science Curriculum Team (SCT) meeting. The SCT is creating a new 6-12 science curriculum aligned with the Next Generation Science Standards. My group within the SCT was focused on the curriculum for a junior-level physics course. We previously identified fields as the central concept of one of the units. However, we were struggling with how to present fields to a regular physics class in such a way as to have students appreciate the necessity of a field model. After much discussion, we finally arrived at a compelling question: when you lift an object, thereby transferring energy into the system, where is that energy stored?

  ##ngss ##whiteboarding ##representations  

Day 47: Electrical Potential Energy

Today in AP Physics 2, we began to investigate the concept electrical potential energy. It is important that students have a strong understanding in electrical potential energy before we start to investigate the concept of electric potential. While students are familiar with other forms of potential energy (gravitational, elastic), a couple of aspects of electrical potential energy provides a challenge. One, unlike gravitational potential energy, the electrical potential energy depends not only on the position of the particle in the field but on the sign of the charge of the particle as well. Two, negative electrical potential energies are quite common. While “zero” gravitational potential energy could be defined such that negative gravitational potential energies are considered, students rarely encounter this in their first-year course.

Students spent most of class today, thinking through the following nine scenarios (from Knight’s Five Easy Lessons) and whether the electrical potential energy of the particle increases, decrease, or stays the same from the initial point to the final point; first individually, then among their groups, and finally as a whole class. It was fantastic to hear students justify their answers in terms of energy conservation, work done on the particle, and the relationship between the direction of displacement and force.

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Day 46: Fields Video and Quiz

Based on the recommendation of a student, I showed the class this excellent video on fields produced by Minute Physics:

It introduces the concept of fields and the historical background of the discovery of that model, even introducing the concept of scalar and vector fields. I love the particles of cheesecake passing through space field! It also serves to introduce the class to Minute Physics if they are not already familiar. (Although I hope by now that they all are!)

Students completed a practice quiz on the concepts of electric forces and fields. I need to follow up with a handful of students who struggled on the quiz and ask if they are struggling to understand the concept of an electric field or if they didn’t carefully read one of the questions and thought they were to be solving for the electric force instead of field.

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Day 45: Electric Fields

Today, we built upon the computational models for Coulomb’s Law which essentially became electric field vector diagrams. Historically, students have struggled to develop a deep understanding of electric fields. In the past, I used to “cover” electric fields in our first year course. I found that in AP Physics B, students retained little understanding. The past couple of years, I have introduced fields using the recommendations in Knight’s Five Easy Lessons; specifically, page 207-208. I’m impressed by how much discussion and learning can be achieve related to this simple diagram:

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As recommended in the book, I ask students to draw the corresponding electric field vectors at each of the three points. I then point to the middle of one of the vectors and ask them if an electric field exists at that point and, if so, what is its direction. Finally, I ask them to draw force vectors for charges of different signs and magnitudes at the points. This sequence of questions seem to address many of the common misunderstandings regarding electric fields.

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Day 44: Bridge from Coulomb’s Law Computational Model to Electric Fields

Today, we started class with students sharing their computational models. I then used one of the students models that attached a vector for the net force to the point charge to illustrate how their model showed the direction and relative magnitude of the electric force at every point through which the point charge moved. I then asked what we could do if we wanted to know the direction and relative magnitude of the electric force at every point around a charged object. Once they said that we would need a lot more point charges, I showed them this model:

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While tomorrow’s lesson will formally introduce the concept of the electric field and its relationship to the electric force, I did use this model as a bridge by introducing the visual of electric field vectors. I also showed them another model with multiple charged objects to demonstrate that the electric field vectors represent a superposition of the electric force due to each charged particle:

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I tried to write this model in a fairly extensible manner to make it easy to model various configurations of charged objects.

  ##electrostatics ##representations ##tech ##glowscript