Physics307L:People/Cordova/Matt's Electron Diffraction Summary
My Partner for this lab was Sebastian.
The notebook for this lab can be found here.
Steve Koch 22:17, 21 December 2010 (EST): Good work on this lab. Good discussion of systematic error and using SEM to compare with accepted values.
Purpose
The purpose of this lab is to recognize the behavior of electrons as that of a wave, While also be studying the de Broglie hypothesis [math]\displaystyle{ \lambda=h/p }[/math]. We will be observing this through the measurement of the diffraction pattern obtained by sending a beam of [math]\displaystyle{ e^- }[/math] through a diffraction grating (in this case a thin layer of graphite).
Safety
- A high voltage source will be in use. Also, this lab is set up on a metallic surface. Do not have any unnecessary objects around this voltage source.
- This lab is done primarily in a dark room. Be aware of your surroundings.
- The thin graphite can be punctured by an intense current, so it is suggested to keep this monitored.
Equipment
- Calipers - Carrec Precision 6" Digital Caliper
- TEL Universal Stand
- Electron Diffraction Tube - Tel 2555
- 3B DC Power Supply 0-5kV - Model: 433010
- Hewlett Packard Power Supply - 6216B
Set Up
A detailed set up can be found in Prof. Gold's lab manual. We opted to not include the current meter in the set up, as reaching dangerous levels is very unlikely and the lab suggests to visually inspect the layer of graphite for overheating anyways.
Results
[math]\displaystyle{ d_{inner,outer}=.1889(5)nm }[/math] is 11.3% off.
[math]\displaystyle{ d_{outer,outer}=.1101(4)nm }[/math] is 10.5% off.
[math]\displaystyle{ d_{inner,inner}=.2071(4)nm }[/math] is 2.8% off.
[math]\displaystyle{ d_{outer,inner}=.1178{3}nm }[/math] is 4.2% off.
While our values are relatively close to the accepted value of .123nm and .213nm, all of our values are several SEM away from the accepted values. There, as always, is some systematic error in our lab. Contributing factors may include the following:
- The process of measuring the rings on a spherical surface using a caliber is an awkward thing to do. There is clearly human error in this process.
- The lab stated L is equal to 13 +/- .2 cm. I neglected this fact. I strictly used the value L = 13cm. Could have been accounted for, but I neglected to do so.
- We are measuring the pattern created by diffracted electrons using a metal caliber. I see no way how this could not affect the data.
