Line Spectra Lab |
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Bright line
spectra from gas emission tubes can be easily captured and analyzed digitally by
placing a diffraction grating over the lens of a digital camera and viewed using
a simple cardboard viewing box. The resulting lines are much larger and brighter than those viewed using simple spectroscopes. The results are also easily projected for class discussion! Method: Using a medium size box (approx. 30cm on a side), cut out a 1 cm by 6 cm rectangle in the upper right corner looking from the back side of the box and make a narrow clean slit with two pieces of index card placed close together over the larger slit (see diagram). Place a fine diffraction grating over the lens (and viewfinder if possible) of the digital camera, taping it into place. The camera should be help at a consistent distance from the slit to produce images that are of a consistent scale. This will aid in the digital analysis of the spectrums produced. A simple adjustable "depth guage" attached using the tripod mount on the camera will give consistent geometry. Drill a series of 1/4" holes in a meter stick spaced 10cm apart, attach using a properly threaded thumbscrew, adjusting the depth to maximize the image results. Dim the lights in the room, orient the gas tubes to vertical and capture a series of test images, making sure that the flash is turned off. Use a straight filament light bulb to obtain a continuous spectrum image that will serve as the baseline for analysis and measurement of the spectral lines and their positions using ImageJ software. Record the number of exposures for each emission tube. ImageJ software is available free and has many useful functions.
Under construction... more soon!
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insert photo showing imageJ screen shots and plots |
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