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30 November 2012

Article link: Keith Williams on the use -- and abuse -- of technology for technology's sake

Keith Williams is an engineering professor at the University of Virginia.  He visited me this week to see our new science building, talk physics and physics teaching, and to see what we do in our research physics course.  I was surprised and amused that, despite the fact that he grew up in and around Botswana, he ended up attending a Kentucky public high school, just like I did.

As we toured the new Manning Family Science Building he noted the enormous, beautiful lounge designed to facilitate collaboration.  Conversation turned to how I had told the architect in no uncertain terms that I didn't WANT network jacks, outlets, and cord guides on the tables to make it easy to plug in laptops.  Not only do I think such built-in technology will be outdated well within the building's lifetime, I object to the mere principal of making laptop use easy in this collaborative space.

Keith won the hearts and minds of the Woodberry science department when he complained about how every time he sees his students studying, they have their heads buried in a computer.  "They don't know how to talk to one another, to explain physics," he said.  

Keith was impressed that we had this section of the building devoted to human contact in the context of physics.  He liked even more our nearby open lounge with two large screens that can instantly connect to any laptop or tablet: this lounge says "Okay, if you're going to use a laptop to do physics, put the screen up where everyone can see it and talk about the physics."  We've found this arrangement to be wonderfully effective as our research team prepares their presentations.  

I'd encourage you to read his article in the Chronicle of Higher Education entitled "A Technological Cloud Hangs Over Higher Education."  He makes points about education technology much more eloquently than I could.  

29 November 2012

I'd do *anything* for a C... except put forth effort on homework, apparently.

Mr. Jacobs, I got a high D on the exam.  I know it's the next trimester, but I'm wondering, can I do anything to make the exam a C?  Can I do corrections, or extra credit?  I was really close to a C.

I actually got an email similar to this after our first trimester exam.  The student in question had done half-arsed homework since the start of school, and thus hadn't gotten the problem solving practice he needed in order to perform well on the exam.  I was rather surprised.  My juniors and seniors don't make such requests.  They know the score: be ready to perform on the exam, 'cause that's what goes on the report card.  I assumed that freshmen would understand that principle as well; my first reaction was to wonder to myself what kind of fluffy middle- and elementary- school teacher had given this student the thought that begging for a grade might even possibly be successful.  

But how to respond?  I'd like to reply simply "NO."  But the last thing I need is for him to complain to his mom, "I asked Mr. Jacobs what I should do about my exam, and he was mean to me!  He doesn't like me because I did badly."

So I put the response in terms of athletics, something like 

"Nope.  Did Episcopal High School ask the referee if there was anything they could do to change the score of the football game they lost to us?  I mean, maybe they could have another chance to catch that touchdown pass they dropped, or maybe they could get a second opportunity to tackle our running back.  Right?*

Learn from the experience.  Prepare better not just right before the next exam, but all trimester.  See if you can improve next time."

* If the student were, say, a Patriots fan, you could say something like "Can the Patriots ask the commissioner if they can do anything to let Wes Welker catch the wide open pass that would have won the Super Bowl?  I mean, they were so close..."  Yes, twist the knife with a very personal sports reference if you can.

25 November 2012

Review packet for conceptual physics trimester exam

My review assignment for the 9th grade first
trimester exam is available here.
It's a fool's errand to expect high school students of any age to simply "study" for an exam without giving them some sort of clear guidance.  And just saying "go over your old tests and problem sets" doesn't cut it.

I've always been in favor of creating assignments -- whether as part of the course right before the exam, or as an extra credit opportunity outside of class -- that themselves serve as effective exam preparation.  Perhaps the most diligent students will do more than just exam review assignments, but you can ensure that everyone has at least done a measure of preparation.

My 9th grade cumulative trimester exam included "justify your answer" questions to the tune of 60% of the exam.  We've certainly practiced justifying answers all year on homework, but since these questions take time to answer, I've only been able to ask a few of these on each test.  I needed to prepare the students for increased scrutiny of their justifications on this exam.  

Yet, I didn't want to make a review sheet entirely of "justify your answer" questions.  A review sheet doesn't help unless it's taken seriously, and done RIGHT.  Without me standing there grading their responses, the students wouldn't have gotten appropriate feedback on a full set of "justify your answer" items.

