Physics307L F09:People/Mahony/Millikan2

Millikan Oil Drop Lab Revisited Summary

In this lab, my partner Ryan and I followed up on our original Millikan Oil Drop experiment. The procedure we followed is outlined in the Pasco Manual. In addition to taking new data, we investigated the possibilities of using a camera with the Pasco setup, as well as a different light source.

Results

We measured the charge for 8 droplets:

• Drop 1: [math]\displaystyle{ 1.17(4)\cdot 10^{-19} C }[/math]
• Drop 2: [math]\displaystyle{ 2.7(1)\cdot 10^{-19} C }[/math]
• Drop 3: [math]\displaystyle{ 1.2(3)\cdot 10^{-19} C }[/math]
• Drop 4: [math]\displaystyle{ 3.0(1)\cdot 10^{-19} C }[/math]
• Drop 5: [math]\displaystyle{ 1.3(2)\cdot 10^{-19} C }[/math]
• Drop 6: [math]\displaystyle{ 1(5)\cdot 10^{-19} C }[/math]
• Drop 7: [math]\displaystyle{ 2.5(1)\cdot 10^{-19} C }[/math]
• Drop 8: [math]\displaystyle{ 2.2(5)\cdot 10^{-19} C }[/math]

These charges can be compared^{SJK 18:28, 14 November 2009 (EST)}

18:28, 14 November 2009 (EST)
While I'm very happy that you got much better data and made a lot of effort on the camera, I'd want more than "can be compared". What happens if you try to deduce a value of "e" from your data alone? What prevents you from doing that? Knowing what the accepted value of "e" is, are your values consistent, or is there systematic error? etc.

OK, I now see more discussion below, but still much of what I said above is valid.

to integer multiples of the elementary charge of a single electron (from wikipedia):

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

See the Analysis section of the notebook for the calculation of the charges of each droplet.

Despite our extensive testing of the cameras, we weren't able to get any of them in a state where we thought we could take data with them. However, the LED light we used instead of the incandescent bulb in the lamp housing reduced eye strain and made it easier to see the droplets.

Conclusions

Our droplets had charges on the same order of magnitude of 1 to 2 electrons, but were not close enough to any integer value for me to confidently state how many electrons they must have had. The systematic error was simply too large. We must have made mistakes in our timing of the droplets, and might be able to get better results if we took a lot more data.^{SJK 18:37, 14 November 2009 (EST)}

18:37, 14 November 2009 (EST)
Given your familiarity with the apparatus and your practice, I'm doubtful it was timing errors. Perhaps looking in the wrong focal plane?

I also concluded that the use of a camera, at least to the extent that we tested them, does not work well with this lab. However, I highly recommend the use of a bright LED light source instead of the one supplied with the Pasco apparatus.

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