Millikan's oil drop experiment simulation
This experiment is a little simplified
We’ve simplified the experiment a little from the one Millikan actually performed. But it should give you some of the flavour of how meticulous Millikan (and/or his assistant Harvey Fletcher) had to be.
Each drop must have a whole number of electrons
Remember the general technique. Find lots of charges due to unknown numbers of electrons then find the common factor.
Simulation Millikan's oil drop experiment to find the charge on an electron. Change the charge on the drops with a radiation source. Time the drops as they rise and fall, then use a cunning graphical tool to find the smallest charge that fits the data.GCSE Maths exam soon?
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It's all about timing drops on the way up and on the way down
The equation the simulation uses to calculate the charge on the oil drop depends on the rising and falling velocities of the oil drop.
So we’ll be timing oil drops and the simulation will calculate the velocities for us. The simulation keeps the mass of all the oil drops the same for simplicity.
You may remember that we (or at least the simulation will) find the mass of the drop from the speed it falls through the air.
You only need to time the drop falling once
When the drop's falling there's no electric field so the number of electrons on it doesn't matter. When it's rising because of the electric field, the more electrons means the quicker it rises.
So we change the number of electrons on the drop lots of times and time it rising on each occasion.
Finding the charge on the electron
The results for charge come in some random order.
There's a cunning little tool to help find how many electrons each charge is caused by. If you know the charge and the number of electrons then you can easily work out the charge on a single electron, which is what the experiment is all about.