our experiment. Therefore, we can determine the grating spacing of a diffraction grating using the grating spectrometer and a helium discharge tube. For part B and part C, we were successful to calculate each wavelength for a particular color spectral line of unknown gas and to compare with the emission spectral charts in order to identify the “unknown” gas, which is Hydrogen gas. Although we haven’t found the blue color of spectral line for our “unknown” gas tube during this experiment, the other 3 colors of spectral lines have all seen from the grating spectrometer. Also, the above calculation has shown that the difference between the wavelength for each spectral line of our unknown gas and the wavelength for each spectral line of Hydrogen gas do agree within their uncertainties expect the values of violet spectral line. However, since the difference of the wavelengths for greenish-blue and red spectral lines are very close each other, we can bravely identify that our “unknown” gas is Hydrogen gas. In this particular experiment, the measurements that affected our precision the most were the positions at left angular, which it’s 0.03%. The measurements of the positions at left angular and their uncertainties were obtained from a spectrometer. Since the spectrometer manufacturer has provided an instrument uncertainty for its Vernier scales which was quite accurate to measure an angle in degree, we could not do much about it to decrease this uncertainty propagation. To improve this, we would suggest to measure the 2 nd -order or 3 rd -order spectra (one on each side of the central maximum) in order to get a larger angles for the positions of left angular _L. This would increase our measurements of position of _L, and in turn, reduce the fractional uncertainty δ[ _L]/( _L) and thus improve our precision.
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