Unit 4: Magnetix

Finally, the part I was most looking forward to. Playing with magnets. How could I have been so simple minded? We weren't going to just play...we were going to dig deep down into the pit of confusion and chaos, of right hand rules and mysteriously moving wires. Of magnetic field lines coming out or going in- who knew which?

Better fuel up....

The morning selection...

Ok, let's get to work. We started with compasses and flowing charge in a wire.

field around a wire

We mapped the direction of the field and decided that the field swirls CCW when the current is up and CW when the current is down.

looks like we are learning to tell time!

Vectors

Then we were able to take some measurements of the strength of the field. We changed the current and measured how the compass was deflected, then we changed the distance. We "logicked" through the kind of curves they were- distance looked linear but couldn't be, because it would cross the axis and change direction! So it turned out to be inverse. Current looked linear.

Next we got magnets to play with - a bar magnet and face magnets. We mapped the field around these magnets and then had an interesting and protracted (always!) discussion about which way the earth's magnetic field goes. Now I thought I had some background info on this because I teach astronomy and I show a video called "Magnetic Storm" about how the earth's magnetic field is changing, but it turns out I really wasn't clear on it even after watching that video eleventy umpteen times. So the field goes OUT of the north pole and INTO the south pole. By convention. So the end of a compass is "north seeking." But..."it's been known for many years"...that the magnetic poles of the earth do switch and it is actually long overdue for such a switch.

We delved into some worksheets to help figure out directions of currents field and forces, and through much trial and error, we did come up with a right hand rule. Colleen actually thought through it as her table mates seeded her way and came up with the hand rule herself! Bravo!

so...we could actually use our right hands to help remember...

Give her a hand!

B, F and I are all at right angles to each other, which is what made visualizing it a three dimensional abstract jungle gym nightmare of mental contortions.

So there's a rule for current in a wire: thumb in direction of current and fingers curl in the direction of the magnetic field. Easy peasy. But for force- the fingers go in the direction of the B field, the thumb in the direction of current, and your palm OF YOUR RIGHT HAND (I used my left once and then had to face palm myself with it...) is the direction of the force.

3-D Craz- E

bending our brains...

We "learned" the notation for in and out of the page, so we could better keep track of which way fields were tending. After a lot of fiddling with magnets and drawing fields, we had a recap from Laura about all the things we'd discovered. I think this is important- because I had been getting lost in activity after activity. It's good to pause and take inventory of what you've learned and what is still out there to be explored.
So:
1. We mapped the mag. field and concluded we could use the RHR to show direction of field.
2. Mag. field came from charge flow.
3. Mag field comes out of north (convention)
4. Mag field changes in different contexts
5. inverse relationship between B and d
6. B is prop. to current and inversely prop. to distance

Next came the coils. The Copper coils. And bar magnets. And meters to measure any nonsense going on.

copper coil

Here's what we think:

field around coil

Things get pretty tricky pretty quickly now. We were finishing up in the final days of the workshop. We'd been at it over two weeks- we'd had no break from teaching, laundry was piling up, families needed attention, etc, and things at the workshop got tougher. But it would have to. How else could you understand how a moving charge could create a magnetic field, or that moving a magnet through a coil could cause a current. It's tricky stuff. But very cool. And very useful.

put the magnet in the hole...pull it out...

The next lab was a demo lab because the equipment was expensive, but we could actually "weigh" the force with  a charge balance. We changed the magnet strength, the thickness of the wire, and the length of the wire. After we graphed our data we saw linear relationships for all- concluding that
F = IBl.
We had more debriefing  from Don and he made a connection with springs and how they add. This is where we codified our information about resistors, capacitors, and how we treat them in series versus parallel. We talked more about the reading we had done and he made some connections with the terminology- "surface charge" and "steady state" and "quasi-steady state." It made much more sense now that we had so much experience and context in which to put it.

