Day 117: Refraction, Lenses, Inverted Images

Today, we tied up a bunch of loose ends related to refraction, total internal reflection, and lenses. We discussed the lenses lab and groups readily made the connection between the properties of images formed by converging lenses and those formed by concave mirrors as well as those formed by diverging lenses and those formed by convex mirrors. In an attempt to make these properties more relatable, we focused on examples of lenses being used in these different configurations. One example was the LCD projector. When I pointed out that, unlike the lab, the image from the LCD projector was not inverted, several students quickly countered that the image on the LCD in the projector must start out inverted. That led to a discussion about how the image projected on the retina of your eye must be inverted and your brain adjusts for that. Less than a minute after I shared that glasses exist that will invert the world, students found these:

Screen Shot 2015-03-02 at 11.52.35 PM

From that article is a link to a pair for $25. I’m very tempted. Anyone try these?

  ##optics ##equipment  

Day 116: Lenses Lab

Today, AP Physics 2 students completed the lenses lab. I was at a 6-12 science curriculum meeting; so, I left them with the same equipment as they had for the mirror lab but substituted lenses for mirrors. I’ll find out on Monday if they found the similarities of the properties of the images formed by lenses and by mirrors.

My colleague and I spent a portion of the day sharing bits and pieces of Modeling Instruction with 6th and 8th grade teachers. We did an activity with the constant-velocity buggies and Video Physics on iPads to create graphs of position vs. time and velocity vs. time. We then connected the video annotated with the position of the buggy to that of a motion map. We also shared interaction diagrams, force diagrams, and LOL diagrams. Everything was really well received and there is interest in a longer workshop in the future. It would be fantastic if students were exposed to these representations in 6th, 8th, 9th, and 11th grades!

  ##optics ##representations ##workshop  

Day 115: Refraction Activities

Today, AP Physics 2 students explored various stations exhibiting refraction phenomena. I didn’t take any new photos, but I’ll share an older photo of one of the stations inspired by a winner of the AAPT Physics Photo Contest:


A group of students and I had a really good discussion about how the observed phenomenon can be a combination of refraction and a lens effect due to the curvature of the container. I need to purchase some rectangular prism containers in order to demonstrate refraction without lens effects. Specifically, the pencil in water and oil and companion station to the three glasses in front of the colored paper would benefit.


Day 114: Ray Diagrams for Spherical Mirrors

Today, we started by comparing observations from the mirror lab and looking for patterns. After summarizing the properties of images formed by spherical mirrors, we worked on constructing ray diagrams for concave and convex mirrors. We drew three different cases step-by-step together as a class.

02 geometric optics.001

After drawing ray diagrams, I presented the mirror equation. Students now have three experiences with geometric optics – the lab, ray diagrams, and the mirror equation.


Day 113: Mirrors Investigation

Today, AP Physics 2 students determined the properties of images formed by spherical mirrors. I used the same simple equipment as I used to use in my Honors Physics course (meter stick, meter stick holders, mirror holder, lightbulb, small whiteboard) and terminology (for images: location, orientation, type, and size) but eliminated the cookbook lab procedure. The students worked through the lab determining the properties of images faster than with the cookbook lab and with greater understanding.


  ##optics ##paradigmlab  

Day 111: Physical Optics Exam

This optics unit is large enough, that I decided to have two exams – one on physical optics and one on geometric optics. Today, was the physical optics exam. Historically, I’ve presented geometric optics before physical optics. This year, to align with the Knight text, I presented physical optics first. Unfortunately, the version of the exam that I copied had a handful of refraction questions! As a result, students ended up with a shorter exam than intended once I told them which problems to skip….

  ##optics ##setbacks  

Day 110: Diffraction and Interference Lab Practicum

Today, students had two tasks:

  1. determine the wavelength of the laser
  2. determine the width of a human hair

The results were excellent. One group calculated a wavelength of 900 nm, but realized that wasn’t a reasonable value of the Helium-Neon red laser. Last year, I had students just measure the wavelength of the laser. This year, I added measuring the width of a human hair which emphasized what a precision instrument light can be.


  ##optics ##practicumlab