Sunday, April 22, 2018

Tuesday, April 17, 2018

How to teach a class you've never taught before

Short answer: work hard.

Oh you wanted specifics? Keep reading.

One of the intricacies of education is that we can do the same thing year after year but nothing is the same or we can teach a completely different class and everything is still the same. Here are two examples:

I taught Physics every year for ten years. In that time period there have been new national and state standards implemented, two major bell schedule adjustments changing the number of minutes per day and week, furlough days have come and gone, new rallies and school traditions take instructional time, I have changed rooms four times, decided to forgo homework and gotten a new textbook twice. While I have taught "Physics" for ten years the class I would teach now is not the same as when I started.

I have also taught Conceptual Physics seven times in ten years. Several times there was a year in between in which I did not teach it. The population changed from freshmen only to freshmen and English Language Learners to open to all students to freshmen and special education only. The book has not changed but I have also had the same schedule and calendar changes I experienced for Physics. Because the class was meant to sere students that need additional support many of the pedagogical approaches and project based learning remains the same.

It can be hard to teach a course you have taught before with textbook or schedule or population or calendar changes. And then you may have to teach something completely different. Physics teachers often have to teach non-Physics courses because of traditionally lower enrollment in Physics classes compared to say Chemistry. In some schools they are the only Physics teacher and thus teach multiple levels. We tend to have more preps (different classes to teach) and change them up more often than other science disciplines. In your career you will probably at least once have to teach a brand-new-to-you course that makes you feel like a new teacher all over again. That's what happened to me this year with AP Physics C.

While I would love to say I met the challenge gracefully with my years of experience that was not always the case. Sometimes the workload crushed me. It definitely left my family neglected, our house in disorder and our lives chaotic. But as the end of the year approached I found that it got easier, not because the curriculum did but because I had developed a process. I found, through absolute trial and error, what helped me and what did not. I realized I went through the same steps in the same order at the start of each unit and it started to get (incrementally) easier.

And thus I decided to share, not because it is innovative or particularly amazing but because it could be helpful. I know someone out there, experienced or not, will be told in the coming weeks that they will be teaching (gulp) some class brand-new to them. It is daunting, makes you question whatever skills you thought you had and the workload downright sucks. So if some of this process helps you, great. If not, hopefully it helps lead you to your own.

Start with what you are given:
If you are inheriting the course from someone else you may find that you have also inherited a few filing cabinets worth of material. Or binders. Or shelves and shelves of "teacher resources." It is time consuming but worth it to go through this materials and do a first sort of what is and is not useful. Ditch the floppy disc versions of your textbook's teacher materials; ditch multiple copies of supplemental materials (unless there is more than one teacher). Check with your district about district copies of these resources, they may wish to consolidate extras in their warehouse for potential future use. You don't have to read every piece of paper left for you in a file cabinet now, you don't have to decide to adopt everything they left for you but you may want to keep it to give yourself the option.

As I moved into my new room this year there were eight total file cabinet drawers left for me for Physics and AP Physics. In my first sort I kept one copy of everything. I wanted to be able to read the labs he wrote but figured even if I decided to do the same ones I would probably be retyping it. I wanted to be able to see what his tests looked like, but knew I didn't need a class set. I kept a copy of his handwritten lecture notes so I could see how he implemented material, even though I planned to make powerpoints. I kept the manila folders, overheads and single sided paper to reuse as scrap paper. In the end, I filled four full size recycling bins with the paper I discarded, that was just the double-sided stuff. What I kept fit in two 4" binders in page protectors. I separated the stuff by unit, or at least by what I thought was by unit at the time. I was left with no digital files, except for uneditable pdfs I was able to download from  his website before the district took it down.

As the year has progressed I started every unit going through what I was left. I looked over and digitized the lecture notes (you can copy it into a tablet or just scan it) to see how the material was presented before. If there was a worksheet that I wanted to use I would retype it as it was at first. I then did the worksheet myself and edited it how I wanted to for my own kids. Basically I took a look at what was done before as a guide, not to follow exactly but just for comparison. It provided a place to start, so I didn't have to start from scratch. There were plenty of worksheets, labs, etc. that I took this second look to and tossed aside. If you are lucky enough to start a new-to-you course that someone else teaches, start with everything they have. You can change things but it is invaluable to see how someone else teaches it, for better or worse.

