Physics307L:People/Meyers/Millikan Oil Drop Lab Summary II

MILLIKAN OIL DROP LAB (again)

Purpose
The purpose of this lab was to determine the value of the fundamental charge. A cursory goal was to understand more about the experiment and physics fundamental charge.

Procedure
The procedure for this lab is posted

Procedure Notes

Three important things that we forgot about on the second day of lab.


 * Clean the equipment fully before each use.


 * Make sure the focus on the microscope is sharp.


 * If there are no droplets after the above two notes are completed, you can remove the cap off the top capacitor plate to aid in production of drops.

Data
Mean fall velocity: $$3.918*10^{-5}m/s$$
 * Particle 3:

Mean rise velocity: $$8.66*10^{-5}m/s$$ Mean fall velocity: $$3.036*10^{-5}m/s$$
 * Particle 4:

Mean rise velocity: $$1.134*10^{-4}m/s$$ Mean fall velocity: $$3.269*10^{-5}m/s$$
 * Particle 5:

Mean rise velocity: $$1.026*10^{-4}m/s$$ Mean fall velocity: $$3.595*10^{-5}m/s$$
 * Particle 7:

Mean rise velocity: $$1.271*10^{-4}m/s$$ Mean fall velocity: $$3.150*10^{-5}m/s$$
 * Particle 8:

Mean rise velocity: $$3.85*10^{-5}m/s$$ Mean fall velocity: $$3.6250*10^{-5}m/s$$
 * Particle Thorium:

Mean rise velocity: $$4.2860*10^{-4}m/s$$

Calculation
Using the rise and fall velocities we can calculate the fundamental charge q

$$q={4/3 \pi \rho g}{\Bigg[}{\sqrt{\bigg({\frac{b}{2p}}\bigg)^2+\frac{9ηv_f}{2g\rho}}-\frac{b}{2p}}{\Bigg]^3}\frac{v_f+v_r}{Ev_f}\,\!$$

I used this equation to calculate the pressure.

Using this equation and a MATLAB program I wrote I calculated $$q\,\!$$ to be:

Particle 3: $$q=1.566*10^{-19}\pm 1.1*10^{-20}C\,\!$$

Particle 4: $$q=1.539*10^{-19}\pm 5.1*10^{-21}C\,\!$$

Particle 5: $$q=1.525*10^{-19}\pm 6.7*10^{-21}C\,\!$$

Particle 7: $$q=1.954*10^{-19}\pm 4.5*10^{-21}C\,\!$$

Particle 8: $$q=1.534*10^{-19}\pm 6.9*10^{-21}C\,\!$$

Thorium Particle: $$q=1.5977*10^{-19}\pm 3.1*10^{-20}C\,\!$$

Averaged together we get a q of:

$$q=1.643*10^{-19}\pm 6.8*10^{-21}C\,\!$$

Error
With the accepted value of q as:

$$q=1.602176487(40)*10^{-19}C\,\!$$

This is inside my first standard deviation of mean of my calculated q.

Also the percent error is:

$$%error=\frac{(1.643*10^{-19}C)-(1.602*10^{-19}C)}{1.602*10^{-19}C}x100%=2.56%\,\!$$

This is very good.

Conclusion
Compared to the first time we did this lab we have done much better. We found a $$q\,\!$$ and a standard deviation that contains the accepted value of $$q\,\!$$. From last time, we changed one fundamental thing, time. We took the time to take more data and make sure that it is good data.

Citation
1)Pressure versus altitude equation here

2)Altitude of Albuquerque here

3)Wiki math help here

4)Accepted value of q

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

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