So instead I mixed in some multiple choice with some more complex items.  Many of the review sheet questions were "multiple correct," in which multiple choices were listed but any number of them could have been a correct answer.  Some review questions were ranking tasks.  Others required a numerical answer, with units.  Here's a copy of the sheet.

Point is, each question came with a huge box for the answer.  At our nacho party before the exam a teacher could quickly mark each response right or wrong; sure, it's not a scantron, but grading this was simple because we could just look at what was written in the big box.

THEN, the students had a few days before the exam to correct their wrong answers with a clear justification.  No credit was awarded unless all the corrections were done; credit was awarded based on how many of these corrections were actually, well, correct.

Interestingly, I discovered that my freshmen were just as diligent (or sometimes not-diligent) as my seniors at doing the assignment and the corrections -- about 90% of the 9th grade class turned in the corrections on time and with appropriately attempted responses, in line with what I used to get from seniors.  But, my freshmen were way LESS diligent about getting the correction right.  A whole bunch of them wrote utter BS as a justification; they failed to collaborate with their classmates or with me.  And, most of these students made mistakes on the exam similar to their mistakes on the review packet.  The moral here:  practice doesn't make perfect, perfect practice makes perfect.  Thank you, Bosco Brown of my old marching band, for etching that saying into my brain's permanent storage.  

So for NEXT trimester's exam, I'm going to have to think of a way to make the students get the corrections right.  I'll let you know what I come up with; the suggestion box is in the comment section.

21 November 2012

First months of 9th grade conceptual physics: non-cumulative material

The diagram to the right shows a mirror.  On the diagram, draw a dotted line representing the normal to the mirror's surface.  Justify your answer.

Conceptual physics covered ray optics as the first topic of the year, back in September.  We then moved on to waves, and to circuits.  Part of the reason for this sequence was because these are easier topics than the typical kinematics and forces opening gambits.  I want freshmen to adjust to boarding school life a good bit before I hit them with the hard stuff.  But the more important reason for this sequence is that it's not sequential at all.

Kinematics and forces are self-referential.  It's important to internalize a definition of acceleration, which is used in every context imaginable.  Many force problems require kinematics to solve fully, and vice versa.  Then in whatever topic is next -- usually either energy or momentum -- it's assumed that students are comfortable with forces and motion.

This approach works fine with my seniors, because they usually are in fact reasonably comfortable with forces and motion by the time I move on; and because even the slower students have enough background that they can become comfortable.  Seeing forces and motion in new contexts provides extra practice and encouragement to review previously-discussed physics.

Freshmen, though, can be absent mentally for much of our first trimester.  It's not that they don't want to do well -- just the sheer overwhelming nature of life without mom and suddenly with 400 siblings, coupled with the rate at which they're growing physically and mentally, can mean they don't remember information day to day, or even minute to minute.  At the senior level, I'm assuming a level of personal organization, daily focus, and self-driven practice that freshmen can simply not fathom.  

We just gave our first cumulative trimester exam.  Some did great; some did terrible.  My point here is, how they did this trimester doesn't matter that much to the students' overall success in the course.  When we move on to kinematics after Thanksgiving, it won't make any difference at all whether they remember whether light bends toward or away from normal.  I don't HAVE to go over the exam, I don't have to review anything; we can move on to new and different stuff, knowing that everyone can understand it in isolation from the first trimester.  Then I can sprinkle some review in over the course of the next six months in preparation for the final exam in June.

The question at the top of today's post shows one of the "justify your answer" questions on the trimester exam.  We've learned that the "normal" is "an imaginary line perpendicular to a mirror's surface," and we've extended that definition in the context of refraction across a boundary between materials.  This question requires the student to recognize that the normal is not perpendicular to the bottom of the page, but rather to the optical instrument in question; the justification just requires some statement of the definition of normal.   

So why do I ask this question on the exam?  Because it is the ONLY question I can think of that is truly cumulative with other topics we will be teaching this year... when we get to "normal forces," we'll have seen the word before; and we'll even have seen an explicit situation when the normal is at an angle to the vertical.  

