Two wrongs certainly don't make a right...

Today in my astrobiology class, I was talking about Saturn's rings and ringlets and I showed this photo:

This is an image of Saturn's F ring as imaged by the Voyager 1 space probe in 1980. We were discussing the ring structure and I was showing that some parts of the rings were not perfectly circular. This is due to the gravitational effects of the small moons near the rings on the ring particles.

But in talking about the ringlet in this photo, I was also telling the class about the camera technology on the early space probes.  I said that the Voyager camera was actually a film camera. Space probes with film cameras have the capability to process the film on board and then used a scanner to digitize the image for transmission to Earth.  It's a great strategy that was used before digital cameras were regularly put on space probes.

Except, the Voyager missions didn't use film cameras.  Oops.  Guess I'll issue a retraction next class.

But on my train ride home I was reading my current book: That's the Way the Cookie Crumbles: 62 All-New Commentaries on the Fascinating Chemistry of Everyday Life by Joe Schwarcz when I realized I had made a mistake in my OTHER class that I'm teaching.

Yesterday in "Light and Atoms" we were talking about what holds water inside a capped bottle having a hole on the side of it. (Answer: the air pressure of the room holds it in until the cap is loosened.) But the topic of surface tension was raised by one student.  So I turned on the water faucet and splashed the water around in the sink with my hand.  I asked if the water molecules were being held together by chemical bonds and if so, was I producing a chemical reaction to break the bonds as I splashed the water around.  (My answer was no, which it still is, but it was still part of the mistake.)  I then went on to explain what surface tension means and how you can lower it with a tiny bit of soap.

Except that surface tension depends on the weak hydrogen bond between water molecules.  I didn't talk about that.  So, I may have left the class thinking that there is no chemical bonding between water molecules.  Clearly that's not true.  The mistake I made was mixing analogies.

I'm quickly trying to learn more about hydrogen bonding so I can figure out how to correct any confusions I may have introduced.

Reflections on reflection.

Today in "Light and Atoms" we looked at the ray model of light. The goal was to be able to understand how the rays from a light source (or object) behave in order to use ray diagrams for curved mirrors and eventually lenses.  We spent quite a bit of time on our discussion and had to rush through the activity at the end.

I handed out plane mirrors, corkboard and pushpins for a law of reflection activity.  Many of the students had to leave before they completely finished the activity, but those who stayed really liked it. That's definitely a keeper activity.

The lab we did today was a lab exploring the formation of images by converging mirrors. I had the students use the lab writeup in their textbook.  I got the sense that while the class completed the lab all right, I would be surprised if most of the students actually understand the reflection off concave mirrors at the level the lab was written at.  One of the TAs even commented that there are some labs which do not work well to facilitate learning and that this was one of them.

I don't have any answers as to how to better teach reflection off of curved mirrors.  I need to refer to some of my favorite sources for inspiration.