# 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:”

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.