On Friday I was back at Primaria, building on
what we learned last time about colors of light. I handed out diffraction
gratings again, so they could again see how white light is composed of colors.
(I have my doubts that they really get the message that white light is
composed of colors; what they take away seems to be that the device
makes rainbows appear, which is not at all the same thing. Maybe a
dark room with a single source of light would help.) I asked them to
list the colors in order of appearance, in English and Spanish. I was
surprised to see how much trouble they had listing them in order of
appearance on the diffraction grating; they were all over the map. One
idea for the future is to have them draw what they see. But I was
even more surprised when they burst out in song "Red, orange, yellow /
Green, blue purple" when they realized that I was essentially asking
for the colors of the rainbow. They had memorized this song which
perfectly described what they were unable to describe when asked about
their observations! There must be something I can learn from this,
but I'm not sure what.
I wrote the names of the colors in this order on the board, so that
"range of colors" had a more concrete meaning. Then I asked them if
there could be anything "before" red or "after" purple (aka violet).
One boy in one group actually guessed infrared, presumably because he
had overheard me use that word to a teacher. I briefly mentioned
ultraviolet to connect it with the need for sunscreen in summer, but
the main purpose was to show the infrared camera. Things at room
temperature shine in infrared light, and the warmer they are the more
they shine, so the infrared camera is really a very different way of
looking at the world. You can walk into a kitchen, as we did, and be
blinded by the water boiling on the stove. A hand holding an ice cube
looks like a bright silhouette with a black rectangle in front of it.
People glow...you can see the glow radiating out from the openings in
their clothing, and from under their hair. You can make your way in
the dark, because everything is glowing to some extent. You can find
people hiding in the dark.
One group insisted they could see in the dark with their own eyes, so
I took them into the only room in the school which has no window: the
adult bathroom. (Linus had previously voiced this "I can see in the
dark" meme with great confidence, so I was sure it was something that
kid in the school bragged about and needed to be refuted.) I was
pretty sure that when we got in there and shut the door, most kids
would be scared and admit that they couldn't see in the dark. That
happened to one child, but several others were perfectly content with
the light coming from the gap under the door and said, see, we can see
in the dark. Preconceptions are very difficult to uproot! I
discussed this with Linus later and we agreed that he could see when
it was kind of dark, but not when it was perfectly dark. So
terminology matters. Given a way to save face, I got him to agree
with my scientific conclusion; but I had to give him a way to save
face. In any case, the little bit we could see in the mostly-dark
bathroom was nothing compared to how well we could see with the
infrared camera!
I also showed how the IR camera could see through some things which
are opaque to visible light (eg, a black plastic garbage bag, and I
mentioned but did not demonstrate smoke), and others are opaque to IR
but transparent in visible light (eg, glass windows; when I pointed
the camera at the window we saw only my reflection on the camera
display). Outside, the sky is black even during the day because the
air is relatively cold.
If all this sounds interesting, I recommend you watch this video to
get an idea of what the world looks like in the infrared. Meanwhile,
I have to make some notes for future demos: (1) it was hard for
everyone even in a group of seven to see the display. I thought I had
solved this problem by bringing a laptop and not relying on just the
camera's small screen, but you cannot imagine how seven kids have
trouble seeing the same laptop screen at once. In addition, the latop
screen was small enough that it didn't really grab their
attention. Next time, I will either bring a large LCD display, or use
a projector. (2) This activity is not very hands-on. The kids had
trouble staying tuned in. It would be good if I had the camera on a
fixed tripod out of their reach, set up a giant display with the
projector, and just let them do things and bring things in front of
the camera.
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