When we studied light we learned about three different kinds of spectra that astronomers might see from a star. If we are looking at a black body (and stars act very much like black bodies) we will see a continuous spectrum. If a star is surrounded by a shell of cooler gas and dust, we may see an absorption spectrum. Looking at the sun we see what are called Fraunhofer Lines, bthe absence of certain colors that have been absorbed by the atmosphere of the sun. Similarly, under the right conditions we can also see an Emmission Spectra, where bright lines are emmitted by certain elements. Basically, the gases are stimulated so that the electrons go up to higher energy levels and bright lines indicate the energy of photons given off when the electrons return to lower energy states. Your job is to use a spectroscope to examine these different spectra.

    You need to hold the spectrometer correctly. Your instructor will show you how to hold the instrument. If you look at an incandescent bulb you should see a continuous spectrum. It makes light by glowing hot. It looks something like the following:

    Be sure to aim the slit (on the right side of the spectrometer) at the bulb rather than trying to look directly at the bulb. Look at the spectrum on the scale. Draw below what you see and describe it so someone not in this course would know what you saw and why:
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

    What ranges did the spectrum extend over in wavelength?
 

2.  Now point thhe instrument at a flourescent lamp. Below is a picture of a hydrogen emission spectrum. Its lines are different than what you see. Why?
 
 

What kind of gas do you suppose is in the flourescent tube? Check this out with the spectrum chart on the blackboard in the lab. (You actually will probably see a continuous spectrum with emission lines imposed on it.) We are interested in what element causes these bright lines.
 
 
 

3. Look at the spectrum tube set up by your instructor. Record the values of the light emission lines. Check this out against the spectrum chart on the wall by the blackboard. Can you tell what element this is?
 
 
 

4. Check out the spectra of several different light sources.The street lamps, campus lights, neon lights, if they are available, are good sources. See if you can find some absorption lines in a spectra. What caused them?
 
 
 
 
 
 
 
 
 
 
 
 
 

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