SOCS-I The extended cut

"How We Teach and How Students Learn" (McDermott)
After reading this article, I am resolved to improve my teaching practices.  I can think of times during the year where I have worked to move away from direct instruction, and I have spent a lot of time discussing the types of situations described in the article.  For instance, the discussion on the brightness of light bulbs resonated with me.  I spent some time, after working through Kirchhoff's Rules,Ohm's Law, and graphing the current as a function of the voltage across a resistor and across a light bulb, discussing specifically the brightness of a light bulb.  In particular, I think it is difficult to describe what it is that makes a light bulb bright.  Is it the current through the bulb, or the voltage across it?  It is pretty clear, based solely on practical experience, that a 100W bulb is brighter than a 40W bulb in the home, but how does that relate to a set up in our lab.  I think the brightness of a light bulb is a complicated topic- perhaps more complicated than this article claims it is.  There are so many assumptions made in the typical questions that aren't necessarily obvious or true.  For instance, it is always assumed that the power rating of each bulb is the same, and that the resistance of the bulbs will be unchanged as the bulbs are added, removed or their connections are changed.  So, we talk about these sorts of things in my class, but gaining a good conceptual understanding of the brightnesses of bulbs in circuits is actually VERY difficult, and I am sure I do not have a clear model.

Now, I can answer the questions as long as I am willing to go along with the aforementioned assumptions, but I feel empty here-like I was "taught to the test."  As my students and I walk through our conversation on this topic, I feel like I am teaching to some future test for them (not mine.)  But I do wonder why the teachers at large seem to be in agreement that determining the brightness of a light bulb is somehow simpler or at least more approachable than finding the power dissipated by a resistor.

Now to a light bulb question I can really get excited about, can anyone provide a reasonable and (here's the kicker) simple model to explain the brightness of a 40W bulb connected in series with a 100W bulb?  I think I can do it, but it is going to require me to pull out the big guns, and if my students and I got into that conversation, a good many of my students would be running for the door.  Determining the current in that circuit would be a nightmare.  I mean, what is the resistance of a 40W bulb... connected in series with a 100W bulb?  I dunno, the wattage, as stamped on the bulb describes the wattage when the bulb is connected to 120VAC.  That will not be the case when it is in series with a 40W bulb.  Anyway, I digress.

I look forward to developing methods in this workshop that will allow me to walk with my students through questions, explanations and model building such that they gain a stronger understanding of the concepts of physics.  I have spent a lot of time in recent years making sure my test and quiz questions are assessing the kind of thinking and learning I am interested in seeing in my students.  Now, I hope that this workshop will help me make sure that my students' experiences in my class will better develop the kind of thinking and understanding I am looking for on my assessments.  I made this a "Instructional" type SOCS because I feel like I need to work the way I approach topics, and the way I lead students toward the light without pointing it out to them.  The workshop has been modeling that wonderfully for me, and I am so excited to practice these methods more.

And seriously, if you have a model for my light bulb question, I would love to talk about it with you.