One of the final activities we did was a lab I called The Mortal Coil. We shoved the magnet in and out of the coil, and figured out which way the current was going by using all our appendages, right hands, left brains, and abstract thought...and we ended up with the old magnet through a copper tube trick which I've seen many a time, but Don went through the explanation of how it could be that dropping a magnet through a copper tube could produce a field opposite in direction to the magnetic field of the magnet- thus slowing down its progress and acting against gravity.

This explains it all! 

Unfortunately, it wasn't just 3:59pm on a friday when the learnin' gets tough, it was 3:59 on a friday of the last day of a three week intensive study of E and M in the Modeling framework.
That's tough times five. 

But I grasped just enough of it to make me want to think more and read more and think more. I know there is more because I took the E and M semester of physics at HFCC when I was getting my teaching degree 8+ years ago. And I remember words like flux and faradays and webers and rotating loops of wire.

Now, I'm almost 100% sure I won't get to this material in my high school classes. But how much richer is life when you really get a feel for how things work? And how much richer is learning when you get the chance to construct meaning and experiences that lead you to a deeper understanding.

So now the workshop is over, but I have so much more work to do. Planning and plotting and getting things ready and thinking about how I will proceed. Luckily i won't be alone- I met and worked with a cohort of very cool and very smart people who I will use as resources.

Physics discussions continue at a more informal setting...

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.

Oh, a series circuit!

Meanwhile, how thrilled was I when the toy I ordered showed up. It doesn't take much to relieve the stress of cognitive dissonance!

Sharky!

We all worked really hard! 

editing our ideas

Next and last unit, Magnetism. Sounds fun, but is it really? ...

Unit 2: We've got Potential

Unit 1 ended with drawing electric fields around charges. We reasoned through the rules of drawing them. I almost said "we learned," but we had gone through a lengthy discussion of gravitational fields, so by the time we got to charges, it was easy to come up with the "rules" of drawing field lines.
1. They ALWAYS point in the direction of force arrows.
2. The closer the field lines, the stronger the field.

Now, it's amusing that we came up with rules at all, because in hind-sight we often ignored that second rule in our own quest for representations that made sense to us. Sometime we drew them longer rather than denser, but the first rule did seem to hold for us!

At this point the idea of critical competitors came up- ideas that are similar but also different enough to make you wonder. We had been comparing the gravitational field of the earth to an electric field, and though there are many similarities, the differences began to emerge. And we hearkened back to other ideas on energy and magnets. This was a good review of energy and also a good connection to gravitational energy and electrical energy. We were reaching for this idea of Potential. Not potential energy, but the potential, which turns out to be a rather esoteric idea for gravity but much more useful for electricity. If you divide the mass out of gravitational potential energy, you get potential. Same goes if you divide the charge out of electrical potential energy. You are left with a potential at some point away from a charge. To further introduce this idea we stood on table and chairs to  make a model of a field with potential.

Energy levels! (I'm on the ground floor:)

Those of us on the table had more gravitational potential, etc. We then were able to make a connection between gravitation and electricity by drawing "topo" maps.

Just like a hiking map!

Once this connection was made, we had a way to visualize potential. We were ready for what I consider a watershed lab that served not only to help shape our ideas of potential, field and forces, but for the rest of the course I do believe it influenced how we thought about electric issues. Really, this lab was referred to for the rest of our time together.

It really was quite simple in execution. There were two bars wrapped in aluminum foil in a lasagna pyrex pan partially filled with water.  They were connected to a power source so that they had opposite net charge on them. We used the probes from an electric field detector (a voltmeter) to plot how the electric potential changed between them. We drew it on some quad ruled paper and we had a map of the electric potential around two lines of charge. Then we used Plot.ly to see a three dimensional representation of the field between the two lines of charge.

plot.ly'd

That was pretty cool! And we drew it on our whiteboards!

It's like a giant slide.

