In this Lab, I worked with David Weiss, with many thanks for his help. We started by learning some of the elementary set-up of the spectrometer and its parts, the adjustment of the prism, its original setting on a known spectral wavelength, and then the use of the calibrated knob to take readings of other spectral lines. We spoke with Professor Koch and Pranav Rathi about safety concerns, especially with regards to the vapor lamp which carries 5000 volts.
We set up the spectroscope to align with the vapor lamp such that the slit to allow in the light was at the center of the vapor tube. We chose to calibrate based on the central green line of the Mercury vapor tube at 546.1 nm, and adjusted the prism until this line met the cross hairs when the calibrated dial was set at that reading. We then measured the other known spectral lines to assess the accuracy of the scale and the systemic considerations for the readings of Hydrogen and deuterium.
On day one we practiced centering the spectral lines and reading the scale on the spectrometer, taking readings on both hydrogen and deuterium. At this time, I was observing the lines and taking the readings and David was recording the data and writing the notes.
On day two, David was setting the spectral lines, and I was reading the scale. We took multiple readings for each spectral line in both the hydrogen and the deuterium in order to determine the error. It was informative to see how much the multiple readings varied for the same set up taken in series. We moved off the line and took the readings from the same direction each time to minimize the error from the play in the adjustment knob.
Unfortunately my notes were lost both days, but I was able to copy the data from David's notes.
EquipmentSJK 16:52, 29 September 2009 (EDT)
- Constant-Deviation Spectrometer[]
- Spectrum Tube Power Supply Model SP200 5000V
- Spectrum Tube, Mercury Vapor S-68755-30-K
- Spectrum Tube, Hydrogen S-68755-30-G
- Spectrum Tube, Deuteruim S-68755-30-E
- Electrical Shock: The main safety concern of this lab is with respect to the Vapor Lamp which operates on 5000 volts, enough to cause serios injury.
- Breakage: The glass vapor tubes are fragile and can break, possibly causing cuts. Also the spectrometer needs to be treated with care to keep it working well and to avoid damaging the prism.
- Toxicity: The Mercury Vapor Tube contains toxic gas that can cause harm if inhaled, so it is especially important to take care with that tube.
We set up the spectrometer on the desk between two computers and set the vapor lamp on books until it was to a height where the center of the vapor tube was at the level of the slit that received the light into the spectrometer.
SJK 01:57, 29 September 2009 (EDT)
We put the mercury vapor tube into the lamp, turned it on, and moved the prism until the green spectral line was at the cross-hairs when the guage was set at 546.1 nm. We found the other spectral lines for Mercury Vapor as follows.
Calibration for day one:
- Red...........701.0 nm
- Yellow1.......578.5 nm
- Yellow2.......576.4 nm
- Green.........546.1 nm ~ the calibration line
- Violet1.......404.5 nm
- Violet2.......435.9 nm
Calibration for day two:
- Red...........697.0 nm
- Yellow1.......579.7 nm
- Yellow2.......577.0 nm
- Green.........546.1 nm ~ the calibration line
- Violet2.......435.9 nm
Data Day One
Notes from David:
After we calibrated the Spectrometer, we then measured the spectral lines of the Hydrogen gas below. The first line we observed was the violet line followed by the blue-green line, then the red. We were a little confused about what the actual spectral lines were, but we decided upon two in the range of yellow spectral lines.
We then measured the Deuterium. The first spectral line we observed was the red line, followed by the violet line, then the blue-green line. A yellow line was observed followed by an orange line, but both of them were more faint than the others.
- Hydrogen Vapor Spectral Lines:
- Deuterium Vapor Spectral Lines:
Data Day Two
- Hydrogen Vapor Spectral Lines
Red: 657.6nm, 657.0nm, 657.6nm, 577.7nm, 657.4nm
Orange: 603.3nm, 604.0nm, 603.9nm, 603.7nm, 603.6nm
Yellow: 582.4nm, 582.7nm, 582.6nm, 582.9nm, 582.4nm
Blue-Green: 486.3nm, 486.0nm, 486.2nm, 485.9nm, 485.9nm
Viloet: 433.8nm, 434nm, 433.9nm, 434.2nm, 434.3nm
- Deuterium Vapor Spectral Lines
Red: 657.8nm, 656.7nm, 657.2nm, 658.2nm, 656.6nm
Blue-Green: 485.2nm, 485.6nm, 485.2, 485.2nm, 485.2nm
My thanks to David Weiss for setting up the data analysis.
Violet: 434.05nm+/-.07nmSJK 02:02, 29 September 2009 (EDT)
Calculating the Rhydberg Constant
Rydberg formula for hydrogen:
Using this formula(from Wikipedia) you can calculate the approximate value for the Rydberg Constant by knowing the transitions from the excited levels to the non excited states(ground states) by the following calculations:
where RH is the Rydberg Constant for hydrogen, λ is the observed wavelength, and n is the excited energy state that the electron was in. You can find out what states that the electron was in by looking that up on a table. David used the Wiki page on Balmer Series Wiki Article and looked at the lines for the Balmer series.
The n=5 line represents the violet color that is emitted, the n=4 line represents the blue-green line that is emitted. The n=3 represents the red line that is emitted.
SJK 02:08, 29 September 2009 (EDT)
Rydberg Constant for Hydrogen(RH)
- = RH for the red spectral line = 1.0944245+/-.00071 * 107m − 1
- = RH for the blue-green spectral line = 1.0972808+/-.000158005 * 107m − 1
- = RH for the violet spectral line = 1.0979866+/-.0001769 * 107m − 1
Rydberg Constant for Deuterium(RD)
- = RD for the red spectral line = 1.0899183+/-.00507 * 107m − 1
- = RD for the blue-green spectral line = 0.910980157+/-.00028 * 107m − 1
Note: Due to a typo, this was miscalculated. Using the proper averaged measurement for the wavelength, 485.54nm, the Rhydberg constant is found to be 1.0986370 * 107m − 1
- = RD for the violet spectral line = 1.09645516 * 107m − 1(no +/- due to only seeing the two spectral lines and having only one data point)
Concerns and Sources of ErrorSJK 02:10, 29 September 2009 (EDT)
- Systematic Error: When we first calibrated the spectrometer, we noticed that we had not fully tightened the set screw on the prism, so there was some slippage of the prism as we moved through the range of our measurements. As a result we repeated the first calibration with the prism set properly. However, this may still be a concern on a small scale.
In addition, the scale on the dial to the wavelengths was difficult to read and did not have as much accuracy for the longer wavelengths. The dial had a significant amount of play in the gears as well, which we tried to minimize by always taking the readings from the same direction.
- Random Error: This could come from reading the markings or aligning the spectral lines slightly differently for each repitition of a data point, even though they were all taken from the same direction.
- The one outlier reading for the Deuterium red spectral line on day two may have been due to inaccurate reading of the scale markings or due to approaching the spectral line from the opposite direction, leading to error from the play in the adjustment gears. In addition, I did not know how to include the error of our readings for Mercury from its standard spectral line values into our data collected for Hydrogen and Deuterium It seems we should have adjusted our readings due to the amount that the Mercury readings varied across the scale. In doing future labs, I would work on developing this correction to obtain more accurate results with other calibrations.
- Another concern comes from the fact that we observed five spectral lines for Hydrogen, two of them yellow, whereas in the lab notes and other information thaat I've read there are only four listed, two of them violet. So it may be that our vapor tube was contaminated with another element. Although we still found the Rhydberg Constant within a small degree of error, this seems a major issue of uncertainty.