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Re: Absorbtion spectra



Start from the other premise. How would a spectometer lab work if the
emission lines couldn't be seen? The light enters the collimator tube,
through the prism/grating and then enters the telescope. We see the
emission spectrum, and can calculate the wavelength of each "line" via
"simple" formulae.

The question I always pose to my students is: What governs the size of
the "lines" we see in the spectrum? Since they have to align the
equipment, they always answer that it is the collimator slit. The more
narrow the slit, the better accuracy of their measurements, up to a
point. However, there is a point of diminishing returns. If you make
the slit too narrow, you lose intensity and you get some fringing about
the slit opening.

I don't know if that helps, but I hope it does.

Peter Schoch

GARY HEMMINGER wrote:

A student has asked the following question which seems like a good
one to me:
If the black lines in an absorbtion spectra correspond to
individual wavelengths, then shouldn't they be too thin to be seen?
Any thoughts? Do they have a "width"?

*****************************************
Gary Hemminger
Dwight-Engelwood School
315 E. Palisade Ave.
Englewood, New Jersey
07631
e-mail: hemmig@d-e.org
*******************************************