Physics307L:People/Mondragon/Notebook/071121

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calibration

SJK 21:45, 1 December 2007 (CST)
21:45, 1 December 2007 (CST)You missed the fact that you were supposed to rotate the prism to correct for this mis-calibration!  Your data would be much better in that case.  (These methods may be appropriate after you've rotated the prism to the best of your abilities.  (Also, did you account for the backlash?)
21:45, 1 December 2007 (CST)
You missed the fact that you were supposed to rotate the prism to correct for this mis-calibration! Your data would be much better in that case. (These methods may be appropriate after you've rotated the prism to the best of your abilities. (Also, did you account for the backlash?)

using mercury to calibrate. center of slit, measuring clockwise

calibration data
coloractual wavelengthmeasured wavelength
red690.75nm634nm
yellow579nm545nm
yellow577nm542nm
green546.1nm525nm
violet435.8nm422nm

so the calibration curve is real\,wavelength=1.204205321\times measured\,value-76.8339591

the hydrogen spectrum

SJK 21:49, 1 December 2007 (CST)
21:49, 1 December 2007 (CST)Did you really only take one measurement for each color?  (After calibrating correctly (above)), you need to take many "independent" measurements at each color to minimize uncertainty.
21:49, 1 December 2007 (CST)
Did you really only take one measurement for each color? (After calibrating correctly (above)), you need to take many "independent" measurements at each color to minimize uncertainty.
hydrogen spectum measurements and rough calculations
colorMeasured ValueActual Wavelength (nm)Actual Wavelength (m)1/wavelengthn2 − 2n − 2Rydberg Constant
red 604 650.5060546 6.50506E-07 1537264.708 3 0.138888889 1.1068306E+07
blue green 466.5 484.927823 4.84928E-07 2062162.558 4 0.1875 1.0998200E+07
violet 421 430.1364809 4.30136E-07 2324843.496 5 0.21 1.1070683E+07
faint violet 400.2 405.0890102 4.05089E-07 2468593.259 6 0.222222222 1.1108670E+07

mean value for Rydberg constant=1.1061*10^{7}\,\mathrm{m}^{-1} standard deviation 4.6*10^{4}\,\mathrm{m}^{-1}

CALCULATIONS

heres the excel file Image:L and T Balmer series.xlsx Section above has numbers from the excel file.

here is a more careful analysis

Linefit says the calibration data fits the line actual\,wavelength=(1.204205 \pm 0.042636)*measured\,wavelength-(76.833959 \pm 22.932003)nm Image:HgCalibration curve.png

Error propagation

No data on measurement error was ever taken, so, for any measurement of wavelength the error on the calculated actual value will be

actual\,wavelength\,error=0.042636*measured\,wavelength+22.932003nm

The calculated Rydberg constant is related to the measured wavelength value thusly

\begin{align}
  \frac{1}{\lambda} &=  R_\mathrm{H}\left(\frac{1}{2^2} - \frac{1}{n^2}\right), n=3,4,5,...\\
  R_\mathrm{H}      &=  \frac{1}{\left(\frac{1}{2^2} - \frac{1}{n^2}\right)\lambda}\\
  R_\mathrm{H}      &=  \frac{1}{\left(\frac{1}{2^2} - \frac{1}{n^2}\right)(m*\lambda_m+b)}\\
\end{align}
Where λm is the wavelength measured by the instrument, m is the slope of the calibration curve, and b is the y intercept of the curve. Because of the uncertainty in the fit, the calculated value of the Rydberg constant will have uncertainty.

\Delta R_\mathrm{H} =  \frac{1}{\left(\frac{1}{2^2} - \frac{1}{n^2}\right)(m*\lambda_m+b)^2}(\Delta m*\lambda_m+\Delta b)= R_\mathrm{H} \frac{\Delta m*\lambda_m+\Delta b}{m*\lambda_m+b}=R_\mathrm{H} \frac{\Delta \lambda}{\lambda}
The uncertiainty in RH is just RH times the relative uncertainty in the calculated wavelength.

hydrogen spectum measurements and rough calculations
colornAccepted Wavelength (nm)Measured ValueCalulated Actual Wavelength (nm)Calculated Error(nm)Relative ErrorActual Wavelength (m)Rydberg ConstantRydberg uncertainty
red 3656604 650.506 48.6840.0748406.50506E-07 1.10683E+078.284E+05
blue green 4486466.5 484.928 44.8220.0883054.84928E-07 1.09982E+079.712E+05
violet 5434421 430.136 40.8820.0950444.30136E-07 1.10707E+071.0522E+06
faint violet 6410400.2 405.089 39.9940.0987314.05089E-07 1.11087E+071.0968E+06

Average for Rydberg constant=  1.10592*10^7\,\mathrm{m}^{-1}. Uncertainty of average = 9.64*10^5\,\mathrm{m}^{-1}. Accepted value = 10 967 758.341 \pm 0.001\,\mathrm{m}^{-1}

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