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Spectrometry Lab
Introduction
A bright-line spectrum is produced by hot gases of low density. The spectrum which results has
bright lines separated by dark spaces. The bright lines are determined by the kinds of atoms present in
the gases and the amount of energy supplied. Each gas emits its own bright-line spectrum.
Stars, like our own sun, emit dark-line spectra. A dark-line spectrum, however, can only be
directly examined by a more sophisticated spectroscope. A dark-line spectrum is produced when a
cooler gas is in front of the source of a continuous spectrum. The cooler gas absorbs light energy from
the parts of the spectrum where, if heated, it would emit bright lines. The spectrum is broken by dark
spaces, which are determined by the number and kinds of gases through which it passes. The dark-line
spectrum of a star occurs when the continuous spectrum of the underlying layers of the star is partially
absorbed by the cooler outer layers.
The sun will appear as a continuous spectrum. In reality, however, there are small, dark
absorption lines that cannot be distinguished.
Materials
 Spectroscope
 Colored Pencils
Procedure
1. Examine the fluorescent lights (the classroom lights) with your spectroscope. Sketch the brightline spectrum below.
2. Examine the incandescent light bulb with your spectroscope. Sketch the spectrum below.
3. Examine the mercury light with your spectroscope. Sketch the bright-line spectrum below.
4. Examine the black light (UV light) with your spectroscope. Sketch the spectrum below.
5. Examine the spectrum of the sun with your spectroscope. Sketch the solar spectrum below.
WARNING: DO NOT POINT YOUR SPECTROSCOPE DIRECTLY AT THE SUN!!!
Point your spectroscope off to the side of the sun.
Conclusions
1. Name the order of colors in the continuous spectrum, from shortest wavelength to longest.
2. How is the spectrum of the incandescent light bulb different from the fluorescent light’s
spectrum?
3. Describe the bright-line spectrum of mercury light.
4. Describe the spectrum of a UV light.
5. How are bright-line spectra a valuable tool to chemists?
6. What do the dark lines in the dark-line spectra of stars indicate?
7. How do these dark lines help determine the composition of stars?
8. Which type of dark-line spectra represents the hottest star, one with many dark lines or one with
few? Why?