Physics307L:People/Cochran/Electron diffraction
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) . 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:
- Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://api.formulasearchengine.com/v1/":): {\displaystyle d_{inner} = 0.19524 +/- 0.001 nm\,\! }
- Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://api.formulasearchengine.com/v1/":): {\displaystyle d_{outer} = 0.11153 +/- 0.0006 nm\,\! }
with percent errors of:
- Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://api.formulasearchengine.com/v1/":): {\displaystyle \% error_{inner} = 8.34 %\,\! }
- Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://api.formulasearchengine.com/v1/":): {\displaystyle \% error_{outer} = 9.33 %\,\! }
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.