User:Richard T. Meyers/Notebook/Phys307l/Millikan Oil Drop Lab

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Lab Notes 09/13/10

The procedure on line is here

The Apparatus Setup
The Apparatus Setup
Other Equipment
Other Equipment
Voltage Supply
Voltage Supply


Millikan Oil Drop Apparatus - AP 8210

TEL- Atomic 50V & 500V Supply - UNM 195232

SMIEC Micrometer 0- 25mm

Roberts mineral oil - NDC 54092-417-06 (ρ=886 kg/m^3)


plate separation=7.59-7.60mm

view through the scope a vertical yellow band of light

First Measure

  • Voltage reading (day 1)(i) - 499.9V
  • Voltage reading (day 1)(ii) - 501.3 V (adjusted to 500V)
  • Voltage Reading (day 2)(i) - 499.9 V
  • Voltage Reading (day 2)(ii) - 499.7 V
  • Resistance (day 1)(i) - 2.186 \cdot 10^{6} Ohms
  • Resistance (day 1)(ii) - 2.177 \cdot 10^{6} Ohms
  • Resistance (day 2)(i) - 2.233 \cdot 10^{6} Ohms
  • Resistance (day 2)(ii) - 1.990 \cdot 10^{6} Ohms
  • Temperature (day 1)(i) - 22 centigrade
  • Temperature (day 1)(ii) - 22 centigrade
  • Temperature (day 2)(i) - 20-21 centigrade
  • Temperature (day 2)(ii) - 25-26 centigrade
  • Viscosity (day 2)(i) - 1.826 \cdot 10^{-5} Nsm^-2
  • Viscosity (day 2)(ii) - 1.844 \cdot 10^{-5} NsM^-2
  • Height of Albuquerque approx 1619.1m
  • Pressure p=101325*(1-2.25577*10^(-5)*(h))^(5.25588)=8.333*10^4 Pa
View/Edit Spreadsheet



  • Drop 1: 3.613 \cdot 10^{-17} C
  • Drop 2: 5.851 \cdot 10^{-17} C
  • Thorium Drop: 4.528 \cdot 10^{-17} C

Setting Up Our Equipment

We set up the equipment the same way that the lab manual suggested, cited above. Instead of using the table we decided to elevate the system using the box that the apparatus came in and a thick text book.

Aligning The Optical System

As the lab manual states we used the focusing wire to initially focus the microscope; it suggested that we focus the lens until the right side of the wire reflected the most light and was sharp. The manual then told use to focus the grid lines to clarity using the reticle focus.

Adjusting and Measuring the Voltage

We then adjusted the voltage through the capacitor to about 500 volts, measuring with a multimeter.

Determining the Temperature

To find the temperature in the capacitor space we measured the resistance of the circuit then looked up the corresponding temperature on the apparatus. We also verified this measure with the, less accurate, wall mounted thermometer, in the clock.

The Experiment

We used the first day to set up the experiment, clean the equipment and try to see drops. We were successful in all three of these objectives. We also familiarized ourselves with the lab and became confident in our ability to duplicate the results. Our confidence turned into hubris.

On the second day we spent much of the day trying in vain to see drops. When we asked Professor Koch about our difficulties he informed us of several problems. The first of these problems was a poor focus on the microscope, which we fixed. the next was a dirty plate separator, which we cleaned. The last was the reason for use not having droplets in the space. To remedy this we removed the cap off the top of the top capacitor plate. I believe that this is responsible for both use getting many droplets in the cavity and much of the error in the experiment.

Once these problems were solved we took data sets for two different droplets and then excited one drop with the Thorium.

Using the Thorium

From what I understand the use of Thorium had little effect on our drops. The data shows that the fall and rise time were not affected.


1)Pressure versus altitude equation | here

2)Altitude of Albuquerque | here


1) Nathan for lab help along with data input and help with google docs.

2)Steve Koch for help in trouble shooting the lab.

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