# Millikan's experiment.

#### decamij

Using BASIC physics, and being given some results of Millikan's experiment, how would i calculate elementary charge. Basic physics means using the following equation:

q = mgr
V

Here are some results:

mass (kg) voltage (V) distance (m)
3.2X10^-15 140.0 0.005
2.4X10^-15 147.0 0.005
1.9X10^-15 290.9 0.005
4.2X10^-15 214.4 0.005

i used the above equation to find the charge on each oil drop. Then what do i do?
P.S. I'm only in grade 12, and i only the basics of this topic. Please don't use crazy 4th year advanced physics.

Thanx a lot

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#### TeethWhitener

Gold Member
If you calculate the charge on the drop for each experiment, you get:
$1.12\times 10^{-18} C$
$8.0\times 10^{-19} C$
$3.2\times 10^{-19} C$
$9.6\times 10^{-19} C$
Assuming that the elementary charge is an indivisible unit tells you that the charge on an oil drop must be an integer multiple of the elementary charge (so you can have, e.g., 3, 8, or 17 charges on an oil droplet, but you can't have a fraction of a charge). With this knowledge, finding the elementary charge is as straightforward as finding the greatest common divisor of the charges on individual oil drops.

"Millikan's experiment."

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