Thursday, June 4, 2015

Physics for Kids: Light

 I think we've settled into a pattern with the physics: the kids watch the Bill Nye episode related to the topic while I set up the experiments.

As soon as they finish, they are primed to  explore!

Light experiments are hard to photograph, but I got these LED finger lights a while back, partly to do light mixing experiments (they also make for great light up Easter egg hunts).

Kids are always told that yellow and blue make green (that's what the pipette and 96 well plate at the bottom are for: color mixing with liquid dyes).  This is true enough for pigment, but not for light.

If you mix all your paints together you get a muddy brown/black color.  If you mix all your light together, you get white.  I've done this before by taping colored lenses over flashlights, but the colored LEDs were easier, and there were enough for all the kids to experiment at once.

I also got to use my fancy set of lenses and prisms which I had picked up from a science supply store.  What worked best for us was to place, say, the convex lens against the wall and shine an LED through it, parallel to the wall.  You could see the patterns of refraction perfectly!

We also used my good spectrometer and a diffraction grating to look at the different wavelengths of light emitted by different sources.  We could also have used the home made variety, but my "good" spectrometer had calibrations so you can actually measure the wavelengths. I say "good" because it's less than $5 (actual laboratory spectrometers cost thousands).

We also looked at distortions caused by water.  The immutable "speed of light" is it's speed in a vacuum, light slows down as it passes through different densities.  Light moves more slowly through water than air, so if you put a pencil in a jar of water, it appears bent.

Interestingly, the kids were most fascinated by iridescence- the rainbow sheen of an oil slick.  In our case, we made it by dropping one drop of nail polish on to water (use a paper cup).  They were fascinated by the iridescence, by the rapid dispersion across the surface (changes in surface tension caused by the acetone base, I presume), and by the thin skin which hardened on the water surface.


In other Physics news, I also did a lesson on simple machines.  The possibilities for experiments here are endless, but I decided to try a different tack.  After they watched the episode, I asked them to show me an example of each simple machine using their Bionicles.

They did an amazing job!  I forgot to take pictures.  A video of their explanations would have been priceless!  But they were great! :)

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