User:Chad A McCoy/Notebook/Jr. Lab/2008/09/29

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SJK 02:06, 19 October 2008 (EDT)
02:06, 19 October 2008 (EDT)Very good primary lab notebook.  Seems like you have all the critical information, and in addition lots of important observations and details about your methods
02:06, 19 October 2008 (EDT)
Very good primary lab notebook. Seems like you have all the critical information, and in addition lots of important observations and details about your methods

Electron Diffraction Lab: 9/29/2008

  • For the electron diffraction lab, I am using a Teltron Limited 813 kV power Unit, a Hewlett Packard model 6216B Power Supply, a Teltron 2501 universal stand and a Teltron 2555 electron diffraction tube.
  • I am also using a WaveTek Meterman 85XT digital multimeter, set to 2mA DC, such that I am able to monitor the amperage and ensure that it does not exceed .25mA, as that value would destroy the graphite layer that acts as the diffraction grating.
  • The set-up of the experiment had a high voltage power supply connected to the anode of the diffraction tube, with the heater of the tube connected to the fixed voltage setting on the supply.
  • The detailed procedure and background information can be found in section 3 of Professor Gold's Lab manual, which is located here
  • All measurements taken using calipers accurate to .001 inches, measured from the outside of one edge to the inside of the other to approximate a center to center measurement.
  • For 5kV bias voltage for odd measurements is 10V and for even measurements is 5V.
  • For 4.5kV bias voltage for odd measurements is 5V and for even measurements is 2.5V.
  • For 4kV bias voltage for odd measurements is 2.5V and for even measurements is 0V.
  • For 3.5kV bias voltage for odd measurements is 1V and for even measurements is 0V.
  • For 3kV bias voltage for all measurements is 0V, due to the inability to see the rings with any applied bias voltage.
  • Measurements are done as small ring, then large ring, then adjusting the bias voltage and primary voltage.
SJK 02:01, 19 October 2008 (EDT)
02:01, 19 October 2008 (EDT)These data look great!  Must have taken a long time, but w/ 10 independent measurements, will allow you to really get a hold on your uncertainty in measuring
02:01, 19 October 2008 (EDT)
These data look great! Must have taken a long time, but w/ 10 independent measurements, will allow you to really get a hold on your uncertainty in measuring
Ring Diameter (inches) for Anode Voltage
5 kiloVolts 4.5 kiloVolts 4 kiloVolts 3.5 kiloVolts 3 kiloVolts
Trial # Ring 1 Ring 2 Ring 1 Ring 2 Ring 1 Ring 2 Ring 1 Ring 2 Ring 1 Ring 2
1 0.839 1.576 0.945 1.662 0.966 1.780 1.023 1.944 1.181 2.064
2 0.856 1.559 0.909 1.651 0.976 1.753 1.044 1.960 1.133 2.022
3 0.882 1.580 0.922 1.681 0.946 1.778 1.059 1.963 1.173 2.021
4 0.895 1.575 0.928 1.652 0.942 1.784 1.063 1.976 1.127 2.031
5 0.898 1.586 0.960 1.655 0.973 1.736 1.024 1.941 1.156 2.051
6 0.859 1.595 0.913 1.659 0.984 1.748 1.021 1.938 1.128 2.061
7 0.863 1.572 0.891 1.664 0.988 1.759 1.022 1.956 1.161 2.054
8 0.886 1.582 0.915 1.662 0.942 1.781 1.039 1.941 1.131 2.064
9 0.884 1.580 0.922 1.661 0.981 1.755 1.052 1.936 1.121 2.072
10 0.871 1.599 0.914 1.662 0.939 1.766 1.026 1.947 1.101 2.003
  • Raising the bias voltage increases the voltage on the power supply by approximately an order of ten relative to the bias, such that changing the bias voltage by 10 volts raised the overall voltage by around 100 volts.(Steve Koch:I wonder why this is? Maybe the next group can show me.)
  • The amperage appears to be inversely proportional to the bias voltage and directly proportional to the primary voltage.
  • The maximum amperage as measured by the multimeter was .1074 mA, which was accessed with the power supply set to 5kV and the bias supply set at zero. This was found on the first day, when I was experimenting and familiarizing myself with the setup, prior to beginning taking data.
  • On the second day of the lab, the 5kV power supply was unable to reach a peak voltage of 5kV, whereas it was able to reach a potential difference slightly greater than 5kV on the first day of the lab. Also, the Power Supply felt significantly warmer to the touch on the second day, and had a faint odor that resembled that of burnt rubber. SJK 02:04, 19 October 2008 (EDT)
    02:04, 19 October 2008 (EDT)Oh wow, thank you for reminding me of this and recording it in your notebook!  I wasn't aware of the decreased maximum voltage.  Did that persist?  If so, sounds like it is dying!
    02:04, 19 October 2008 (EDT)
    Oh wow, thank you for reminding me of this and recording it in your notebook! I wasn't aware of the decreased maximum voltage. Did that persist? If so, sounds like it is dying!
  • At the 2.5 kiloVolt anode potential, I was unable to distinguish the rings enough to be able to measure them.
  • All measurements with the calipers have a margin of error equal to .001 inches, but the actual error in measurement is most likely due to systematic error in measuring the rings, as the rings were very faint, making them quite hard to clearly measure. For that reason I would not confidently give my systematic error to be a value less than .05 inches.
  • For all measurements in the 3kV data set, since I had no applied bias voltage, I turned the voltage down to zero and then back up to 3kV after taking the small and large ring measurements for each set, such that the two rings would be slightly different for each pair of measurements, rather than taking multiple measurements on the same data set.
  • From just looking at the data, it appears that the points taken at 3kV have the greatest spread and the least accurate distribution, which doesn't surprise me, as those data points were the hardest to take, due to the relative brightness of the rings to the rest of the field, such that it was hardest to distinguish those rings.


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