User:Ryan P. Long/Notebook/Physics 307L/2009/10/26

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Lab Summary

Note: My partner Tom and I share the same lab notebook up to the Analysis section

SJK 16:33, 14 November 2009 (EST)
16:33, 14 November 2009 (EST)
Excellent primary lab notebook, as usual!


Pictures from the Original Experiment

Pictures from the Continuation

Equipment used in both the original experiment and the followup

  • Pasco Scientific AP-8210 Millikan Oil Drop Apparatus
  • Mineral Oil
  • SMIEC Micrometer
  • Wavetek 85XT Multimeter
  • TEL-Atomic 500V DC Power Supply

New equipment

  • Light similar to the Magnoclip LED Work Light & Laser Pointer
  • Creative USB webcam
  • Logitech USB webcam
  • CCD camera (typical for use in an optics lab)
  • 2" plano convex lens with focal length ~10cm
  • Canon XH-A1 HDV Camera + tripod

Note: We forgot to write down the model numbers of the Logitech, Creative, and CCD cameras, but we will get this information the next time we are in the lab

Week 1- No Camera


First, we tried using the Creative and Logitech webcams to see the droplets and take data. Then we ended up just following the procedure we used in the original experiment.


First, we set up the Logitech camera. The focusing wire was easily seen, but the gridlines were hard to make out due to the camera's low resolution. We tried the same thing with the Creative camera, but again, the gridlines were hard to distinguish from one another. After putting the drops in for both cameras, the light was not bright enough to see anything, despite changing cameras' integration times, contrast, and brightness settings.

After our attempts with the cameras yielded no data, we took data in a similar fashion as the original experiment: we squirted some mineral oil into the chamber with the ionization source set to the spray droplet position. We then turned it off, played with the capacitor plates until we found a suitable drop, and proceeded to time it as it rose with the force of the electric field and fell due to gravity. We did not repeat our previous mistake of measuring the fall time of the droplet WITH the electric field on.

Raw data sheet: {{#widget:Google Spreadsheet

key=tdqXMh97xXnU0W-obvdhVEA width=650 height=300

}} I decided to name our droplets for added excitement


Although the cameras did not work as well as we had hoped, it was still rather interesting to set up each camera and experiment with each. Perhaps they did not work properly because of the optics on the Millikan apparatus, since they are in fact designed to be used with the eye instead of a camera. Another problem could've been with resolution of the cameras we used, the web cams seemed to be too low of resolution to resolve the tiny droplets.

As in the first experiment, I calculated my value of Atmospheric pressure, using Google earth to find the elevation near campus (5187 ft.), and then calculated the pressure with an excellent converter that can be found here.

My value below for q is calculated using the equations on pages 2 and 9 of the pasco manual. Equation for q from page 10:


According to our calculations with our recorded data, our mean charges for each drop are as follows:

Drop 1: [math]1.17(4)\cdot 10^{-19} C[/math]

Drop 2: [math]2.7(1)\cdot 10^{-19} C[/math]

Drop 3: [math]1.3(4)\cdot 10^{-19} C[/math]

Drop 4: [math]2.5(1)\cdot 10^{-19} C[/math]

Drop 5: [math]1.2(2)\cdot 10^{-19} C[/math]

Drop 6: [math]1.1(1)\cdot 10^{-19} C[/math]

Drop 7: [math]2.5(10)\cdot 10^{-19} C[/math]

Drop 8: [math]2.2(1)\cdot 10^{-19} C[/math]

My chart with error bars
The uncertainties were calculated using this wikipedia article, my partials are only approximations based on small changes in velocity, which I would've never figured out without Tom's help, (thanks!). My full spreadsheet and chart can be downloaded here.SJK 16:20, 14 November 2009 (EST)
16:20, 14 November 2009 (EST)
Impressive excel sheet, in that it appears you've shown all the calculations in much detail. However, I have to say I had a tough time following yours and Tom's spreadsheets, since it wasn't exactly the way I would have approached it. So, I can't confirm whether your analyses are correct. Given the amount of care you took in acquiring the data, I'd be surprised if the reason you're off is because of errors in timing. My guess would be either analysis error or perhaps with your new lighting technique, you were not looking in the correct plane, and maybe there was a magnification error.
Although these values aren't very close to the accepted value, and some of the error (especially with number 6 "Pubert") I am pleased with these results as compared to our round one attempt. Next time we'll probably have to take more measurements, and that would hopefully improve our technique and reduce systematic error.

The accepted value of the charge of a single electron is (from wikipedia):

e = [math]1.602176487(40) \cdot 10^{-19}[/math]C

(Steve Koch 16:32, 14 November 2009 (EST):Is Pubert related to Q*bert?)

Week 2- Camera


The second week, we experimented with different cameras to hopefully record some data without straining our eyes! First we tried to set up my canon video camera to monitor the droplets. It could decently see the grid and faintly see the dots, but they were far too out of focus to be recorded accurately. For our second attempt, we set up a CCD camera in front of the apparatus using a 2" lens in between. Also to improve lighting, we removed the built in light source and positioned a stronger LED light in its place.


Since neither cameras weren't entirely successful at viewing the droplets, we weren't able to record any data, and just used the data from week one. The camera's were a constant battle between lighting and focusing, when we could actually see the droplets with the canon video camera, they were out of focus, and the other cameras just weren't sensitive enough to resolve the droplets. Another problem was that this entire apparatus (particularly the optics portion) is designed for the human eye, and not a camera sensor. With a sensitive enough camera, and different lenses, one might be able to pull this off.SJK 16:30, 14 November 2009 (EST)
16:30, 14 November 2009 (EST)
I am confident with enough time and the right optics, you could make it work very well with video. Hopefully even though it didn't work out, you got a good experience trying things out. Here is a paper from Dinesh Loomba (professor in our department) from work he did with Martin Perl's group at Stanford: They had a wicked video tracking setup and were able to track over 42 million drops!