Physics307L F09:People/Martinez/Balmer Series

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  • For lab this week we conducted the Balmer Series experiment. The basic meaning behind our experiment is that different materials have different characteristic emissions when their electrons are excited. Our principle equipment was a spectrometer, an electric current source, and several glass tubes filled with vapors of various elements. Our procedure followed the outline of Dr. Gold's lab manual. We initially calibrated our spectrometer with the accepted values of mercury vapor, on the first day with the yellow line, and on the second with the green. We then examined the spectrum of hydrogen and deuterium to compare. We tried to take data apart and with altering methods: reading the lines from left to right/ right to left, but generally our values remained within the 1-2nm range that could easily have been caused by the line width. Some interesting effects that we observed were that when we touched the box the intensity of the lines increased significantly - Aram suggested that this was probably due to wiring problems of the equipment that we were possible putting back into place with our touch. The hydrogen spectrum showcased a low intensity blur just after the red line, we assumed this was due to some impurity for the sample. Also I was pretty fascinated by the swirling hyperbolas that formed in the glass tubes on either side of the thin section - Aram suggested this was probably due to the electrical current trying to fill the smaller shape and failing to do so, that effect seems almost hydrodynamic like the Coriolis effect, which I theorize is the case because the "plasma" - ionized gas - that is created in the tube acts with apparent hydrodynamic properties. Comparing the spectra from hydrogen and deuterium, the spectra where within our expected errors for each of them, which we expected because our hypothesis was the electro-optical effect would not be effected by the neutral (electrically) neutron that deuterium addsSJK 01:01, 18 December 2008 (EST)
    01:01, 18 December 2008 (EST)
    You missed the fact that the mass is's just a small effect on the values! But if you had enough precision to measure it (and maybe you were seeing a hint of it in the red), this would reveal very important physics. I think you missed out on a lot of learning by not reading a little more about this. I do appreciate your hypothesis, but it seems like you didn't then go see what other hypotheses are out there (e.g. venturing to wikipedia)
    . We did measure differences between the two, but we assumed this was our own misreading from the variable width of the lines.
  • Wiki page for the notebook.
  • Our data analysis was basically just finding the mean and standard deviations for all the calculated values of the Rydberg constant from our individual measurements of the wavelengths and transition number difference by the equation: R = 1/λ * (1/4 - 1/n^2)^-1. Which differs from our other analysis in its complexity, but we could not assign a least squares fit line to our data, as it was more approximated by a parabola. Essentially the data we are reporting for this experiment is:
R(H) = (1.0941321 +/- .004225)*10^7 m^-1
R(D) = (1.0951129 +/- .003278)*10^7 m^-1

The accepted value for the Rydberg constant is

R = 1.0967758 * 10^7 m^-1

So our data fits with the accepted value within its first value of standard deviation, so that refers to a 68% confidence interval. The difference from the accepted for each of our measured values were respectively:

error(H)= 0.241 %
error(D)= 0.152 %
  • The thing I learned most about was the spectroscope, I knew a little about it in theory, like that the prism separates different wavelengths of light based on the speed of the light through the medium. But I have never used or seen one, and I was really impressed by its accuracy especially for such an old piece of equipment. It would have been really cool if we could have found a sodium tube and found the difference between those two close lines to see the resolving power of our equipment. It was also cool to theorize about the reason quantum mechanically ( or whatever science we were using ) why the hydrogen and deuterium spectrum would be equivalent.
  • I don't have a suggestion per se but one problem that I had was that looking for so long at the spectra especially for the dim lines gave me quite a headache. I don't know how this could be improved, maybe it's just a consequence of being a physicist.