Gas station without pumps

2012 April 5

Physics lab for chapter 8 but not 9?

Filed under: home school — gasstationwithoutpumps @ 21:22
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Chapter 9 of Matter and Interactions is a return to mechanical energy after Chapter 8’s detour into quantized energy. I wanted for us to come up with a lab experiment for this chapter—perhaps something with moments of inertia (based on 9.P.36 or 9.P.39, perhaps), but I haven’t yet come up with anything that seems both fun and worthwhile.

Handheld diffraction spectroscope, image from

I think that on Apr 6 we’ll mainly go over the Chapter 9 homework and do a little detour for a Chapter 8 lab:   I bought a cheap diffraction grating spectroscope, and we can look at spectral lines of various light sources.  The obvious ones are fluorescent light bulbs, LEDs, neon bulb, Xenon strobe bulb, sodium salt in a gas flame, and perhaps monochromatic light from laser pointers (reflected off a white background—not directly into the spectroscope!).  Perhaps we could even look at the red, green, and blue filtering of the backlight of a computer monitor.

Although the spectral lines we can observe don’t correspond to the ones discussed in the book—I can’t make mono-atomic hydrogen at home, nor do I want clouds of hydrochloric acid gas.  I suppose we could heat iron to red heat with a torch, but I’m not sure that there is much point to that—we’re going to have a hard enough time seeing bright light emitters, given that the class happens in the early afternoon and we have a lot of windows and skylights, with no way to darken the room.  The closets in the house are all too full of “stuff” to be useable as darkened rooms (even if there weren’t cat dander allergy problems).

One problem that the spectroscope had was that the entrance slit was rather wide and had a rough edge.  This made the lines of the spectrum rather broader and blurrier than they needed to be.  I fixed this with a little electrical tape, using the edges of the tape to create a narrower, cleaner-edged slit.

Electrical tape was used to narrow the slit on the spectroscope and give it cleaner edges.

I tried taking a photo of the spectrum of a compact fluorescent light bulb. Several of the fainter lines did not come out well in the photo, but the main lines are pretty clear.

Spectrum of a compact fluorescent lightbulb as seen with the handheld spectroscope.

1 Comment »

  1. […] for the green laser (520 nm) and a diffraction grating with 1000nm ruling. I also passed around a $7 spectroscope that I had bought for homeschool physics and had students look at the fluorescent lights with […]

    Pingback by Fourth day of freshman design seminar | Gas station without pumps — 2014 January 16 @ 00:26 | Reply

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