Desmos Activity: Electric Field Due to Point Charges

Two of my main goals when teaching students about electric fields are getting them to understand superposition and vector addition.  I usually do this by having them sketch several examples, but it is difficult for me to provide good feedback.  So I decided to create my own Desmos activity: Electric Field Due to Point Charges.  The basic idea is that there is a green region, and you have to maneuver charges until the electric field vector falls entirely within that region.  (By the way, Desmos is quickly becoming one of my favorite teaching tools.  The activity builder allows you to create scaffolded activities that are still interactive.)

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Screenshot from Desmos activity: Electric Field Due to Point Charges

I tried to use design elements to make the activity feel as natural as possible.  For example, positive charges are red and negative charges are blue.  Each type of charge produces an electric field of its corresponding color, but the combination of a red charge and a blue charge will produce a purple electric field.  The process of design is still pretty new to me, though, so if you have any suggestions please let me know in the comments.


Curricular Structure

A typical week in my classroom used to look like this:

Stuff More Stuff

I have always been slightly bothered by this approach, though, because it makes it difficult for the students to determine what is important and what is not. All of the material more or less blends together in one constant stream.

This year, I am experimenting by adding a regularly structure to my weekly plan. It looks something like this:

weekly structure

The first day of each week is about assessment, lab skills, and epistemology. We start with a quiz based off of the previous week’s material. It lasts about 15 minutes, then we spend a little time going over the answers. Next, we do a lab that typically starts with a single investigative question, like “What is the relationship between the mass on the end of a spring and the period with which the spring oscillates?” The students determine the procedure, carry out the experiment, then create a linearized plot of the data. In the end, they will have an equation for the relationship in question. The goal of this lab activity is to introduce the topic of the week and to show the students that physics knowledge ultimately comes from experiment, not an authority figure.

On the second day of class, we flesh out the topic, and students work on establishing a conceptual understanding of the material. I start by lecturing for about half an hour, using the equation that the students’ determined in lab as a jumping-off point. For the next hour, students break into groups and practice qualitative questions (we use Randall Knight’s Student Workbook). The questions typically involving ranking tasks, proportional reasoning, etc. Before the end of class, we reconvene as a group, and individual groups show their answers to one of the questions on a whiteboard.

On the third day of class, we add a level of complexity to the material, and students work on honing their quantitative problem-solving skills. I start by answering student questions and filling in details of the content that I didn’t have time to fit in on the previous class day. The next hour or so is fairly open-ended, but the focus is on quantitative problems. Sometimes these are typical end-of-the-chapter problems, and sometimes they are more interesting challenges.

There is a very clear delineation between new content, practice, and lab work, and I think that helps the students “chunk” what they learn in class. I also like that the structure helps me focus my content delivery. Limiting my lecture time helps me focus on what is really important. This obviously requires sacrificing breadth for depth, but that is a sacrifice that I am willing to make.

I am pretty happy with how this class structure has affected my classes so far. It is not without its faults, and I have some ideas for improvements, but I will save that for a future post. Have any of you tried implementing a regular structure like this? Are there things that you would do differently? Let me know in the comments.