Physics307L:People/Cochran/Electron diffraction

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Summary

The purpose of this lab is to attempt to verify the de Broglie hypothesis, as well as to measure the spacing of planes in graphite. Cristhian Carrillo was my lab partner for this lab. We used an electron diffraction tube, aWavetek 85XT digital multimeter, Cabrera precision calipers, and a 3B DC power supply (Model U3310) .
set up
set up
My procedure for this lab is described here.

Procedure/Results

We followed the procedure described in Professor Gold's manual. We switched on the heater and HV power supplies and measured the diameters of the inner and outer rings for voltages from 4kV to 2.5 kV. These values are recorded in my lab notebook. Using a formula derived from the de Broglie hypothesis and a Google spreadsheet, I calculated the graphite lattice spacings for these two diameters , averaged the values, and obtained:

  •  d_{inner} = 0.19524 +/- 0.001 nm\,\!
  •  d_{outer} = 0.11153 +/- 0.0006 nm\,\!

with percent errors of:

  • \% error_{inner} = 8.34 %\,\!
  • \% error_{outer} = 9.33 %\,\!
SJK 22:43, 21 December 2010 (EST)
22:43, 21 December 2010 (EST)Missing is a statistical comparison with the accepted value.  How much does it differ, relative to the size of the SEM?
22:43, 21 December 2010 (EST)
Missing is a statistical comparison with the accepted value. How much does it differ, relative to the size of the SEM?

All this was done using a Google spreadsheet.

Conclusion

Our error for the inner diameter's lattice spacing was lower than that for the outer diameter's spacing, but the standard error of the mean was higher for the inner diameter's lattice spacing than it was for the outer diameter's lattice spacing. The outer diameter was much fuzzier and harder to measure, and this may have contributed to its higher percent error. I was also unsure of whether our beam was directed exactly at the center of the bulb - measuring this and making some sort of mark might have helped eliminate some error when it came time to correct for the curvature of the bulb.

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