Physics307L F09:Winter Break Lab Fest/Balmer

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This is a spectrometer from the 1800's that the 307L TA, Aram Gragossian saw at the Smithsonian this week. Pretty similar to our ultra-modern one, right?

In this lab, you use a prism spectrometer to analyze the spectrum of atomic hydrogen. The spectrometer allows you to measure the wavelengths of the spectral lines that the excited hydrogen gas emits. (See this link for hydrogen spectrum:

General procedure

  1. Discuss safety first!
  2. "Calibrate" the spectrometer using the mercury bulb. You do this by rotating the prism to make the known wavelengths of Mercury match (so it's a little bit of a circular kind of argument)
    • Make sure to learn about and understand gear backlash or "slop"
  3. Measure the wavelengths of the hydrogen lines
    • Be careful of gear backlash
  4. Use the data and the Balmer formula to find the value of the Rydberg constant RH
    • We'll set you up with an Excel sheet to show you how to do the linear regression
    • You'll be surprised at how precisely you can measure this very important physical constant!