Colors help.

another depiction

I've just realized that I've been using the pronoun "we" in describing activities. Is it because I felt like it was always a group project? That we were all thinking together? I don't think I felt that way all the time. I personally am more of a loner. I also take time forming a big picture- making the connections I need to understand the big ideas. I'm not much for getting stuck in details, and I got impatient sometimes when folks hashed over what I considered trivial matters,which may or may not have been. I think most folks were struggling with their desire to tell. We changed groups often, so we did get to work with lots of different people. I guess what I'm trying to say is that I learned a lot about myself and other teachers, and a lot about how students may feel when they are doing these activities and interacting with each other. I do have a lot of food for thought about how I want to proceed with Modeling. Don gave us a lead on a great book called Mindset which I ordered, and in talking with others who have read it, it sounds like it could change my teaching. It's going to be my next read.

Back in the world of Physics, our lab led to much exploration of this idea of potential and how to imagine it, and how to depict it. I have many drawings in my notebook, and I even have a little cry-face drawn with the caption "wkst 3 is super confusing: using grav. equipotential to explain energy and potential."I must have hit some cognitive dissonance. Again.

But we soldiered on, through mini pep-talks about students having to get used to teachers not giving them an answer...whew that's a tough one. Especially for my AP students! I will be strong. I will let things hang in the air. I will let there be awkward silence. I will give pep talks about how important it is to hit upon ideas in your own context rather than being told by someone in their context.

There was a long discussion about the strength of the filed between two lines of charges connected to a potential difference (battery or other device) Laura, with the patience of a saint, took us through a quagmire of discussion about inverse square laws and how they may or may not apply to this situation. Turns out it didn't. Turns out that the electric filed remains constant no matter how far away the plates are from each other. Do they really? Yes they do. It was difficult to swallow until Laura played with geometry and math and we walked through the logic of it. Tough day!

Real learning: a permanent change in cognitive structures and procedures.

Next came the Genecon lab- fun city!

Geneconning

We explored energy transfer from the capacitor to the genecon by counting how many turns the handle made when connected to the "energized" capacitor. With this lab we were able to make some connections between energy and potential difference. It appeared to be a squared relationship, which our data supported. So we continued exploration with capacitors on the Phet lab. We learned that the slope of our graphs told us about the characteristics of the capacitor, and we refined our relationship between energy, potential difference and charge.

Discussing our board!

While we were doing these ongoing explorations, we constantly edited and morphed our representations so that they were understandable. I was often reminded of how much of a stickler I have been as a teacher about using correct units and labeling graphs, and having a consistent representation, regardless of any understanding about these tools. I am definitely of a different mind now! Work towards the understanding, and the details will follow.

I am going to teach for understanding, not for "the right answers!" We had an interesting discussion about how we were in an emotional and educational quandary; trying to understand with new and unknown representations while engaging this new material, even if it isn't totally new to us. Plus we all have "learning baggage" that we bring to the circle. I was very aware of my learning baggage, and my interaction baggage! So I can imagine how my students must feel. Discussions have been very eye and heart opening!

Meanwhile, the whiteboards are getting better- I think Don's example of well-drawn lab set ups and his perfect circles have inspires us to do better on our own whiteboards!

Capacitors

and more...

Capacitors are energy storing devices. I wrote that in my notes. But how much fun we had discharging them and finding out what happened to charge flow. We learned how the area and the distance between the plates changed the energy output. We did this with real capacitors, and also with a simulation which really helped see what was going on my manipulating the factors like area and separation. We found that capacitance was directly related to Area and inversely related to distance, as one might expect. But it was fun to see it.

Phet simulation

Cap happy.

Next chapter: on to Circuits.

Unit 1: Charge it.

First week: we jumped into Electricity by asking questions about charge. Why does a balloon stick to the ceiling after being rubbed on hair? It's not enough to say "static" or "electricity". What does that mean? Why does the balloon stick to the ceiling. We've all done it, but who among us can explain it? A roomful of dedicated physics teachers?

Nay! Not in "student" mode. Student mode is when grown, degreed adults have to "forget" what they thought they knew and act as if they were learning the subject matter for the first time. It's surprisingly easy to do when you throw yourself into it, because it turns out that grown adults, even those trained in physics, have a relatively shallow understanding of physics. It's not because we're sleeping on the job. It's more because nature is a sly fox, and is a lot deeper and richly layered than we often have time or energy to explore. And explaining it meaningfully is challenging.

