Saturday, January 23, 2016

Logic Gates: Boolean algebra meets simple circuits

Back in the late 1980s and early 1990s, I was slowly but surely amassing the empire of equipment I now leverage in my physics lab. Back then I felt a freedom to develop lessons and labs that were useful in teaching physics principles and applications. There were no content standards looming over my head. No Common Core State Standards to shoehorn my lessons into. No multicolored, multilayered, NGSS alignment demands.

Evidently, none of my students learned a thing about physics or science back then. Such a pity.

Once my lab was geared up for simple circuit labs with a full complement of batteries, bulbs, switches, and wires, I allowed my serendipity to wander. (I tended to do this whenever I got new apparatus.) I knew the standard things that could be done. But what else?

One such meander led me to develop "Logic Gates". Instead of connecting resistors or bulbs in series or parallel, how about connecting switches in series or parallel. The results were simple circuit representations of Boolean logic: realia that could be used to fill truth tables! (I studied Boolean logic and truth tables in high school math. Apparently that's no longer done.)

Since the very concept of Boolean logic was foreign to my students, I created a prelab exercise to bring them up to speed before launching them into the activity. It's the classic "Besse can get to her pasture if Gates A AND B are open…" story, with all requisite variations. Since a bright student named Haleh made a point to tell me how useful the prelab was, I named the worksheet "Haleh Cow!". It's what I do.

Once students have the hang of Boolean algebra (if-then, and, or), it's time to break out the circuit gadgetry. In the old days, we powered the circuits with batteries. Nowadays, we use Genecons (which are much more forgiving for the NOT gates).

NGSS doesn't call much for anything related to electric circuits. So this activity is relegated for use with AP Physics 2 students, only. In any case, here's the lab.

It should be noted (especially in light of Bree's insightful post) that this activity got pushed into dormancy when standardized testing was phased in. With AP1 and AP2, I have been able to dust off a few gems from bygone years. If I could reanimate my revisions of Dewey Dykstra's implementation of Fred Goldberg's optics learning research (from back before PER was a thing), that'd be great! 

1 comment:

kyle said...

I LOVE this! I am totally going to use this this week. I am trying to teach logic right now with transistors and 555 timers in my physics 2 class and have been at a loss since our books don't really go into it at all. Thank you for sharing this!