## Day 121: Geometric Optics Exam

Today, AP Physics 2 students completed the optics unit with the geometric optics exam. Based on first impressions, we should have practice ray diagrams more than we did. It’s hard to know with the new course how much to emphasize different areas. We didn’t solve any dual-lens problems at all. Based on my interpretation of the Essential Knowledge and Learning Objective statements, I think this is a reasonable decision.

##optics

## Day 120: Determining the Thickness & Refractive Index of a Mirror Practicum

Today, I tried a new lab practicum based on The Physics Teacher article, “Determining the Thickness and Refractive Index of a Mirror.” Through careful measurements of the reflected and refracted beams and graphical analysis, students determine both the thickness of the mirror and the index of refraction. The most challenging part of the lab was keeping everything aligned and accurately measuring the angle. The use of the level app on a smartphone made measuring the angle much easier. My first class struggled to make accurate measurements as we were trying to keep the laser level and angle the mirror and screen. After watching one group during first hour try various techniques, I encouraged second hour to take a different approach. They changed the angle of the laser and left the mirror flat on the table. This approached resulted in more accurate measurements.

##labpracticum ##optics

## 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:

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

##optics ##equipment