User:Daniel T Young/Notebook/Junior Lab 307L/2008/11/12

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Setup

 * First we removed the apparatus and the pieces from the box and set them on books in order to elevate the eyepiece to a place that would be comfortable for us to through throughout the experiment.
 * Using the individual legs and the bubble level we adjusted the apparatus so it was completely level.
 * We then disassembled the observation chamber so that we could measure the plate separation by measuring the plastic separation width. Plastic separator distance.=7.64mm
 * Then we put the focusing wire into the center and put our light in.
 * Now we need a powerful potential difference that will make a noticeable effect on our charged droplets. We run a power source to our plates making sure to never exceed 500.0 V DC.
 * Then using the focusing wire we focused the eyepiece and calibrated the halogen light.
 * Now we may remove the focusing wire and we are now ready to begin our experiment.

Equipment


 * Voltage Source: 150V - 500V TEL-Atomic Supply


 * Multimeter: True RMS WaveTek Meterman


 * Millikan Oil Drop Apparatus: Pasco Scientific AP-8210


 * Stopwatch: Digital Stop Watch (Radio Shack)

Controls
We have a plate charging switch which can... Also there is a Ionization source lever which has the functions ...
 * give the top plate a negative charge
 * give the top plate a positive charge
 * ground both plates.
 * off which blocks alpha particles from reaching the drop chamber
 * on which allows alpha particles to pass
 * Spray Droplet position which allows air to pass through the chamber.

Plate Voltage=499.5±.1V Thermal Resistance = 2.025±.001 MΩ

Add the Oil

 * We added the oil to the apparatus and now the light reflects off the oil so that we can see them in the eyepiece as the slowly fall due to gravity.
 * By creating a potential difference we can move the charged oil drops up and down.
 * Now we are going to take measurements with a stop watch to measure the time it takes the oil to travel in various Scenarios including...
 * Gravity only
 * Top plate positive Potential difference and Gravity
 * Top plate negative Potential difference and Gravity.

Drop Velocity

 * All rise and fall times were taken of the distance between major reticle lines which is .5mm

No potential Difference

Analysis
Using the data we took over the course of this experiment we should now be able to calculate the charge on the drops we observed, ideally we should be able to show that the charge is some integral multiple of some smallest charge, if we can show this it will be a good indication that electricity is atomic in nature. We might be able to do this with the data we collected, but because we did not change the charge on any of the drops we were observing we will not be able to actually prove that electricity is atomic in nature.

Calculating the charge on a drop involves multiple parts:


 * for each drop we will need to calculate its radius (a) (use eqn # 7, page 2 in manual)

for this calculation we will need...


 * the average fall time, vf, (cm/s)


 * n, the viscosity of air (dyne s/cm^2) (our value (day1) for resistance was2.025MΩ which corresponds to 24.5°C which gives aprox 1.8450*10^ -5 Ns/m^2 which will need to be converted, one N = 10^5 dyne)


 * the constant b = 6.17*10^-4 cm Hg

p = 77.343cm Hg
 * (found pressure for Albuquerque on Nov 19, using the weather underground) 30.45 in or 1031.0hPa (will need to be converted)


 * solve for q, (use eqn # 10, page 2)

this equation has three separate terms;

the fist term only need to be calculated once, it uses


 * d (separation of plates in the condenser in cm) 7.64 mm


 * g (gravity in cm/s^2)


 * ρ density of oil = 886kg/m^3, convert to g/cm^3 (manual gives density of Squibb mineral oil and our brand is the brand that used to be Squibb)


 * n (viscosity of air)

the second termmust be calculated for each drop, it uses


 * a the radius of the drop


 * b pressure constant


 * p the pressure = 77.343 cm Hg

the third term must also be calculated for each trial, it uses


 * average vf in cm/s


 * average vr in cm/s


 * V (potential difference across the plates) 499.5V (I think on day 2 our voltage was slightly lower, if I find that data I will substitute it in here)

e = 4.803 * 10^ -10 e.s.u.
 * Eqn 10 (page 2) will give use the charge q on our drops in e.s.u. (electrostatic units), the accepted value (in e.s.u.) for e is


 * for the pressure conversions I used this link [| pressure conversions]

Note

I retrieved my folder out of lab the Wednesday that this was due and on the day we took the data presented here...


 * Voltage was 483.1 V


 * Temp was 1.843 MΩ ≈ 29.5°C ≈ 1.8680 E-5 Ns/m^2 (viscosity)

I will add a picture of my correct data to my summary, but the change in Voltage and viscosity will have no effect on the final outcome, since I still can not do qualitative data analysis given the deficiencies in our data collection.

Arianna's data analysis

I used both Excel and MatLab to manipulate my data for this lab. Excel for finding the average values and the SEM of my velocities, and MatLab for crunching the lengthy equations and plotting my values of the charge on the oil drops. Both files are attached below.


 * [[Media:Milikan Data.xlsx]]


 * [[Media:Millikan.doc]]