16 November 2012

Ray diagram practice sheet

Our conceptual classes need to be able to handle ray diagrams for converging and diverging mirrors and lenses.  That's really only six different diagrams:

  • Converging lens with an object inside the focal point
  • Converging lens with an object outside the focal point

  • Diverging lens*

  • Converging mirror with an object inside the focal point
  • Converging mirror with an object outside the focal point

  • Diverging mirror*
*The ray diagrams for diverging instruments are essentially the same no matter where the object is located.

Since this is conceptual physics, I don't ask them ever to use the thin lens or magnification equation to predict the location and size of an image.  We use ray diagrams, and then estimate distances based on the scale of the diagram.

In preparation for our exam, I handed out this practice sheet.  It presents the six different situations above, with an appropriately-sized mirror or lens, with focal and center points already labeled, and an object already drawn.  If a student can fill out this sheet correctly, he's ready for any question I can throw at him on the exam.

You can use these diagrams as a basis for your own questions or your own review sheet:  one idea is to change the focal length in the text of each problem, so that each student has a different focal length.  They will see, then, if they check their answers with each other, how the diagram can look the same but the different scale leads to different values for image and object distance.  

You can also copy the diagrams into "paint" or some graphic design and manipulation program.  That will allow you to change the diagram itself, perhaps by moving the object closer or farther from the lens, or changing the focal lengths.  Every time I need to construct a question about lenses or mirrors, I use these diagrams as a template to adjust whatever parameters I need to adjust.


07 November 2012

Circuit building challenge -- a last-minute class idea that worked

On Sunday night when I went to bed, I had no clue what to do on Monday in conceptual physics.

The problems were, about a quarter of my students were going to be on a field trip; and everyone has half-expected the headmaster to declare a free day each day since a week ago Wednesday.  I know enough to plan for the spontaneous one-day vacation by padding my lesson plans.  This year, though, the free day never came.  So I was out of material, and I couldn't just push on to a new topic with so many folks gone.

A day like this calls out for "enrichment."  Show a Julius Sumner Miller video.  Read a chapter of Surely You're Joking, Mr. Feynman.  Play "Crayon Physics Deluxe."  In the shower Monday morning, though, I had an even better brainstorm for freshmen in a circuits unit.

We have taught the freshmen how to deal with resistors in series and in parallel.  However, rather than make explicit calculations, we have taught the art of ESTIMATING the voltage across each series resistor, and the equivalent resistance of parallel resistors.  Why not, I thought, use my extra day of class to refine my students' estimation instincts?

On the board, I listed each of the resistor values I have available in my lab, including 130 ohms, 68 ohms, 57 ohms, 47 ohms, 41 ohms, 20 ohms, and 15 ohms.*

*Okay, really these are all KILOohm values.  I can't use 41 ohms with a 14 V battery, because that would dissipate 4 watts with quarter-watt resistors, and then Bob help us all.  But the 9th graders don't have to know that, since we're not measuring current!  I called a 41 kiloohm resistor a "41 ohm" resistor; all is peaceful, and all measurements are correct.

I handed each group of two a sheet that said:

You have a 13.8 V battery.  Build a circuit in which one resistor takes _____ V (+/- 0.3 V) across it.  When you have it correct, draw a diagram of the circuit in the space below.

In the blank I wrote a random number between 1.0 and 12.0.  They were allowed to use any combination of resistors.  At first they tried to make calculational guesses; finally they figured out that the best strategy was to just choose some resistors, try it, and then choose some new resistors.

What a wonderful exercise!  It was modeling at its purest... eventually each group got the intuitive idea of a proportional distribution of voltage across series resistors.

Next, they got a different sheet:

Build a circuit which has an equivalent resistance of _____ ohms (+/- 1 ohm).  When you have it correct, draw a diagram of the circuit in the space below.

This time, the number was between 3 and 100.  I made sure that the answers were never truly trivial, i.e. equal to one of the resistors in the box.  Some groups even figured out -- with minimal if any prompting! -- that they could get a 10 ohm resistor in series with a 20 ohm resistor by using two 20-ohmers together in parallel to get the 10 ohms.  This even though we never once discussed combinations of resistors in both series and parallel.  

This day turned out even nicer when I found out that too many students hadn't completed their quiz corrections from last week.  The ones who were done with corrections got to play with circuits, earning candy and extra credit for each successfully built circuit; the others got to sit in the meeting room finishing corrections before attacking the circuits.