Physics307L F09:People/Ritter/Neon
Excitation Levels of Neon
To view the exact procedure for this lab or to learn more about the apparatus follow the given link to last year's lab manual.
Purpose
This lab is designed to show the work done in the Frank-Hertz experiment of 1914 which was done to prove the quantization of energy in atoms. In this experiment we will fire free electrons to at neon atoms to show that a certain minimum energy is required to break free electrons. This collision that occurs moves bound electrons to an excited state. This experiment should show what these minimum energies are by the observed peaks.
Equipment and Setup
We used a Hertz Critical Potentials tube filled with neon connected to a Picoamplifier with Alarmed Meter, Power Supply and Digital Multimeter as shown in the figures to the right. We setup the apparatus to work with the multimeter and power supply so that we could read the exact voltage going into the apparatus. We then used the alarm to read the amps in the tube this should give the peaks where the excitation levels spike giving us the values for the different electron transitions possible in neon.
Calculations
After two days of taking data and not getting any peaks I came back and used the alarm on the picometer to find the peaks. First I set the alarm tight around the signal so it would go off when a peak is passed while slowly sweeping the voltage being used. I was able to find two peaks with the alarm. I then took small measurements over that interval to find the profile of the peaks. I next took larger measurements around the peaks to show the overall curve coming into and out of the peaks. The peaks fell around 17.66eV and 18.45eV. These represent the [math]\displaystyle{ 2p^53s }[/math] and [math]\displaystyle{ 2p^53p }[/math] transitions. In our data there is also a peak around 20eV that represents the [math]\displaystyle{ ^14s,^23d }[/math] transition which is harder to see as while taking data this feature is less prevalent and therefore I didn't notice it until I was looking at the data while writing it up. If I had noticed it before I could have resolved it better while at the apparatus. The accepted peak values according to the Physics 307 Lab Manual appendix C for the first two peaks are 16.7eV and 18.65eV respectively. This gives us a 6% relative error in the [math]\displaystyle{ 2p^53s }[/math] transition and a 1% relative error in the [math]\displaystyle{ 2p^53p }[/math] transition.
Conclusions
1.) Using the alarm - Using the alarmed meter we were able to find two peaks similar to the ones in the manual. It was very important to keep the alarm close to the signal profile to see the peaks when they came by. I was glad to have the extra time on Wednesday to re-take data. I felt I learned a lot about the procedure and have a deeper understanding of the process involved. This experiment showed the quantization of atoms by showing that there are specific energies necessary to have an electron change states if this wasn't the case we wouldn't have spikes the curve would be constant as any energy would cause a state change. Here we see that there are quantized energies needed to make those transitions. I feel with more time to take readings we could have gotten lower percent error in our eV numbers and we could have easily with more time resolved the [math]\displaystyle{ ^14s,^23d }[/math] transition better and been able to find its peak with a lot more accuracy.
