The purpose of this lab is to observe and classify spectra lines of the hydrogen and deuterium atoms. By using electrical stimulation to excite our atoms to higher energy levels we can measure the emitted photons of wavelengths equivalent to the energy of our excited electrons. Through this lab and our measurements we should also be able to experimentally determine Rydberg's constant, R, that is used in the equation for hydrogen:
To begin the experiment the following preliminary steps were taken
Make sure that no parallax exists between the cross-hairs and the slit of the spectrometer when we focus it sharply. This is done by adjusting the spectrometer by bringing the cross-hairs into focus and sliding the ocular to a position that suits our vision.
Bring the slit into focus by turning the large ring near the center of the viewing telescope
Attach and position the mercury bulb into the spectrum tube power supply.
Turn on the spectrum tube power supply and allow time(about 5 minutes) for the mercury bulb to warm up.
Calibrate the spectrometer by using a wide slit setting to find a line of the mercury spectrum and narrow the slit until the line comes into sharp focus.
Locate all mercury spectra lines and note the position or the value of your spectrometer dial.
Use known values of light wavelengths to finish calibrating your system.
Use data to correspond the wavelengths with the correct quantum numbers.
Use our equation to solve for Rydberg's constant, R, in each case.
Repeat this process for deuterium.
Measurements and Data
The following table was taken from Professor Gold's Manual, pg 29 and the values were used to calibrate our spectrometer using the mercury bulb.
Color
Wavelength (nm)
Deep Violet (very hard to see)
404.7
Violet
435.8
Very Weak Blue-Green
skip this one
Green
546.1
Yellow 1
577.0
Yellow 2
579.0
Red
690.75
The following tables are the data we took during lab using our calibrated spectroscope:
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Calculations and Analysis
Using our raw data tables we were able to use standard function in excel to calculate our mean, standard deviation and standard error margins for each spectra line. Here you can see our final data results:
-To avoid gear backlash (where we turn the measurement knob but the gears don't shift due to a small "empty space") we made sure to turn our knob at least a full turn behind our spectra line and then slowly turned the knob to our measurement.
-Due to the fact that we did this experiment over the course of two non-consecutive days, we need to take into account that we had to recalibrate the spectroscope before resuming experimentation on the second day.
Summary
If you wish to see my informal summary of this lab follow this link
Acknowledgments
Please note that Anastasia Ierides was my lab partner for this lab. Her version of this lab can be found here
Prof. Gold's Lab Manual served as a loose guideline for our lab procedure and our calibration wave lengths
We used Google Docs to format and post our raw data and error analysis to our wiki notebook
Our accepted values for the Balmer Series came from hyperphysics.com
Wikipedia had a great article on the Balmer Series and we used it to confirm our results and understanding for this lab