MODERN PHYSICS (PHY 320) LAB

Absorption and Line Spectra

OBJECT:

        To produce both line and absorption spectra using a variety of sources

EXPERIMENT 1:

For reproducible spectra remember to always scan in the same direction.

1. Place a pinhole in front of a white light source and focus the pinhole's image on the entrance slit.  Perform a  scan to display the continuous spectrum of the white light source utilizing the Science Workshop interface, i.e.  scan from 4000 to 7000 Å at 500 Å/min while recording the intensity data on the computer.  You will have to convert the time axis on the graph to wavelength.       

2. Replace the white light source with a high intensity mercury lamp.  Turn the mercury lamp on and allow it to "warm up" for several minutes while you prepare for the measurements of this part. Mercury has a characteristic spectrum which has several strong lines with visible wavelengths.  Again, scan from 4000 to 7000 Å at 500 Å/min while recording the intensity data on the computer.  

3. By selecting a much narrower scan region and scanning at a much slower speed, one can investigate individual spectral lines and the effects of changing slit widths for this spectrometer.   Single line profiles can be studied using the Green line of mercury at 5461 Å.  The resolution of multiple lines can be studied using the Yellow doublet at 5790 and 5791 Å.

EXPERIMENT 2:

Absorption Spectra will be investigated in this experiment.  Using the dual beam, uv-visible absorption spectrometer, obtain absorption spectra for the following materials:

• Red and green colored plastic filters and compare sharpness of cut-on/cut-off edges.

• Additive (red, green, blue) and subtractive (cyan, magenta, yellow) color filters

• Spectra for individual and combination of ND filters (0.3, 0.6, 0.9) and confirm optical density formula.  The transmission of a filter can be characterized by D, the optical density.  T = 10^-D.

• Bulk absorption in various crystals:
  red = potassium ferricyanide
  green = nickel sulfate
  blue = copper sulfate

Zoom in on regions of interest.  Describe the color of each and use this to explain the absorption spectra.