Day 36: Reteaching Electric Potential


YESTERDAY: The intro lesson on electric potential difference was a flop. I had students solve problems about moving particles in constant electric field for varying amounts of charge:

2015 APC Efields

2015 APC Efields (2)

Then I asked them to generalize for any amount of charge q:

2015 APC Efields (1)

and then tried to make the connection to this new quantity called electric potential difference. Big flop. It felt abstract and contrived.

AFTER CLASS: I dug into Knight’s books and Etkina’s book to see how they approached it. Both of them did potential first (not potential difference), and took a fields approach to potential. They drew parallels between the relationship between electric force/electric field and electric potential energy/electric potential. This seemed like the most natural approach for our class, since we’ve been rocking electric fields for weeks and just finished up electric potential energy.


TODAY IN CLASS: We talked about Knight’s conceptualization:



and Etkina’s (she goes a step further and literally calls electric potential the V-field):



And if electric potential can really be treated like a field, we need a way to visualize it. But it’s not a vector, so we can’t visualize it like we do electric fields. I talked about the concept of a scalar field (or “heat map”) and showed this map of air pressure in Europe:


We discussed what the colors meant and what the lines meant. (They all had Earth Science previously, so this wasn’t entirely new to them.) Then we looked at the PhET’s Charges and Fields simulation:


I think visualizing the V-field was really key, rather than taking the “work-based” approach I had done yesterday. The picture at the beginning of this post is a summary sheet of the discussion.



About Frank Noschese

HS Physics Teacher constantly questioning my teaching.

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