Exercise

  1. Describe the spectrum of the low pressure sodium lamp as viewed through your spectral glasses. 
     
  2. At what wavelength is the spectral line observed in the low pressure sodium lamp?
     
  3. Describe the spectrum of the high pressure sodium lamp as viewed with your spectral glasses.
     
  4. What kind of feature do you observe at the location of the sodium line from question 2?  How does the wavelength of this feature compare to that of the sodium emission line?
     
  5. Would you expect to see absorption or emission from a star? Explain your reasoning.
Bohr model
Bohr Mode Image Credit: "Bohr-atom-PAR" by JabberWok at the English language Wikipedia. Licensed under CC BY-SA 3.0 via Commons

 

 

The spectra you have been observing is due to the gas being heated and are examples of emission line spectra. This process can also occur in reverse, with light of the line’s wavelength being captured by the atom in a process known as absorption.  Absorption occurs anytime a cooler, thin gas is located in front of a white light source. 

Your TA will have two light sources at the front of the room, a low pressure sodium lamp and a high pressure sodium lamp.  You will view these lamps with your spectral glasses as well as with the ocean optics spectrometer.