User:Matthew Cordova/Notebook/Physics 307L/2010/10/27

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Steve Koch 22:23, 21 December 2010 (EST):Very good primary lab notebook. Great discussion of the problems and ideas for better work in the future.


  • Multiple current/voltage sources will be in use. Handle with care.
  • Be sure not to exceed 2.5V on Vf. This could damage the equipment.
  • Don't break the bulb.


  • Soar Corporation DC Power Supply Mod. 7403 ([math]V_f[/math])
  • Kepco Regulated DC Supply Mod. CK60-0.5 ([math]V_A[/math])
  • Tel 2501 Universal Stand
  • Hertz Critical Potential Bulb #2533
  • Tel 2021 Alarmed Meter and Stand
  • Tel 2533.06 Battery Unit
  • Wavetek Voltage Meter

Set Up

Full Setup (without digital Voltmeter)

A detailed set up can be found in Prof. Gold's lab manual. The diagram to the left provides everything necessary to do this lab. And while this diagram seems rather straightforward, Sebastian and I had some trouble with it. The meter which measures the current obtained in the ring was complicated, and always provided a value, whether or not the equipment is set up correct or not (this is most likely due to the fact the meter records very small currents). This made it rather difficult to know if we had the correct set up (taking a few data points at different voltages to see if you get coherent data is recommended). Also, while the voltage source has a meter on it, we used a digital voltage meter in order to get a more accurate reading of the voltage.

  • Note: We had some problems keeping all the wires secure. Make sure to double check all wires before taking data.


Nearly the entire first day of lab was dedicated to set up. For the second day, Sebastian and I proceeded to take our data which consisted of recording the current measured in the metal ring (located in the bulb of Neon gas) at different voltages (a higher voltage means greater [math]e^-[/math] energy). For the first trial, we set [math]V_A[/math] to 2.1 volts. With the electric volt-meter attached to the voltage source (for increased accuracy), we measured the current in the ring at 0 volts, and increased this to 30 volts at intervals of 1 volt. With this data, we can observe where we can expect to see the excitation level for Neon, and we can 'zoom in' on this voltage by taking more data points using smaller intervals (in our case .25 volts) to obtain a clearer graph of current vs. voltage near the excitation level. We then flipped the battery in order to measure ions instead of [math]e^-[/math]s. With this, we can observe at which point Neon gas is ionized. The slope of the graph of ions vs. voltage greatly increases at the ionization point. For the second trial, we set [math]V_A[/math] to 1.8 volts and repeated the process.

  • Note: The equipment used in this lab are quite sensitive. Even bumping the table could cause 'bad' data.

Calculations and Results

Excel Sheet


Since we were only able to take a single trial for each voltage, the analysis of our data is going to be pretty straightforward. If we inspect the graphs (found in the excel sheet) of current vs. voltage, we can observe where the peaks of current are measured. For the 2.1V trial, it can be seen that there is a peak at 18V and 21V. With this knowledge, we can assume that Neon has excitation levels at 18eV and 21eV. Since our graphs measure over intervals of .25V, we must assume this to be our range of error. Similarly, for the 1.8V trial we have peaks at 18.25V and 20.75V. Also, since the graph is horizontal at 16.25 and 16.5V, a local maxima is likely present in that range. Two horizontal points are also found at 18.75 and 19.0V. A local maxima is also likely to be present in this range. In conclusion,

  • At 2.1V, Neon is observed to have an excitation level at:
    • 18 +/- 0.25 eV
    • 21 +/- 0.25 eV
  • At 1.8V, Neon is observed to have an excitation level at:
    • 16.375 +/- 0.125 eV
    • 18.25 +/- 0.25 eV
    • 18.875 +/- 0.125 eV
    • 20.75 +/- 0.25 eV

For the ionization level of Neon, we can see that the slope of the graph (for both [math]V_f[/math]= 2.1V and 1.8V) gains a steep increase somewhere around 22V. We can assume from this data that the ionization level for Neon is at around 22eV. It would have been very useful to take more data points around this voltage, but we neglected the importance of this sudden change in current increase while taking our data. In conclusion, with the limited data we have, we can say that:

  • The ionization level for Neon is 22 +/- 1 eV
    • Note: Sebastian and I were clearly unprepared for this lab. Not only did we only take a single trial for each voltage, but we assumed that an interval of .25V would yield accurate enough results to obtain all the excitation levels of Neon. If we were to do this lab again using smaller interval levels and multiple trials per voltage level, a much more useful error analysis would be possible.

The accepted values for the excitation levels of Neon are:

  • 16.7 eV
  • 18.65 eV
  • 19.75 eV
  • 20.1 eV

In Gold's manual, he mentions that all the values should have an expected constant offset. Even with our limited results, this can be seen. Nearly all of our values (excluding the last excitation level) fall below the accepted values. This could be due to the fact that we have very limited data, or it may actually reflect the offset mentioned by Gold. With such a little confidence level in our data, we can not say for certain what we actually have.
The accepted value for the ionization level for Neon is

  • 21.56 eV

We actually came pretty close to this value in both trials. I can say with some confidence that if more data (at smaller intervals) had been taken for the ionization of Neon around 22V, we would have an even more accurate value than our data represents.
In conclusion, the data we have is very limited, but not entirely unusable. Values for the excitation levels as well as the ionization level of Neon were found. Our percent error for the measured values are as follows:

  • [math]\frac{16.7-16.375}{16.7}*100=1.9%[/math] error for our first measured excitation level.
  • [math]\frac{18.65-18.25}{18.65}*100=2.1%[/math] error for our second measured excitation level.
  • [math]\frac{19.75-18.875}{19.75}*100=4.4%[/math] error for our third measured excitation level.
  • [math]\frac{20.75-20.1}{20.1}*100=3.2%[/math] error for our final measured level.
  • [math]\frac{22-21.56}{21.56}*100=2.0%[/math] error for our measured ionization level.

I have chosen to not include the trial for [math]V_f[/math]= 2.1V due to the fact that there were only two measured excitation levels, and averaging them seemed like a good idea at first, but then Sebastian mentioned they did not share the same parent distribution.
Error in our data could be caused by the sensitive nature of the equipment. The pico-amplifier measures very small currents, and every little vibration in the system is observed on the meter. Also, the fact that I only have one true trial that I used for data couldn't possibly be good science.


Thanks to Brian Josey for the picture for the set up. Also, thanks to Tomas A. Mondragon for uploading the image in the first place. Thanks to Alex Benedict for general help with this lab.