Posts Tagged With: science experiments

Simple Homemade Spectroscopy

I love chemistry. I get to play with fancy instruments, do some experimenting, and act all sciencey and stuff. Next week, for example, I get to play with a nice spectrometer and do some mathjitsu on spectral stuff. Anyway, I decided to see if I could build a simple spectrometer myself. Five minutes later I learned how to build a simple device out of cardboard, some tape, and a DVD. An hour later, and here’s my spectrometer:

Homemade Spectrometer

Homemade Spectrometer

This spectrometer was designed by PublicLab.org–a nonprofit community science organization. The kit for the spectrometer can be purchased on Amazon, but I built mine from schematics provided by PublicLab.org.

It’s really an amazing spectrometer for its simplicity. Light enters a tiny horizontal slit at the front of the box and passes through a diffraction grating made from a piece of a DVD. Essentially, the light coming through the narrow slit hits the DVD which splits the light into the wavelengths that compose it. What you see looking through the DVD lens is the line spectrum of the light source. A good explanation of the tech and the underlying science can be found here.

So let’s take a look at a few emission spectra (Note: Usually you see spectra oriented horizontally, but these are oriented vertically… same thing different perspective):

Spectrum of sunlight through clouds

Spectrum of sunlight through clouds

Spectrum of Fluorescent Lightbulb

Spectrum of fluorescent light bulb

Spectrum of Incandescent Lightbulb

Spectrum of Incandescent Light bulb

I got these photos simply by holding the little homemade spectrometer up to my phone camera. I have a rather cheap phone camera so the spectra are not as well defined in the images as they are if I look through the spectrometer with eyes only. The really neat thing is that I can upload these images to SpectralWorkbench.org where my spectra are converted into graphs. After calibrating my spectroscope with a fluorescent light, I can compare my spectra against each other and against spectra taken by others. It should be a very useful tool for home spectroscopy.

In the image below, I’m comparing the spectrograph of a white L.E.D. light (white line and color spectrum) with the spectrograph of the same light shining through dark green glass (red line). From this comparison we can deduce the absorption spectrum of the green glass. It shows that the green glass reduces the intensity of the light across the spectrum (i.e. the red line is lower), and it shows that the glass absorbs blue and violet from the L.E.D. (i.e. red line drops at the left side).

Perhaps the most interesting spectrum I saw was that of sodium in the flame of a butane lighter. First I made a sodium chloride solution by stirring ordinary table salt into hot water. Then I dipped a cotton swab into the solution, held it over the flame of a butane lighter, and watched it through my spectroscope. At first all I saw was the full spectrum of the burning butane, but all of a sudden a yellow line much brighter than the rest of the spectrum appeared. The yellow line was the spectral signature of sodium. I’ve done this experiment in chemistry lab, but to see the same results at home with a homemade spectrometer is magical.

Getting the spectrograph of a fluorescent light.

Getting the spectrograph of a fluorescent light.

Categories: Poor Mad Science, Science | Tags: , , , , , | Leave a comment

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