Emission Spectra

The lab for this week is truly a discovery exercise.  In fact, I direct you
to a site at the Exploritorium in San Francisco for information
(http://www.exploratorium.edu/spectroscope/)

The idea is to use the diffraction grating I included in the supplemental
lab packet (the thing that looks like 35 mm slide), follow the instructions
on the exploritorium site, and build a spectroscope in a shoebox.  Then take
your device out and look at some light sources and draw what you see.  You
will want to do your drawing in color and then use the spectrum I included
here in the notes section to get an idea of which wavelengths corresponds to the
various colors.  The exploritorium site makes some suggestions as to what to
look at, but here are some also:

1.  A white street lamp is a Mercury vapor lamp.  Now for reasons that have
more to do with politics than science, they usually coat the inside of the
lamp with fluorescent dyes that give a continuous spectrum.  But if you look
closely, you can see the Mercury emission lines superimposed onto the
continuum.  A fluorescent lamp in your house gives the same spectrum.

2.  An incandescent lamp gives a continuous spectrum

3.  A yellow street light is a sodium vapor lamp.  Same comments as above
for the mercury lamp.

4.  Orange-red beer signs are Neon vapor lamps.  You should see a "forest"
of lines in the orange-red part of the spectrum.  Caution - only orange-red
signs are Neon - others are white lights wrapped in colored plastic.

5.  If you catch a glare spot off a car bumper (for example) and narrow your
slit down, you may be able to see the absorption spectrum of the Sun.

Make sure the slit on the spectroscope is very narrow for any of these
sources.  You can make a useable slit out of index cards cut very cleanly.
I used to make the slit out of a double edged razor blade cut in half, with
the edges facing each other.  The two edges of the slit want to be almost
touching to observe the spectra.  Even narrower for the Sun.  Using a narrow
slits makes the emission lines easier to see, but there is a trade off here.
Narrower slits give better (sharper) spectra, but admit less light.

If you get bothered by the police during your observations, I don't know
you.