User:David K. O'Hara/Notebook/physics 307 lab/electron diffraction lab summary
Electron Diffraction Lab Summary
SJK 17:33, 11 October 2009 (EDT)
This experiment's main intent was to demonstrate that electrons have the property of waves, by the interaction of an electron with a small slit and observing the diffraction patterns that result. In this experiment the role of small slit is played by a graphite screen, if we had been able to use a single graphite crystal and passed a single electron through it, we would have had a point diffraction pattern. With the setup we have, to insure bragg diffraction occurs, they use a graphite screen which has multiple lattice structures that the incoming electrons can interface with. []
All pertinent notes are located in the lab notebook for this experiment. []
SJK 17:23, 11 October 2009 (EDT)
Outer maxima results
Actual atomic spacing = .213nm
slope of outer diameter vs 1/sqrt(v) = .581625 m/sqrt(V)
Atomic spacing calculated from slope = .328nm
percent error = 32% error from accepted value
Inner maxima results
Actual atomic spacing = .123nm
slope of outer diameter vs 1/sqrt(v) = .389401 m/sqrt(V)
Atomic spacing calculated from slope = .219nm
percent error = 43% error from expected value
SJK Steve Koch 17:27, 11 October 2009 (EDT)
The difficulties in measurement for this experiment were substantial, the choice of where to take the measurement off the ring (either inner or outer), the visual difficulty of getting an accurate width on the vernier calipers and the idea that you are sort of ballparking the voltage reading using an analog meter which did not have a ton of precision in its readout.
The error between the true value and the calculated value I came up with is mostly due to the fact that the rings are extremely difficult to see. This creates an error that makes all the calculations and conclusions drawn from them suspect.
These difficulties aside, the experiment does a superb job of reaching the goals of verifying / demonstrating the wave aspect of the electron. The diffraction rings are generated by the multiple diffractions that occur due to the countless electron-lattice interactions as the electron beam is fired at the graphite screen.