Day 14

Friday. So I am excited for WSST 2015 in Wisconsin Dells (March 5-7 I believe). From the WSST website:

Keynote Speaker: Prof. James Kakalios


James Kakalios is the Taylor Distinguished Professor in the School of Physics and Astronomy at the University of Minnesota, where he has taught since 1988. His scientific research in experimental condensed matter physics concerns the properties of complex and disordered systems. His class “Everything I Needed to Know About Physics I learned from Reading Comic Books” is a popular freshman seminar.

He has been the science consultant for films such as The Watchman and The Amazing Spider-man. James Kakalios has authored two books that explains science in a fun and entertaining way.

So yeah, me and that X-Men comic are stoked for the conference this year.

Physical Science: So we talked about the results of the measurement activity from yesterday. Basic outcomes amounted to:

– if people use different devices, use them differently, or use different sizes for a scale, we don’t get comparable data.

– We end up having to make an estimate in nearly all cases in order to get a measurement, as no every item out there I exactly a multiple of the size of the device we use.

This all leads to the discovery that we really need to use a Standard of Measurement: Everyone agrees as to the magnitude of a measurement, and how to use a device for measuring. We also talked about how when we take measurements in science we always end up making an estimate of some sort, as we report all known values the device tells us, plus one more that is estimated.

We plan on putting all this to the test this coming week.

Chemistry: We also dealt with measurements. As for reading scales and taking the proper measurements, students did well. We did run into some issues when it came to do calculations and tracking sig figs. For a first time effort though, I am pleased.

Physics of Light: We started out with a little activity that relate to the pinhole camera. one of the things we have been discussing is how that pinhole camera only works if there is sufficient light selection (only a small number of light rays/streams of particles from a given point on a source, can get through the pinhole). So I had kids take out a handout I gave them that had a small smiley face on it. to see what it looked like.

Images were also posted a couple days back.

Smiley viewed from about 2 cm away.

Smiley viewed from about 2 cm away.

From this close up, there are way to many light rays bouncing off of the paper and entering our eye. This is just like having  large pinhole, to much light and you get a blurred out reproduction.

Then we tried holding a playing card between us and the paper. One of those playing cards that has a hole punched out through the deck. Since the hole is bigger than than the smiley face, there was nothing different. Then they tried a note card with an actual pinhole in it.


And success!

Same setup, but now through a pinhole. :)

After this we talked some more about some of the observations we made, including when we put multiple pinholes into the camera. This resulted in multiple reproductions, and the diagrams make it clear why. Then a student asked about interpreting what they had seen the day of the activity.

“When we did ours, the reproductions overlapped, and some of the black “L” shape looked grey. Why was that?”

Students managed to bridge that observation to that if the penumbras we had observed during the Shadow Lab. Since a light part from one pinhole had overlapped with the black part of another, it looked grey. It was also noted that besides being grey, it was also a little blurrier.

We also looked at how really, multiple pinholes might be doing some selection of light, but really they let more in. We used the diagrams to show that when the pinholes get closer together, the light rays begin to overlap and if they are so close that there is no discernible barrier between them, then they are really no different then a large pinhole.

Finally we went back and talked about another observation that came up during white boarding: The light rays spread out further from each other on the screen when they have to travel further back to reach a screen. Some students thought that this resulted in more light rays being able to reach the screen, thus explaining why the reproduction seemed clearer.

I pointed out that there can’t be more light rays hitting the screen, as no more or less rays come through the opening. Another student pointed out the geometry of the situation.

“If the particles travel in straight lines, then they spread out more, which is why the reproduction gets bigger. But that also means that the light is more spread out and it should be darker. Shouldn’t it?”

Guess we’ll have to investigate that on Monday.


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