We have the language to do it, but sometimes the language bars us from true understanding. That's why in Modeling, we save the name for last.

And that's why it's surprisingly easy to feign ignorance when your jargon is taken away. Imagine trying to talk to someone about being a lawyer if you can't use the words "prosecute" or "defendant" or "law!"

So we bandied about terms like positive and negative, like and unlike, and attributed it to Ben Franklin, who made positive plus and negative minus, and went right into a lab centered around sticky cellophane tape.

The sticky tape lab is elegant when it works, but very difficult to pull off. That's a pretty funny pun when you know something about the lab. We started by putting three pieces of tape down with little tabs at the ends. We ripped the top one off the middle one, then pulled up the middle one, and ended up with two lengths of tape that either repel or attract, depending on their mood. It really isn't mood dependent, but it wasn't always a sure thing that they would repel in a consistent matter, which is what this lab intends. I've tried it with students before and the variation of results is maddening. However, after going through it again, I think it's very useful to push through the variations and guide the students through it. We also threw a balloon into the mix for more fun and variation in part 2 of the lab.

Through much exploration, we came to some agreement in discussion that we can talk about charge as a thing, but not necessarily have a definition for it. That will be a common theme in this landscape. Our goal is not to be "right" but to understand as well as we can what is going on.

Fun went on when our beloved leaders handed out the Fun Fly sticks. Fun is in the name, and with good reason. Little sculpted bits of mylar performed acrobatics when brought near a positive charge producing wand. How did we know it was positive? We positively inferred it!

The silly fun sticks served a purpose in letting us lighten up in the darkness of confusion and uncertainty. It's not trivial to be put in a position of uncertainly about what you thought you knew. About what you do as a career. About what you teach other, impressionable, trusting minds!

Styro towers

Then came the pie plates. The cheap, dollar-store pie plates. With styrofoam cups glued on as non-conducting handles, of course! Easy to charge, easy to use!

touching pie plates!

apparently it's a happy event!

Ba ba bwat?

So we played with the plates and pink foam and learned a few things about charge transfer. As we pieced our ideas together, we gathered for white boarding sessions. Whiteboards are the main tool of Modelers. Discussion is the method of transmitting ideas and the whiteboards aid in that goal.

However, sitting around in large groups talking is an introvert nightmare. And I'm an introvert.
But you can't really solve problems and learn without discussion, so whiteboarding it is. And it's not so bad~ group dynamics can be very enlightening!

Delicate pith action

Through questioning, not "teaching" as we teachers are wont to do, we are able to come to some conclusions, or at least reach a point where we can move on, even with questions that still remain hanging. It's a place of vulnerability, but true learning requires vulnerability.

At some point the VanderGraaff generator was hauled out for some real old fashioned fun. I think we were all feeling pretty OK with the material at that point. Fools!

Delicate pith action

We were just wading in. Thence the pith ball lab, where we really examined the separation of charges and the electron transfer model began to grow feet in our minds. It was a challenging lab, but by the end we were able to confidently say that opposite or neutral charges attract, and the only like charges repel. Elementary, dear Watson? Perhaps, but very powerful for determining charge, since only like charges repel.

Need slo-mo camera action

The pith ball lab used a lot of math and graphing skills, and some trig functions. But we were able to divine a relationship from it, and it included an inverse squared relationship. Spoiler alert- that darn relationship shows up in places where it shouldn't in future labs! 

I must take some time to mention that in between this action packed agenda, we had time for mini pep-talks. Discussion is difficult. Slogging through the minutia of foggy understanding is exhausting. But why are we doing it? It would be easy to tell. Teachers are the know-it-alls of society. We love to tell things. To transmit what we know by talking. But the reason we are spending the first three weeks of our precious summer rejuve time at this course is that we KNOW without equivocation that telling doesn't equal learning. And no one likes a know-it-all. 

With that said, we did get some direct instruction on the similarities between gravitational fields and electric fields, and many connections were made. But it was always done with an eye toward understanding and building on what we had done and seen previously.

So on to Unit 2 to make sense of Electric Potential!