Textbook resources:
While you may or may not use your textbook, electronic or print, your district has probably adopted one. Looking through it can be helpful if you have to learn or relearn material. I would read and take notes on each chapter, so that I could experience how the material was introduced just like my kids would. Most publishers have digital teacher resources now, either for download or on their website. My publisher has answer keys, lecture powerpoints, test banks, image galleries, simulations and more. So as to not re-invent the wheel, for each unit I started my lecture powerpoints using the textbook ones as a base. As the  year progressed less and less of the original remained but it saved me time when I had so little. While using pre-made resources is not ideal, you should personalize your curriculum for yourself and your students, it is not the worst starting place. In later years of teaching the course you will probably use your own materials more and more.

Find reliable resources:
No class should be taught by textbook alone. Finding a few trusted and reliable resources for your class is important. This may be a professional networking site or another teacher's website or even social media. I found helpful materials on a wiki page, PrettyGoodPhysics, that will sadly need to relocate. There were a few YouTube Channels that provided consistently good tutorials by subject for myself and my students. Sometimes it would be for a different course (AP Physics 1, 2 or Honors Physics) but good video lessons are good video lessons regardless. I recommend Flipping Physics, Dan Fullerton's APlusPhysics, Mrs. Twu's video tutorials and  AKLectures Physics series. If I needed to review a topic, or more importantly to learn what to emphasize for my students, it was very helpful watching other teachers teach it.

Social media turned out to be one of my greatest resources this year. I was able to find other physics teachers I did not know on Twitter and could follow or use hashtags like #APphysicsC to find resources by course. I was able to share data that didn't make sense and tag the equipment manufacturer who would often very quickly respond with suggestions. I once tagged @VernierST in the middle of a class period about weird looking data and got a response before my students left that period. They would continue to work with me for days as I tried to troubleshoot. Other teachers could jump on the thread and make suggestions or share sample data in the worst case scenario that nothing worked. I could share pictures of student work that made me scratch my head, asking more experienced teachers how I could prevent such incorrect problem solving in the future. As other teachers shared pictures of labs or demos they were doing I could save the picture for future use. I've even reached out to individuals to ask for their lab write-ups, ask follow-up questions or for advice. And they respond! Teachers usually like to help other teachers and many have been amazingly generous, sending me full curriculum guides, sample lecture notes, etc.

And perhaps most importantly, they don't judge much. On Twitter and on the College Board AP Physics C list serve I have posted problems that I cannot solve, or conceptual issues I still have that are preventing me from teaching it to my students. More experienced teachers have been able to respond with suggestions, solutions or alternate ways of approaching the problem. Everyone was patient as I usually started out my requests with "Since it's my first year teaching #APphysicsC..." And since I was putting that question out to anyone who could answer, people that could would and I would crowdsource some great solutions.

I also collected textbooks. Luckily we just adopted new AP textbooks so we had a textbooks from all the big publishers who had sent materials during the adoption process. I currently have six textbooks on my table, and I would often flip through all of them. For each chapter I would look through them to see if the example problems were different, how the material was grouped or arranged and to see what was emphasized. If my adopted textbook emphasized a type of problem that didn't appear in the other textbooks it helped confirm what was outside of the scope of the class.

Ask for help:
You know you should but it may still be difficult to admit that you don't know everything (yet) about your new course and you need help. Sometimes it was about the scope of the course, as my textbook includes a lot more than what is included on the AP Physics C exams. Sometimes the problem I tried to do out of the back of the chapter or on a worksheet I found was coming out wrong or I didn't have the answer to check it. Whatever it was I found that there were a few people I could ask for help. Most I knew personally through NCNAAPT but some I had met through my AP summer training or interactions online. I tried to spread out my questions, rotating through my "will help me" rolodex so that I did not take advantage of those willing to help me. I tried to figure it out by myself and not have to ask unless I was really stuck. My friends seemed to know this and did everything they could to help me when I asked.

