Navigate back to the activity.

Comment from S. Pollock (CU Boulder, visiting OSU and teaching Paradigm “Vector Fields), Nov 2009:

We started this activity in the last 20 minutes of class (Lect12). My students struggled massively, this activity was just too vague and difficult for them to make progress. I felt this may need more scaffolding. Students couldn't visualize a “general E field” near a sheet of charge (they wanted it to point outwards), and they couldn't bring themselves to start constructing Gaussian surfaces and evaluating Gauss' law on that surface with no formula (name) for the E field to start with. At the end of about 10 minutes I tried setting it up by labeling E(above) and E(below), and encouraging them to pick a tiny surface and start evaluating, but they were still reluctant to tackle this.

I returned to the activity after a long break (T-giving), and spent another 10 minutes of class time on it, beginning with a little blackboard sketch labeling the fields and trying to be a little clearer about what their task was (looking for a formula for the discontinuity (or argument of continuity) of components (perp, and parallel, to the sheet of charge). There was a little more progress this time, and after 10 minutes of group work, I called on groups to talk through their arguments. This worked well, we pieced together much of the story: about the continuity of E(parallel) from “an Amperian-like loop”, and the discontinuity of E(perp) from a Gaussian surface. What was missing was the story of the “other legs” (or sides), which you must make go away by careful choice of SIZE/shape of the box or loop. I pointed out several examples they know (infinite sheet, or cylinder) and invoked superposition to talk about how you cannot assume E points in any particular direction, ONLY that you can conclude E_perp jumps across the sheet.

At this point, I returned them to groups to do the B-discontinuity story (written up separately).