Far Out Physics: Unit 3: Circuit City

What's happening in the wire? It's just a wire!

Ignoring wires is the norm in entry level physics, like ignoring air resistance, friction and even gravity at times! It complicates things. But it turns out that there is something going on in the wires. And we found out what it was! Charges separate and gather along the wire under the influence of an electric field. Of course they do, but we explored that fully so that we could decided when to ignore it and when to pay attention to it.

evidence!

The reading we were given in the beginning of the course was a rather deep explanation of what happens when charges move under the influence of an electric field. We all were duly puzzled after the reading, but a piece or two of the puzzle fit better with our exploration of the wires. Including the wire potential differences in our calculations also made our data fit better with our readings from the multimeter. However, when it came to representing what was happening, we had more deep and lengthy discussions. How do you show a potential difference in the wires, and across bulbs with different filaments? Tricky business. I must admit, I remember feeling very foggy wading through this landscape. Part of the problem was that I had a hard time interacting with my lab mates, who seemed to be on the same wavelength, and I felt like I was on a much longer, slower wave, even though I know all waves travel at the same speed! (or do they?) So I had to try to figure things out at my own pace, and yet participate in the group. This was my educational baggage.

I reflected on the different personality types and how they might interact in a group setting. I think I will have much more compassion and be more aware of how students might get emotionally shut down. It's nearly impossible to learn when you are shut down. Being sensitive to this should help me keep the kids learning as much as possible.

Physics-wise, we went back to the lab to discover more about wires and bulbs and circuits. We used a short bulb with a thick filament, and a long bulb with a thin filament. These differences, and their subsequent different brightnesses, led us into the realm of really "seeing" into the wires and the bulbs. Is the charge still moving though the bulb doesn't light? Spoiler alert- later on we see evidence that it is still moving. We "spiraled back" to the question, which is how we are able to leave loose ends and let the students have dangling questions. I worry though that I will forget to "spiral back" on some things and they will be hanging out there forever! or until the student asks, I suppose...

Anyway, we did the best we could representing what we thought was going on. That's a pretty wishy-washy sentence!

Hmm...

We did have a useful way of imagining the battery as a conveyor belt, moving charge from one side to the other- or up the potential hill. That's what that little blue thing in the battery box is. Once again, after protracted discussion, we decided that we needed to explore more before attempting to create our model.

Our next step was to notice the difference in the bulbs when we setup circuits in two distinct ways. However we did not know the words for these ways yet, though I did hear the mysterious words "series" and "parallel" from various corners of the room. As I mentioned early on, it's easier to talk about physics when you have the words, but it doesn't lead to any understanding of the concept behind the words. So for our purposes as teachers teaching for understanding, it's better to give the words out later, like a stingy vocabulary-miser.

Whatchamacallits!

So we made many measurements of charge flow in two different kinds of circuits. We added batteries to the circuits to determine what happened to the charge flow. Through our data analysis we were able to draw some conclusions about the relationship between potential difference and charge flow- as V goes up, I goes up. Ohm's Law, we found out! We learned the symbols through direct instruction, but only after we had gotten to the point where we needed a name for them. And not a moment before! We also found that the area under the graphs we drew of I vs. V showed us the rate of energy consumed, otherwise known as power.

This is somewhat familiar territory now, although approached from a very different direction than I have ever taken. We had a question about if light bulbs are ohmic, meaning do they follow Ohm law linearly. It was a natural question coming from our data, but I never would have thought of it before with my surface understanding of light bulbs. However, it remained a mystery for a time.

Our final exploration of circuits was about finding out what happens to resistance in the two types of circuits, and by carefully measuring current and adding resistors, we found that in a series circuit, the more resistance, the less current- an inverse relationship. But with the "other" circuit (I don't believe parallel ever was mentioned) current actually increased in a linear fashion when we added resistance. Armed with this information we were able to go on to the deployments and work through using these ideas.