Get trained:
I am a firm believer in proper science teaching professional development. Not all PD is good, don't get me wrong, but there are some consistently helpful training opportunities I always enjoy. For new teachers PTSOS and the Exploratorium's New teacher Institute of course. The national AAPT Summer and Winter meetings and your local AAPT meetings are full of the best-of-the-best resources shared among physics teachers. I find that the down-time in between workshops with other teachers can spark the best conversations and lead to lots of good shared ideas.

If the new-to-you course is an College Board Advanced Placement one you can also take a sanctioned AP training. They can be pricey but are often offered throughout the year. I had a hard time finding summer training for AP Physics C last year and had to travel to Texas to attend one. While it was helpful, I did not feel that one was enough to be comfortable teaching the course. I asked my district to send me to another one this summer and I'm crossing my fingers that there is more to learn.

Practice Practice Practice:
I found that, much like my students, I benefited from lots of practice. While I wouldn't do every problem in my textbook, I would probably work through twice as many as my students. I tried to do every conceptual question and did the ones that another AP Physics teacher using my book assigned. I figured that this more experienced teacher had probably already weeded out the problems that were too hard or awkward and these problems would be good for my students. Sometimes these still tripped me up and I decided early on that if I couldn't do the problem, I would not assign it to my students. By doing more problems I was able to see patterns in how the questions were asked or what they were asking for as well as improve my own problem solving technique. This also meant when it came to assessments I had more problems that I could solve then I had given to students to use.

One particularly helpful resource was an online workbook of released AP multiple choice and free response problems arranged by subject. This meant that I could look through the simple harmonic motion section and see all the problems ever asked on the AP exam about SHM. I could pick and choose the problems I wanted, combined with the textbook's test bank, to make my own tests. Sometimes working through all these extra problems seemed time consuming, especially if I wasn't going to assign them all, but overall it really helped my understanding.

Get organized:
This is easier for some than others, and I am not saying that everyone has to be a super clean desk all the time, but, if you are collecting new resources for a new class that doesn't do you any good if you can't find the cool thing your saved when the time comes. The easiest method is to create a folder for each unit and throw it all in there. At the start of the year I made a folder for each section of the AP Physics C objectives so that when I found a few resource I could sort it appropriately. This meant that prior to the start of the unit I would have maybe half a dozen to a dozen files before I really started to build the unit. As the unit progressed I would sort what I was using from the extra resources I wanted to keep from the assessments I would give. Since I tended to save everything I could get my hands on I would end up with a lot of files. For example, I started my magnetic field and forces unit with 5 digital files and two weeks later, before I've even written their test, I have 150.

Take care of you:
At the risk of sounding like a spa commercial, you need to take time out for yourself. Even though I was part time, developing new curriculum this year became my life. It was not unusual for me to work 12 hours a day, as in actual sitting down work, not just being awake for that long. I neglected my hobbies, cleaning, my health, because the work "had to get done." It will be the most work you've done outside of your first year to develop a new curriculum. Apologize to your family up front. However, do not lose yourself to it. Prior to this year I was trying to work on life-work balance and I failed miserably this year. I wish I had taken more breaks, spent more time with my kids, etc. but I didn't know how to get all my work done and do everything else. It got better as I developed this process and that's why I'm sharing. Hopefully having a game plan will help you develop your new-to-you course without drowning in your work. A burnt out teacher is not a helpful teacher.

To summarize:
1. Start with what you are given.
2. Try textbook resources.
3. Find reliable resources
4. Ask for help
5. Get trained
6. Practice Practice Practice
7. Get organized
8. Take care of you.

That's it, just 8 easy steps! (Totally sarcastic by the way)

It will be tough but by trying to focus on what I knew worked for me, I've almost gotten through it. As I can almost see the bright light on the other side believe me when I say you will too. Good luck!

Saturday, April 14, 2018

Resources ... In Color!

You have to have lived many summers to remember when "In Color" was appended to television show titles to distinguish them from humdrum black and white programs. Leslie Neilson spoofed the practice, along with everything relating to 1960s police dramas his Police Squad!.

