Ludwik Kowalski asked about how to see a spectrum from white light using a
CD. I was intrigued, so I went into the lab and tried it. It does work. My
guess is that it needs a fairly narrow slit. Here was my set-up.
Light source - PASCO light source from its optics benches turned upside
down on the lab table with the hole in the back side (for a white light
source) located three cm above the edge of the CD and angled so as to
"reflect off of the opposite side of the hole in the middle of the CD.
Screen - black, faded poster paper held about 20 cm from the other edge of
CD showed the zero order image a few centimeters up from the bottom, the
first order spectrum was located about 15-20 cm up, and the second order
spectrum was also visible but very dim; moving the scree closed to the CD
showed the second order spectrum more clearly.
Image - the image had a very pronounced narrow "spike" which was the
spectrum from the narrow incandescent filament, but it also showed very
broad curved shoulders coming from reflections and scattered light from
other parts of the bulb and light source. (Using actual slits should clean
up the image but the intensity of the spectra will also decrease.)
Neat idea!
Richard
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Dr. Richard L. Bowman
Chair, Dept. of Physics e-mail: rbowman@bridgewater.edu
(and Dir. of Academic Computing) phone: 540-828-5441
Bridgewater College FAX: 540-828-5479
Bridgewater, VA 22812 http://www.bridgewater.edu/~rbowman/
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