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.

Sharing Whiteboard Work with Mathematica and Instagram

I love using portable whiteboards for group work in class, but the ephemeral nature of the students’ work means that students will not have a written record to refer back to later.  One solution I tried last semester was to take pictures of the whiteboards with my phone.  Then after class I would upload the pictures onto Google Docs that contained the corresponding questions.  That was workable but a little less efficient than I would have liked.  

This semester I am preparing my notes and in-class activities on Mathematica slideshow presentations.  In trying to figure out efficient ways to upload pictures to the documents, I discovered that Mathematica integrates with Instagram.  With just a couple lines of code I can import any image I want.  So here is the plan: at each point in the presentation where I want to insert pictures of student work, I write a couple lines of code that search Instagram for photos with a particular tag (a tag that I can remember and that is unlikely to be used by anyone else).  Whenever I take a  picture of a whiteboard, then, all I have to do is put that particular tag as a comment for the picture.  Then I hit Shift+Enter on Mathematica and the pictures instantly appear!    

Thoughts?  Is there a better/easier way to do it that I am missing?