User:David J Weiss/Notebook/people/weiss/eDiffraction

From OpenWetWare
Jump to: navigation, search

Summary of the Electron Diffraction Lab

SJK Incomplete Feedback Notice
Incomplete Feedback Notice
My feedback is incomplete on this page for two reasons. First, the value of the feedback to the students is low, given that the course is over. Second, I'm running out of time to finish grading!
  • The main goal of this lab was to determine the diffraction pattern that electrons create going through a diffraction grating in our case this was graphite. In our case we were able to see two different diffraction patterns and able to measure the radii of those and with some math-magic able to determine the value for the spacing of those and compare it to the expected values.
  • For my two trials I obtained 2 sets of results for the inner and outer diameters of the diffraction gratings
The first set was off by a significant amount on both the inner and outer diameters. The value I obtained for the inner diameter was .09355 nm which had an error of 56.1%. For the inner diameter I obtained a value of .1933 nm which had an error of 58%. So both measurements were off by 50% which is cool in that I was making the same mistakes on both sets of measurements so that they had an error in the same ball park. This could be due to the fact that the voltages were off or I was taking bad measurements and they were constantly off by approximately the same amount but this does not seem likely but it could be. My guess is that I did not have my rings centered on the bulb and that the readings were thrown off by approximately the same amount for every data point that I took. So in the future I need to take more care in the initial set up of my equipment and make sure that every thing is set up properly before i start taking measurements.
The second set of data that I collected was better in terms of the error but not as good looking at the spread on the error. The inner diameter was 0.189 nm which error was 11.26%. The outer diameter was 0.125 nm and had an error of 1.55%. The spread on the error was not as good on these data points but the data was better in terms of error compared to the expected values. This could be due to numerous reasons. I suspect that I was just not taking good data on the inner diameter but I cannot see why I would get better reading on one compared to the other when I was taking the inner then the outer then going down in voltage so I am a little confused in why the errors differ that much in the same experiment.
  • Conclusions: The conclusions that I can draw from this lab are that the first set of data was a good one with a large amount of systematic error in the form of misalignment of the rings before any data was collected. As for the second day of data taking I cannot pin down the reason's for the differences in the error. This could be from random error but that doesn't seem likely and the cause is likely just systematic error in taking the inner diameter reading's probably not properly taking the measurements on the round bulb and not aligning the calipers correctly. The 1% error comes from random errors in the calipers and in the voltage that was being displayed on the high voltage display but I am comfortable with this error.