Those of us teaching physics have made a lot of changes this year. One major change is a focus on depth of understanding and critical thinking, which results in fewer topics covered. While I have qualitative evidence through formative assessments that students this year have developed stronger critical thinking and long-chains-of-reasoning skills, I’ve been bothered that I don’t have a summative assessment to measure this. Ideally, I would like an Force Concept Inventory pre-test/post-test equivalent for critical thinking. I’ve bookmarked the College and Work Readiness Assessment (CWRA), but that isn’t an assessment that I can administer to my own class. If you know of another, please let me know!
Due to our crazy calendar and snow days, seniors graduated two weeks ago and I’ve had relatively few students in my regular physics classes since then. We’ve been investigating color, polarization, mirrors, and lenses. Since these students had already completed their final with the seniors, I decided to use the scheduled final exam time this week to try a critical thinking assessment. I wanted them to read a passage that describes a physics phenomenon with which they were unfamiliar, make several observations of a somewhat related physics phenomenon that they had never seen, and propose and defend an explanation for this observed phenomenon based on the prior knowledge. They read about diffraction, observed various wavelengths of light passing through various double slits, and tried to formulate an explanation. We had previously learned about interference of waves (slinkies and beats), but not in the context of light. This is quite a series of inferences and connections for students to make during a final exam; so, I prepared a series of guiding questions to help them make the connections. When a student said they were stuck or were off-track, I gave them one of the five guiding questions. Some students needed all five; one, amazingly, didn’t need any.
Here is my reading passage, observation procedure, and guiding questions:
Download (PDF, 231KB)
The students did quite well connecting what they read about diffraction to what they observed to what they already knew about interference. Here are some of my favorite student comments.
The black parts are shadows, I think we see them because the light is being destructed?
In order to have constructive interference, one ray must travel one wavelength further than the first.
The blue filter causes the lines to be closer than that of the red filer because blue has a shorter wavelength and when it travels to the plate, it forms more concentric circles. Thus, there are more intersection of circles and more lines formed.
and my favorite (written without any guiding questions):
… It’s like light beats.
I also had some really creative explanations of the interference pattern. Students mentioned internal reflection in our eyes as well as lens effects due to the slits.
Students commented that this was unlike any final exam they had previously taken. In fact, several students in one class didn’t want to leave until they were satisfied they had a complete explanation. It certainly seemed more worthwhile than giving students a list of equations and a set of problems with numbers for them to plug in on their calculator. I think there is a kernel of a good idea here, but I need to develop it more. In my largest class, it was hard to manage since I had to interact with each student during the assessment, read their explanations, and give them the appropriate guiding questions. Sometimes this required me asking my own clarification questions and the ensuing discussion could be overheard by other students. If you have tried anything like this, please share your experience!