Day 153: Circuit Whiteboards

After about a week of investigating circuits and the current model, we checked our understanding by presenting whiteboards of a series of problems. The discussion was okay and any mistakes were quickly identified. We do a lot of ranking problems followed by a discussion to justify the rankings. At this point, students only have the current model with which to apply, so several of these problems are more challenging than they would be if the voltage model was applied.


  ##whiteboarding ##circuits  

Day 152: A New Approach to Circuits

This year in Honors Physics (a.k.a. AP Physics 1), we are using a combination of the Physics by Inquiry materials and the Modeling Instruction CASTLE materials. Our current model is based on the Physics by Inquiry investigations and the electric pressure (voltage) model is based on the Modeling Instruction CASTLE materials. I’m thoroughly enjoying the investigations that we are doing. Groups are engaged in careful observation and the construction of long chains of reasoning. I have the opportunity each class period to visit every group and have an in-depth discussion with each about their observations and conclusions. I ask each small group the necessary questions to expose their inconsistencies in their analysis and refine the model that they are constructing. Today, most groups analyzed the “pizza problem:”

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In this exercise, students are asked to predict the brightness of bulb A and B when bulb C is removed. Unfortunately, most groups made predictions and then built the circuit to check their predictions. Their prediction for bulb A was correct, but most groups simply accepted that their prediction for bulb B was either right or wrong and didn’t carefully consider why. I had to ask several questions before these groups realized that they didn’t have a good explanation for why bulb B should be brighter or dimmer, and that was the point of the exercise – to expose the limitation of our current model. This is also why the circuit is called the pizza problem: “What is greater? Half of a large pizza or all of a small?”

Next year, I will explicitly instruct students not to build the circuit for this exercise, but instead throughly defend their prediction to each other and me. I think they will more easily recognize the limitation of the model when they can’t simply observe that bulb B is brighter in the actual circuit.

  ##circuits ##paradigmlab ##setbacks  

Day 151: Deriving the Algorithm for Fractal Trees

In AP Computer Science, we are finishing our last unit before the AP exam. The summative lab is the Fractal Tree Lab. This year, students are provided much less direction. However, today, I did offer to work through the derivation of the algorithm with those students, who after working on it for most of day, wanted some assistance. They really just needed some help enumerating the key parameters for the recursive method and the geometry necessary to derive them. Here’s what we came up with:


I think the key idea is that the angle of the previous branch relative to the coordinate system needs to be passed as a parameter. This facilitates the calculation for the endpoints of the new branch. I’m excited to see if this year’s class is as creative as last year’s given that they have to struggle much more to derive the basic recursive algorithm.


Day 150: LOL Diagrams for Particle Physics

I love how some of my students continue to apply energy LOL diagrams long after we have finished the “energy” unit. In AP Physic B, we are in the midsts of an abbreviated particle physics unit. This group drew the LOL diagram for the collision of two high-energy protons creating a pion. The units for energy have changed to MeV, but the diagrammatic representation has not.


  ##particlephysics ##whiteboarding  

Day 149: Mass of the Top Quark

In AP Physics B, we are in the middle of an abbreviated particle physics unit. Since we are so close to Fermilab, I feel compelled to introduce students to the history of particle physics and the organization of the Standard Model. Fermilab has a number of fantastic activities that are prelabs for the Particle Physics Masterclass. Today, we used data from the D-Zero detector to calculate the mass of the top quark. It is fantastic to use data from D-Zero and to walk through the identification and calculations involved in a collision event. It is also a great way to “trick” students into reviewing and practicing 2D conservation of momentum problems in preparation for the AP exam! The results were fantastic. The average of two classes of data was within 1 GeV of the mass of the top quark.


  ##practicumlab ##particlephysics  

Day 147: Batteries and Bulbs

Today, we started the circuits unit in Honors Physics. We always start with the batteries and bulbs activity from the Minds of our Own video. In this activity, students are given a battery, light bulb, a piece of wire and instructed to light the bulb. Many students struggle to do this. I give everyone enough time to figure it out and to draw a diagram of four ways to accomplish the task as well as diagrams that are ineffective. We then watch the video and I congratulate them on bettering the Harvard and MIT graduates.

I’m really looking forward to this new circuits unit. My colleague who designed the unit has done an excellent job combining elements of the McDermott’s Physics by Inquiry materials and the CASTLE curriculum.

In addition to the battery and bulb activity, students made detailed and thorough observations of an incandescent lightbulb to determine how it works and why it is constructed the way it is. In past years, I’ve broken the glass bulb to make it easier for students to see the inner elements. This year, my colleague purchased 150 W bulbs with extremely clear glass. Students can observe the inner workings with the glass intact which makes handling and storing the bulbs so much easier.


  ##circuits ##paradigmlab ##equipment