i cannot figure out how to do parts 1,2,3 for droplets #1,#2,#3 For each droplet

Question

i cannot figure out how to do parts 1,2,3
for droplets #1,#2,#3

For each droplet that has a different voltage and 5 separate drop times.

I need to calculate:

1-The Radius of the oil drop

2- The weight of the drop

3-the bouyant force acting on the drop

4- the viscous force acting on the oil drop

5- The electric field strength produced when a voltage of "X" volt is applied to a parallel plate separated by 2mm.

PART E: ANALYSIS OF MILLIKAN'S EXPERIMENT (Repeat calculations in part E for droplets #13) The Experiment: Part 1: A charged oil is stationary in an electric field. The electric field is produced by a paralle plate configuration for which the potential difference is and the plate separation is 2 mm. Part 2: The electric field is turned off and the terminal velocity, vt, of the charged oil droplet is measured over a distance of 1 mm by timing the fall Part 3: The electric field is turned on again, the droplet is "caught, and is re-measured. Repeat for 5 measurements. Results Droplet #1: 18.3 V, drop falls 1 mm in times 39.30s, 39.31s, 39.39 s, 39.30s, 39.30s Droplet #2: -29.5 V, drop falls 1 mm in times 59.45s, 59.43s, 59.45 s, 59.46s, 59.45s Droplet #3: =15.2 V, drop falls 1 mm in times 31.63s, 31.63s, 31.61 s, 31.64s, 31.63s

Explanation / Answer

let the radius of the droplet be r
rhooil = 824 kg/m^3
rhoair = 1.293 kg/m^3
n = 1.81*10^-5 kg /m s

now for a potential differnece V
mass of droplet = m
3m/4*pi*r^3 = rhooil
so, for stationary droplet
mg = 1000V*q/2
where q is charge on drop

now, from stokes law
termial velocity vt
vt = 2(rhooil - rhoair)gr^2/9*n

for time T
vt = 1/1000T
hence
1/1000T = 2(rhooil - rhoair)gr^2/9*n

r^2 = 9n/2000T(rhooil - rhoair)g

for drop 1, Tav = 39.32 s
hecne
r1 = 0.5066*10^-6 m
weight, m1 = 4*pi*rhooil*r1^3/3 = 4.487*10^-16 kg

similiarly
r2 = 0.412*10^-6 m
m2 = 2.413*10^-16 kg

r3 = 0.564*10^-6 m
m3 = 6.19*10^-16 kg

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