Today we started the Nuclear Physics unit in AP Physics B. While introducing the concept of binding energy, it struck me that an energy LOL diagram, where the mass of the atom before and after is treated as an energy storage mode, would clearly demonstrate the concept. I have never used LOL diagrams in the context of nuclear physics, but, for the first time, students this year are familiar with them. Here’s an example LOL diagram illustrating the energy required to remove a neutron from Carbon-13.
Later in the lesson, I sketched an LOL diagram to demonstrate the decay of Radium and that no energy is added to the system:
I think this will make nuclear physics more accessible, less mysterious, and reinforce the conservation of energy concept.
Yesterday, the BICEP2 collaboration announced their results which indicate detection of gravitational waves and direct evidence of cosmic inflation. While the plan for AP Physics B was to start the unit on nuclear physics today, we postponed that to talk about these results and the broader context needed to appreciate their significance. In AP Physics B, we do enjoy a cosmology unit after the AP exam, but I decided to introduce the ideas of Hubble expansion, cosmic microwave background radiation, the big bang and inflation today to provide context.
Students appeared to enjoy the change of pace and asked some really good questions. Some of which I was able to answer; some of which physicist are still trying to answer. I hope that every student left with an appreciation that physics is a dynamic field, there is a lot of questions left to answer, and we live in the golden age of cosmology.
Honors Physics continued investigating the charged particle model (CPM) with pith balls, vinyl, wool, acetate, and cotton. They are doing well creating the long chains of reasoning necessary to explain their observations. We’ll see how they do when introduced to the electroscope and charging by induction tomorrow.
Although it sounds strange, I encourage students to put themselves in the shoes of an electron and ask themselves, “What would I do?” This helps them focus on the movement of electrons (as opposed to positive charge carriers) and consider what is attracting them, repelling them, and what options they have for movement (based on insulating or conducting material or a path to ground).
The weather is cooperating. While I’m ready for Spring, I hope electrostatics continues to work this week!
There is a tradition during Spring Week that groups of seniors organize, prepare, and perform in Airband. I assume that Airband started as a lip-syncing competition but has grown into quite a sophisticated production. The groups competed Thursday night, but the top three also performed at the Spring Week assembly today. The top group was The Last Airbanders. Their performance was fantastic and very creative.
Today, in Honors Physics, we left behind mechanics (oscillating particle model) and made the huge shift to start the charged particle model (CPM). We started our exploration of electrostatics with the classic sticky tape lab. The students made careful observations and readily proposed a reasonable hypothesis for most of the observed behaviors. However, when I asked why the paper strip was attached to both the top and bottom tape, they were stumped. So, devising an explanation for that behavior became homework.
The following whiteboard is of Giancoli Physics 5e, Chapter 28, problem 42. One of the big ideas in the AP Physics B unit on atomic physics and quantum effects is that Heisenberg’s Uncertainty Principle describes a fundamental uncertainty in the universe regardless of the measurement uncertainty of the technology being used to perform the measurement.
The student completed this lab last Wednesday when I was gone. One student needed to make up the lab this afternoon; so, I took a picture of the apparatus. The AP Physics B class does the photoelectric effect lab in the unit on atomic physics and quantum effects. I have an old PASCO h/e apparatus which is probably irreplaceable. I have students complete a series of prefab questions where they use the wave model to determine how changes in intensity and frequency affects the stopping potential and then they use the particle model to determine the same. After conducting the lab, they state which model fits their observations. They also graph stopping potential versus frequency which allows them to determine the work function and Planck’s constant. Great modern physics lab.