I added color to my curriculum a few years ago. It began with writing a lab around PhET's "Color Vision" simulation coupled with pocket microscopes. The lab is called "Pixel Peeping" and it's a big eye-opener (!), especially when they look at the phosphors lighting up in yellow.

Next, I wrote an add-on activity called "Fun with Colors!" An interesting exploration of color mixing.

Then I saw this groovy video, and showed it in conjunction with the color activities. Biological pixels!

Science Friday: Where's the Octopus?


Then I saw this wee gem from Steve Mould, and thought to add it, too. How does your brain average red and blue when your green cone is silent?

The Royal Institution: Colour Mixing: The Mystery of Magenta


But I bristle at the notion of just showing a video or asking students to watch a video without having questions attached to ensure mental engagement. Otherwise, it's just watching TV. If it can't be done in class, it makes for great "YouTube homework."

So I put together some questions that could be answered while watching these brief clips.

Chromatophores and Trichromats

I had been using an iOS app to mix colors on my iPhone and iPad. But the app ecosystem is lively and active, so old apps die and new apps arise. An app developer named Insight currently offers an iOS app called Color Mixing. It has your standard color addition of primary colors (RGB) as well as color subtraction (CMY). It seems groovy, though I haven't tinkered with it much yet. I'm reluctant to develop an activity around such an app, since it may be gone tomorrow.

If you've got some groovy color stuff that works for you, post about it in the comments.

Sunday, April 08, 2018

Fluorescent Puffin Bills and Tetrachromacy

Serendipity. What a great thing among the scientifically curious.

Ornithologist Jamie Dunning’s serendipity compelled him to shine ultraviolet light on the already decorative bill of a puffin. And he saw something apparently not previously documented in the learned journals.

Birds, those opulent tetrachromats, are apparently up to their colorful shenanigans once again. We humans, humble trichromats that we are, just miss things sometimes. (It’s clearly not just the ability to fly that makes Naomi Hamilton Jealous of the Birds! But I digress.)

Read the story, behold the images, and mention it when you teach about colors and color mixing.

Puffin beaks are fluorescent and we had no idea.

Monday, April 02, 2018

Mechanical Universe High School Video Questions

Some of us are old enough to remember physics lectures. I may have even dabbled in that art during the first five years of my career. But its appeal faded as I placed increasing emphasis on more active learning techniques. The closest I get to lecture is guided discussion into a topic. 

We spend more time in laboratory, demonstration, and experimental activities these days.

But I do not banish all exposition as an enemy of learning. I outsource that task to the likes of Paul Hewitt (via Conceptual Physics Alive!) and The Mechanical Universe, especially the High School Adaptation

The High School Adaptation was originally released in oddly-grouped quads. For my purposes, I rearranged the episodes into sets that made more sense to me.

I couldn't show episodes of either series until I had question sets to accompany them. Active engagement in an otherwise passive activity, I suppose. The question sets I wrote for Conceptual Physics Alive! are distributed by Arbor Scientific. (You can get seven sets for free at the link.)

The sets of questions I developed to accompany The Mechanical Universe High School Adaptation episodes is now distributed at Teachers Pay Teachers: The Lessons of Phyz.

When I create a set of video questions for in-class viewing, I try to produce two different worksheets to diminish any wandering eyes tendencies of side-by-side table partners. I use a heavy font to increase legibility in low light since videos are often shown in diminished classroom illumination. The questions are to be answered while the video is playing.

The questions are also varied in type: fill in the blank, multiple choice, matching, and short answer. There are often illustrations involved in the questions. Importantly, these are low-level questions. They are not deep; they do not involve synthesis. They are not prompts for paragraph-length reflections. Their purpose is to keep students connected to the lesson in real time.

Too many video question sets I see strike me as impractical for real-time responses. They shoot for the upper reaches of the Bloom's Taxonomy mountain. I love high-level questions and use them as much as I can. But not during video play. Other question sets are wire-to-wire fill-in-the-blanks from the text of the narration. That's a bit extreme at the other end. I prefer to mix it up a bit while keeping it simple.

