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# Reflection on Electrostatics

Lesson 15 of 15

## Objective: Students will look back at this unit and self-assess their understanding of electrostatics concepts.

*80 minutes*

#### Warmup

*15 min*

For today's warmup problem, I've chosen a simple task: to calculate the work done by moving electric charges. My purpose is to underscore the one core idea from the previous lesson: that work can be calculated as the difference in potential energies, even in an electric field. Now, armed with an electric potential energy formula, this task should be simple. As a teaching "hack," I recycle a previous warmup problem by simply adding, in red, some new instructions to the bottom of the page! By re-purposing earlier work, I am able to create a targeted new problem in a matter of moments.

Later in this class, students will be working through a "mock" quiz and doing a lot of computational work. Anticipating that, I want this segment to be a low computational demand on students. My intention is to simply bring the core idea from the previous lesson to the forefront of today's thinking.

Students work individually or with classmates on this problem. I meet with students, working my way around the room to check in about progress and understanding. After five minutes or so, I give students a two-minute warning, alerting them to finish up before reviewing, as a class, the solution to the warmup problem.

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#### Student Demonstration

*10 min*

Prior to this class, students have been preparing simple, short demonstration of electrostatic phenomenon. In a previous class, they rehearsed and some students volunteered to show their demos today.

I have asked students to take on this task for a variety of reasons. First, one of my failings as a teacher is that I am terrible at demonstrations! Second, and more importantly, students both enjoy the process of finding and prepping a demo but also seem to internalize many of the fundamental concepts of charges while doing so. As a related note, the sense of fun and playfulness that accompanies this exercise goes a long way toward creating student ownership of the classroom.

Today's demonstration features a soap bubble within a soap bubble. A charged balloon can be used to move the outer bubble around the table while the inner bubble remains unaffected. This demonstration, like many others in this series, helps students see the impact of charged particles. Our computations are always centered upon the interaction of just a few charged particles but isolating small numbers of charged particles is impossible in our setting. When we create situations where large numbers of charges are assembled, students can more easily see their interactions and, I believe, gain greater comfort with the force and energy calculations involving small numbers of charges. Though this particular demo is tricky - the creation of a bubble inside a bubble can be vexing - the students show some tenacity and pull it off nicely.

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#### Creating Idea Webs

*25 min*

After the demonstration, I ask students to create an Inspiration-web for Electrostatics. "Inspiration" is a software program for which our school has purchased a site license. It enables students to create a visual web of ideas from a brainstorming session. After creating an initial web, students can alter the color of segments and move elements around on the screen for a better sense of the way their ideas are organized. I am very interested in capturing, qualitatively, their understanding of this topic at the end of our instructional sequence and wish to compare their webs now with ones that were created at the beginning of the unit.

Students work at department-provided computers which have been previously loaded with Inspiration. Because of the limited number of machines, students work in pairs. Though they know that this work is not being graded, students are happy to create the webs and share their best thoughts about the topic. The task is not onerous, class time is being provided, the rapid-fire nature of the web creations is intriguing, and the ability to manipulate one's finished web are all aspects that increase the level of engagement, despite the fact that there will be no grade assigned.

After creating a web for the now-familiar topic of electrostatics, I ask students to create a second web for the word "Electronics." This topic is much less familiar to them and, naturally their webs will be sparser. But I collect their initial thoughts before formally beginning our unit. Students either print both webs or electronically submit them to me for formative assessment.

Here's a sample student web.

#### Resources

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In anticipation of a summative quiz next week, I offer my students this "mock quiz." It comprises questions that I think students should understand.

I ask students to take this under "quiz-like" conditions. Therefore, they work solo and should not, at least at the start, consult their notes. As this is a form of self-assessment, I feel like it is important for students to recognize the topics where their understanding is weak; reliance upon notes can mask that. On the other hand, sitting and struggling for 20-30 minutes today would be pointless, so I allow students to consult notes after a 15-minute window has passed. I do not collect this but, rather, encourage students to continue to use it as the best possible review strategy for next week's actual quiz.

Between today's lesson and the quiz next week, students can consult the solutions to the mock quiz which are posted on-line. Students are offered transparency (no surprises about quiz content), support (solutions on-line), and opportunity (time) to prepare. These feel like essential elements of a fair test and they are provided in a process where students can practice self-direction and self-assessment.

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- LESSON 1: Introduction to Electrostatics
- LESSON 2: Introduction to Forces and Work
- LESSON 3: Forces and Work Revisited
- LESSON 4: Enhancing Our Model of Work
- LESSON 5: Enhancing Our Model of Work - Revisited
- LESSON 6: Investigating Work and Forces - Day 1
- LESSON 7: Investigating Work and Forces - Day 2
- LESSON 8: Multiple Charges, Multiple Forces
- LESSON 9: Self-Directed Day
- LESSON 10: Charges and Forces at Right Angles
- LESSON 11: Redefining Work - An Introduction
- LESSON 12: Redefining Work - Day 2
- LESSON 13: Electric Potential Energy - Introduction
- LESSON 14: Electric Potential Energy - Day 2
- LESSON 15: Reflection on Electrostatics