User:Emran M. Qassem/Balmer

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In this lab we measured the Rydberg constant for Hydrogen and Deuterium using a spectrometer and compared them with each other and the accepted value of the Rydberg constant.


To do this we used a spectrometer which we first calibrated with a mercury gas tube and the known wavelengths of the mercury spectral lines. Having the calibration, we used the spectrometer to measure the wavelengths of the spectral lines of Hydrogen and Deuterium. This gave us the data to calculate the Rydberg constant.

During our procedure, we found many spectral lines in our Hydrogen that seemed like they should not have been there. We even marked down a yellow line which was not documented anywhere we looked. It was suggested by our professor Dr. Koch that maybe this source was not really hydrogen, or that maybe the spectrometer had an issue with it.


The Rydberg constants we measured:

R_H=1.10(4)*10^7/m\! for Hydrogen
R_D=1.104(5)*10^7/m\! for Deuterium

The accepted value is:



The accepted value is within one sigma of our measured value. It seems our measurements are good. We did change the 690 wavelength calibration correction from -9 to 2, which I am not too sure about doing. It did give us better data, and might very well have been a mistake in the calibration, but I believe the correct thing to have done in this case is to go back and remeasure instead of changing it to the value which matches the rest and works out well.


In this lab I learned that doing the experiment and writing everything down is more important than getting a good result. Even though we had a few problems with extra spectral lines and in the end we changed one of the calibration parameters, we took note of everything, so that it was documented.

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