# Physics307L F09:People/Long/Millikan2

## Purpose of the Millikan Oil drop experiment

Using the Millikan oil drop apparatus, one can calculate the elementary charge. This is achieved by recording the velocity of an oil droplet as it falls and rises in an electric field. Using these velocities and the potential of the field, an equation can be used to calculate the charge of the electron. This experiment requires patience, and can be very hard on one's eyes, so Tom and I decided to experiment with a variety of cameras to improve this experiment. Unfortunately we did not yield any success with the cameras

## Data Summary

Our mean charges with uncertainties for each drop are as follows:

Drop 1: ${\displaystyle 1.17(4)\cdot 10^{-19}C}$

Drop 2: ${\displaystyle 2.7(1)\cdot 10^{-19}C}$

Drop 3: ${\displaystyle 1.3(4)\cdot 10^{-19}C}$

Drop 4: ${\displaystyle 2.5(1)\cdot 10^{-19}C}$

Drop 5: ${\displaystyle 1.2(2)\cdot 10^{-19}C}$

Drop 6: ${\displaystyle 1.1(1)\cdot 10^{-19}C}$

Drop 7: ${\displaystyle 2.5(10)\cdot 10^{-19}C}$

Drop 8: ${\displaystyle 2.2(1)\cdot 10^{-19}C}$

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

e = ${\displaystyle 1.602176487(40)\cdot 10^{-19}}$C

Our measurements show that our droplets have on the order of 1 to 2 electron charges, but no definitive integers, to say exactly how many electrons...SJK 18:34, 14 November 2009 (EST)
18:34, 14 November 2009 (EST)
I guess with only these charges, it probably would have been difficult to deduce the value of "e." However, I would have wanted you to try (see John Callow's method, for example). Also, if that didn't pan out, I'd want more discussion of your apparent charge values with the accepted values of "e", "2e", "3e", etc. ... are the integer values of "e" within the error bars of your charges?

See my Lab Notebook for a full outline of procedure or click here for my excel spreadsheet and chart.

## Conclusions

This lab was a good learning experience for me for a number of reasons, we experimented with a number of cameras with the apparatus, which was great as far as problem solving goes, despite not yielding any good results with the cameras. However, with the data we obtained the first week, we were able to analyze it correctly unlike the first time we attempted this experiment. I experienced a great deal of frustration and struggled to understand error propagation, since we were dealing with the two variables of velocity up and down. Tom showed me the link that Dr. Koch emailed to him about propagation of uncertainty using partial derivatives. It took a great deal of explaining (thanks again Tom), but I feel that I have a good grasp of the technique. Finally this was an excellent experience for me as far as excel manipulation, the largest challenge for me in that program is organizing the data in decently convenient ways. I also figured out how to chart my values for each droplet, and also the error bars for my corresponding SEM's.SJK 18:36, 14 November 2009 (EST)
18:36, 14 November 2009 (EST)
I'm glad this was a great learning experience for you. I'm pretty sure we'll go over the error propagation on Monday, and it will probably make a lot of sense to you hfter having gone through this.