Physics307L F08:People/Martinez/Electron Spin Resonance

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  • This lab was intended to study the intrinsic properties of the electron spin flip. The resonance frequency at which the electron will change energy in a magnetic field between the two energy levels. Essentially we conducted our experiment to find a value for the intrinsic g-factor that was the only piece we were not privy to in our equation for the dipole moment of the electron. Our experiment consisted of putting a electron source into a nearly uniform magnetic field provided by Helmholtz coils, then we used an RF oscillator to induce photons into our electrons to make them flip if they were at the necessary energy level, and finally we picked up the energy of the flips by using a search coil which collected the radio frequency of the electrons. This setup was extremely similar to that for a MRI machine. The setup for the systems circuit was incredibly complex and took us the majority of both class periods to troubleshoot problems, and finally we collected a small amount of data about the current and frequency by matching on the oscilloscope two plots, one which provided a steady alternating current and the other the which had sharp spikes where the electrons flipped, we matched the spikes to the graph of the Helmholtz current when the AC had reached zero to avoid any calculations about the voltage. It would be hard to say where our main problem was in this lab, the entire thing was problematic from the circuit construction to the data collection and the data analysis were all wicked hard.
  • wiki page for this LabUser:Stephen K. Martinez/Notebook/Junior Lab/2008/11/12
  • we weren't sure which data we should report, we conducted our analysis in several different ways, I think that we decided to use the data we got from doing the linest model, and the two ways differ based on our values for the quantities within the equation - for example the quotation in the lab manual for the bohr's magneton was in eV/G which we had no idea what G was, so for the first method we pretty much plugged in everything as we thought it was correct:
SJK 23:42, 17 December 2008 (EST)
23:42, 17 December 2008 (EST)
I looked at your Excel sheet and when I put in the values I get something like 1.95 for the g value. So, I think you guys just made a typo or used the formula incorrectly. (G is Guass)

g_s=4.793 ±.003 which is extremely far from the accepted value of 2.0023 and has a percent error of about 139%,

the other method we used followed Linh's analysis whose page can be accessed in the lab notebook, and who we referenced pretty much continuously throughout our lab experiment, he did something and we are not sure of the justification, but his method gave our numbers a brilliant closeness to the accepted. essentially we were having a problem with the magnitude of our axis, it appeared as if Linh removed this problem by eliminating the scaling factors so that for some reason the 10^-6 and 10^-12 were plotted on the same scale, which we almost achieved when we changed our values from eV/G to eV/T although we were still of by a single order of magnitude from Linh.

g_s=2.086±.02 which differs in error by only 4.31%, although the accepted still does not fall within the first standard deviation.

The error from this lab is most likely from our calculations of the magnitude of the constants as stated earlier, There were some problems with the lab set-up for example it was by eye that we matched the peaks with the zero point of the alternating current, but I feel confident that the points we eventually recieved were good, it would have been much better to have more data to work with though.

  • I learned about electrolytic capacitors, and not to mess with them because they suck, the lab was actually really fascinating, I think I almost understand what is going on which I am sure by now is assuredly a novelty, but that knowledge is purely with respect to the theory when we got in there it was all crazy, but if it hadn't been for all the problems with the setup etc. I think this is the coolest lab in the manual, what a cool thing to measure - so advanced in physics and yet it is still very accessible theoretically.
  • Suggestion- maybe have this lab already set up like the diffraction grating: without the setup fears I think a lot of people will be interested in this one.
SJK 18:43, 17 December 2008 (EST)
18:43, 17 December 2008 (EST)
I'm not sure what I think about this suggestion. I mean after all, you survived and ended up liking the lab, and probably learned a lot more through your stuggles (that's my guess). I think it would be a lot less useful if it were a "canned experiment," plus I wouldn't be able to use the alternate name, "life lessons in electrolytic capacitors."