In any case, here are the sets of The Mechanical Universe High School Adaptation questions I've posted to TpT.

The Law of Falling Bodies · The Law of Inertia · Newton's Laws · Moving in Circles

Kepler's Laws · The Apple and the Moon · Navigating in Space · Curved Space and Black Holes

Conservation of Energy · Conservation of Momentum · Angular Momentum

Temperature and the Gas Laws · Harmonic Motion · Introduction to Waves

Electric Fields and Forces · Equipotentials and Fields · Potential and Capacitance · The Millikan Experiment

Simple DC Circuits · Magnetic Fields · Electromagnetic Induction · Alternating Current

Wave Nature of Light · Models of the Atom · Wave-Particle Duality

And now the bad news: If you don't already have the High School Adaptation edits of The Mechanical Universe, you can't really get them anymore. Intelecom had the distribution rights once upon a time, but it appears they have since dropped it from their offerings. If you're a card-carrying member of a library that subscribes to the Hoopla media service, you're in luck.

So much for my schemes of early retirement...




Monday, March 26, 2018

#GraphFail

You know it's a bad situation when the hashtag basically writes itself.

This first year of teaching AP Physics C: Mechanics and Electricity & Magnetism has had lots of lessons, one of which I was not expecting. I assumed (and you know the old saying about assuming anything) that students in AP Calculus or Multi-Variable Calculus could graph data. And I was wrong.

Well to clarify, they can graph but they often choose not to. Be it innate teenage laziness, prioritizing their overwhelming workload, or even just forgetfulness, my students don't spend the time on their lab graphs that I would expect. My expectations were laid out at the beginning of the year, as they were in regular Physics and I'm sure every science class they have ever taken. They are summarized below:

1. All plotted graphs (not sketches) should be at least a half a page in size and made on graph paper.
2. Axis and best fit lines should be made with a ruler.
3. Each axis should be labeled with the quantity and units. Each axis should have a uniform scale but it need not be the same from one axis to the other.
4. The graph should have a descriptive title (i.e. not "Graph #3").
5. If multiple data sets are plotted use different colors and/or different data point symbols. Include a legend.
6. Add a best fit line or curve to your data that gets as close as possible to all of your data points. Do not "connect the dots." If the best fit relationship is linear include a slope triangle to calculate the slope of the line.

I don't feel that any of these requirements are too extreme, strict or beyond what they are being taught in math class. Yet as the year has progressed I have seen the graph quality decrease. The occasional student "forgets" to do it on graph paper; I may let it slide. Once in awhile someone makes the graph too small and I'll draw an unhappy face on it in red pen. The mistakes were becoming more common but due to drowning in curriculum development I kept ignoring the growing problem.

But then it became too big. Last week I collected student lab notebooks with two labs in it. One required several graph sketches (just a variable labeled axis and a general shape, no plotting) with two plotted graphs and the other only required two plotted graphs. Students had begged for additional time for lab notebooks and after agreeing I joked that I was expecting perfection.

I did not get it.

It started with one unbelievable graph. Bad enough that I snapped a picture and posted it on my Twitter feed. Then there was another. And another. I collected enough of the "worst" that I decided that I had to have a little "talk" with my classes about quality of work. I assembled them into a powerpoint and planned the reckoning.

The big day was today and I had it all set up to make the big points in an amusing way, but letting them know I was serious. I started each class with, "I graded your lab notebooks. We need to have a bit of a chat. What math level are you in again?"
Students warily reply "Calculus..." because they know they're getting set up.
"Oh that's right," I reply, "So you should be able to make a graph right?"
They nod.
"Well, I thought so too, but we need to talk about that."
In one class a student said, "Oh man, she made it into a powerpoint, that can't be good."
I assured students that these contributions were anonymous, and that if their graph was included I still care for them and I know that they can do well in Physics. They just had a big "oops" with this graph. 

We proceeded to flip through the examples, with a mixture of roaring laughter (to the point of tears for some) and absolute disbelief.
They had questions:
"Someone turned that in?"
"Is that a hole in that paper?"
"What is that line even supposed to be doing?"
"Were these all from that one assignment?"

