As laser pointers became available to physics teachers, we took to puffing clouds of chalk dust, fog-in-a-can, or other particulate scattering agents into our classrooms to demonstrate the the magic of light amplification by the stimulated emission of radiation.
One year, I initiated a school-wide fire alarm during such a demonstration. The previous summer, the custodians had been tasked with cranking up smoke detector sensitivity to 11, unbeknownst to me.
Another thing we began doing was to shine our laser beams into water-filled fish tanks. The beams were again more visible when a scattering agent was deployed. Some used milk, some likes Pine-Sol. I used contact lens cleaning solution before settling on Mop-N-Glo.
But fish tanks were heavy, and the gallons and gallons of water made them downright unwieldy. It was a teacher-only demonstration activity.
As nice as it is for students to remember Physics as the class where the teacher did cool things, I wanted them to remember it was the class where they did cool things.
So I had my local plastic fabrication shop build "skinny fish tanks" (18" x 6" x 1", with a 4" foot). Less than 10 pounds filled with water. With these, each lab group got their own tank and laser: they got to run their own observations. Students loved that!
Here's a slideshow of some of the things we do with the skinny fish tanks.
Activities:
· transparency and the effect of a scattering agent (a little goes a long way)
· refraction (air into water and water into air)
· total internal reflection (students love this)
· gradual refraction (looming/mirages) (I like corn syrup better than sugar cubes for this now)
· diffraction (different gratings and different laser colors are useful here)
· scattering (I like Mini-Maglites and a generous dose of Mop-N-Glo for best effect) This one gets the most "wows" in a room of physics teachers.
It was such a hit (and so simple), I pitched it to Arbor Scientific's Peter Rea. So now they're available from Arbor.
They made a delightful video demonstrating some of the tank's capabilities.
When I show it to colleagues at conferences, my pitch is "I wouldn't say it's the iPhone of optics demonstrations, but other people might." Speaking of which...
One More Thing
I also put the tank on a low-friction spinner to demonstrate centripetal acceleration. And I stumbled upon this curiosity a few years ago, when I decided to spin the tank before stirring the food coloring. I have yet to find an explanation, but decided it's the mechanism behind geomagnetism. [For this demo, I used my 36" prototype, but the effect can be seen in the 18" models, too.]
I was just trying to demonstrate the parabola!
No comments:
Post a Comment