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Millikan Oil Drop Experiment

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Steven J. Koch 01:46, 13 September 2007 (EDT):Great work today getting the experiment to work! Do you have more notes on paper that you haven't entered into the wiki? Some more details are necessary, and it would be great to have a good description of what you think the "tricks" are. Also, for the numbers you do have recorded here, it will be difficult for you to do good error analysis. E.g., 300 V +/- ?. Also 25-26 (25.6) is a good indication of temperature and the range, but it's not clear if 25.6 is some kind of average or what. Probably the temperature drifts, so an estimation of that would be good too.


  • We undid the previous setup (unplugged all of the cables) and started from scratch. We started by identifying that the power source-->experiment-->multimeter circuit was in parallel.
  • Next, we plugged everything back in, leveled the apparatus, and took apart the oil drop viewing chamber.
  • We measured the thickness (using the micrometer)of the plastic spacer to be .759 cm.
  • Focus
    • We reassembled the viewing chamber with the focusing pin in place.
    • Plugged in light source to 12 V DC.
    • Focused viewing reticle onto focusing pin.
    • Adjusted the position of the light bulb to make the focusing pin the most visible. Verified this was so with Dr. Koch
  • We hooked the multimeter up the the plate volatge outlets and measured the voltage. This was to ensure the multimeter and the power source where giving the same readings. We played with and adjusted voltage just to make sure that we were being consistant. We chose an arbitrary value (between 299.6 and 300.4 volts), and left it at that.
    • Note: The voltage was steadily, slowly increasing throughout our experiment! I've given the range based on hand-written records.
  • Temperature
    • Temperature was analysed using a thermistor setup and a corresponding table [1] (pg 11). The tempertaure, like the voltage, steadily climbed as we worked, so we tried to make repeated notice of it. We had a range of 25-26 Celsius, but our data was taken at ~25.4-25.6 Celsius.


Once we had all inital setup in place and double checked, we were almost ready to start. We set the ionization source switch to the Spray Doplet Position , and refilled and fired the atomizer. This consisted of placing the atomizer (filled with mineral oil) above the hole in the viewing chamber and squeezing the blub. One quick squeeze produced an inital mist, and a second, slower squeeze drove out the air. The atomizer had to be pulled away while it was still in astate of expelling air, rather than sucking it back in. One person watched as the other worked the atomizer. The comunication between the two allowed for a great denisty of oil to be seen. We played with the voltage and the ionization source for a while before actually taking data. I think this was important because it helped Brad and I get a feel as to what were were doing and how were should best go about doing it.

  • data will follow