One student at the end said, "Wow, and we had extra time so you wanted them to be perfect." Yeah kid, I was shocked too.

In the end it was a funny way of reminding them of my expectation, and now I have a collection of some of the worst graphs I've ever seen. Of course I would rather not have had the situation at all but at least we can all benefit. The collection is available as a pdf and individually below. Feel free to use in your classroom for the same purpose, hopefully they help you avoid your own #GraphFails.

Only one data point really? No ruler used for the axis, not made on graph paper, no slope triangle and the best fit line doesn't even go through the single data point!

One of my students said that this apparent best fit line (that completely missed every data point) might be a Z-axis. I don't know if that makes it better. And no, seeing the grid through the back side of a blank piece of graph paper doesn't count. 

Not on graph paper, not made using a ruler and made a thicker line (potentially to hide poor data). Actually I don't even know if these data points are even properly plotted. We decided this was more of an artistic representation of someone else's graph than a graph itself.

Students often ask to use Excel, and they can, as long as they can use it right. This is not right. I have no idea how that best fit line worked with that data. 

These are supposed to be sketches, not plots, with a variable on each axis. That pen tip is for scale. Yes they are that small.

If you're asked to make a slope triangle on your graph it will probably be linear. When in doubt, the student apparently thought drawing a slope triangle would help anyway. 

When I said a "uniform scale on each axis" I didn't think I need to be specific and say you need more than one number to establish a scale.

Of course having no scale is worse. 

The large data points on this were annoying but not terrible. It was the sneaky breaking of the graph that they tried to slip past me.

When your data doesn't seem to have a trend, I guess plugging it into a calculator is one way of finding a best fit line. 

Then again, even if the best fit line seems obvious maybe you should use your calculator to double check. 

Sigh.

Thursday, March 15, 2018

Why California's musical road sounds terrible

When Honda produced a musical road in Lancaster, California a few years ago, I linked to their commercial and developed a lesson that included it. A Blog of Phyz post was duly posted.

The off-key result (and a bit of auto-tuning) bothered me. And I certainly didn't keep that a secret. I assumed it was an implementation error of some sort, and tried to invoke the notion that, "It's not that the dog sings well, it's that the dog sings at all!"

Creative science YouTube content creator, Tom Scott, did the legwork, er, wheel work to get to the bottom of this grooviness gone awry. It boils down to "centers" vs. "gaps". Take a look.

If you spend time distinguishing between random and systematic error, you'll want to add this to your curriculum there.

Why California's Musical Road Sounds Terrible


Scott refers to his source: Caltech's David Simmons-Duffin. Here's the well-crafted and thorough article posted at DavidSD.org way back in 2008. It really is well done, and he calls out Honda for auto-tuning the last two notes of the road, as did I. Spend some time and enjoy this post:

Honda Needs a Tune Up

Wednesday, February 28, 2018

A place for everything

Physics teachers hope to inherit or acquire useful lab apparatus. When I arrived at Rio Americano in 1986, the physics program had suffered through a year of long-term subs and mis-assigned teachers. Prior to that, the physics teacher was someone who was handy with tools and a fan of PSSC. We didn't have much, and what we had was dedicated kits aligned to the PSSC lab manual, conceived and produced in the post-Sputnik, pre-Apollo era.

I have had the good fortune of securing funds for considerable capital outlays for quality physics demonstration and laboratory equipment over the years. Rio's School Improvement, Gifted And Talented Education, Parent Teacher Association, and Science Boosters programs have funded a variety of my requests. It's been a patient siege, but in due time, the classroom was well-stocked for my needs.

When I did my student teaching at Ann Arbor Huron High, there was a physics equipment storage room the size of a regular classroom with rows of shelves: it was essentially an apparatus library. When I was a student in a physics class at Grand Rapids Central High, there was a classroom and a lab room. At Rio I have my classroom and share a tiny storage room with a neighbor. So what I get has to fit in a small, fixed amount of space.

