User:Jared A. Booth/Notebook/Physics 307L/2009/09/21

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Milikan Oil Drop


The purpose of this lab is to attempt to measure the electric charge of an electron in the same manner as Milikan.


PASCO scientific model AP-8210 Milikan Oil Drop Apparatus
High Voltage power source
LG Voyager phone (as stopwatch)
4 banana plug patch cords


A high voltage power source (~500V DC) will be used, so it is essential to check all equipment for damage.


The procedure was followed according to the manual included with the PASCO Apparatus.

Raw Data

Width of plastic spacer: Using a calibrated micrometer, d=5.60mm with uncertainty +/- 0.01mm Voltage applied to apparatus: 499.0V DC Thermistor Resistance: 2.070 kohm Temperature from Table: 24.55°C

All fall and rise times were calculated as the droplet covered a distance of .5mm
Droplet 1

Rise time in seconds: 8.59
Fall time in seconds: 12.57, 10.33, 10.75

Droplet 2

Rise time in seconds: 16.83, 18.62
Fall time in seconds: 13.83, 12.34, 14.46, 14.8
The droplet spontaneously reversed charge after a few measurments.

Droplet 3

Rise time in seconds: 5.74, 2.79, 2.58, 2.72
Fall time in seconds: 25.42, 30.24, 29.54

Droplet 4

Rise time in seconds: 5.03, 3.14, 3.00, 3.14, 3.00
Fall time in seconds: 16.69, 13.69, 15.29, 15.36, 14.04

The Droplet spontaneously reversed charge and new measurements were taken.
New rise time: 15.64, 15.5, 15.15, 13.55, 14.81
New fall time: 15.08, 14.46, 13.34, 14.11, 15.64

Droplet 5

Rise time in seconds: 4.47, 4.33, 4.40, 4.33, 4.40
Fall time in seconds: 15.92, 12.58, 14.67, 13.97, 15.55

Droplet 6

Rise time in seconds: 7.75, 7.13, 8.10, 8.31, 8.31
Fall time in seconds: 23.19, 20.19, 24.14, 21.17

The droplet was exposed to a radioactive source for 5 seconds and new measurements were taken. The charge on the droplet was reversed.
Rise time: 7.96, 8.45, 7.90, 8.80, 7.89
Fall time:
The fall time datum were lost due to an error in transfer from timing device.

The droplet was exposed to the radioactive source again.
Rise time: 2.09, 2.10, 2.16, 2.03, 2.16
Fall time: 19.21, 22.36, 20.89, 19.87, 25.78

Since the fall time is independent of charge, and the addition or subtraction of several electrons will have a negligible effect on the mass, it is likely safe to assume the average fall time of the droplet is the same both before and after ionization. Therefore, it would be appropriate to take the average over all measured fall times for droplet 6.

Calculating the charge on the droplets

Using the equation derived in the introduction of the manual for the PASCO apparatus and the rise and fall times measured, we can now calculate the charge on each droplet.


Erica Colon for assistance in recording data.