Here are a couple of storage solutions I've adopted and continue to appreciate. Now that I teach four different physics courses, I often need to haul out or store materials in the wee breaks between classes. Half-gallon milk cartons, small utility tubs, and removable drawer storage are leveraged throughout the classroom.

The analog current and voltmeters stack nicely into the tubs and the tubs fit nicely into the drawers.

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Brass masses and mass hangers store nicely into strategically cut milk carts, and the milk cartons fit into the tubs. As do sets of disparate clamps.

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Flip a couple of the milk cartons for convenient tub stacking. There is no tubthumping.

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When the classroom was "modernized" in 2000, two storage cabinets were added. And promptly filled.

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I'm an unapologetic fan of removable drawer storage racks of all sizes.

Here are photos of lab sets of correlated items:

Dynamics carts

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After students have used the materials and it's time for clean-up, it helps to have a photograph of how the drawer should look when restored to its low-entropy status. Lay it on top when storing the drawer. I printed this latest edition (with the new Smart Carts) on heavy card stock.

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Circuits (batteries, bulbs, wires, switches, power resistors, capacitors, magnetic battery connectors)

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Magnetism (bar magnets, compasses, wires, lead-free solder, ignitor battery, rod clamp, collar hooks, wood dowel, Ampere's Law apparatus, Genecon)

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Wave Optics (CD, whiteboard markers, binder clamps, diffraction gratings, laser tripod)

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Clickers (each group is assigned four: e.g., Group E: E1, E2, E3, E4)

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The plastic removable drawers are also nice for storing class sets of a particular item, like force sensors.

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On the off chance that I've left you with the sense that I'm a fastidious neat-nick, I assure you that the rest of my classroom (and much of my humble abode) are ongoing celebrations of disorder.

Saturday, February 10, 2018

Gaussian Surfaces for the win

I worked all last weekend learning how to integrate the Electric Field near an infinite line of charge, finite line of charge, charged ring and charged disc. It was brutal. The only thing worse was working my AP Physics C students through it. Students are "supposed" to learn it, it's right there in the College Board Objectives for the course:

4. Fields and potentials of other charge distributions
a) Students should be able to use the principle of superposition to calculate by integration:
1)      The electric field of a straight, uniformly charged wire.
2)      The electric field and potential on the axis of a thin ring of charge, or at the center of a circular arc of charge.
3)      The electric potential on the axis of a uniformly charged disk.

Yet the concept is infrequently seen on the AP exam so some teachers hope for the best and don't teach it. I decided I would do a one day lecture along the lines of "Just follow me through the math kids!" I figured it was the best of both worlds, they technically saw it and some might remember it and I wasn't wasting much time. They did dutifully follow the notes but based on the pained expression they didn't "get it." I didn't like that every video tutorial I found said "And now you just check your integral table ...." because my students wouldn't have one on their exam. I told students the emphasis was on the relationships, what did and did not affect the strength of the field. I told students not to memorize the equations. If the problem did appear on the exam it would probably be for a partial charged ring, also known as an arc, which was done slightly differently and seemed much easier. Combine the not fun math and my inexperience with it and I was not a happy teacher for a few days.

So what do unhappy teachers do? Go back to good teaching strategies. My kids (and I) were getting confused so I made a reference table with a (1) a description of the situation with variables, (2) a picture that matched and (3) the final equation they got from the integration. Its available here as a pdf.

When I passed out the chart I asked them, "And what are we not doing with these equations?" and students answered "Memorize them!" So they tucked them away and may never have looked at them again.

A few days later as I was reviewing Gaussian surfaces I watched Dan Fullerton's APlusPhysics video about them. He pointed out that using Gaussian surfaces around an infinite line of charge you derive the same equation as in my chart above. My mind was blown. [cue explosion noises] When I lead students through Gaussian surfaces we worked through the derivation for the Electric Field around an infinitely long charged rod using a Gaussian cylinder. I had them take out their charts and pointed out the equation was the same as what we had found a few days ago. Then I asked them to look at the disk of charge equation and asked what it would look like as it became an infinite plane as R goes to infinity. There were audible gasps. "Wait, this is so much easier than that integration." Physics works kids. Gaussian surfaces for the win.