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Re: Millikan Apparatus- best one ?

Leigh Palmer <> wrote:
If your uncertainty
in measurement of the absolute charge on that 8e drop was +/-5% then
you could not even claim that the number of charges was 8; it could
easily have been 7 or 9!

A recent issue of _American Journal of Physics_ describes some
improvements the author made to a standard Millikan apparatus and
experimental procedure. In order to cut down the uncertainty in the
drop velocity measurements, he requires students to measure each velocity
several times for the same drop, then find an average.

Working backwards from the known value of e, I once calculated the
expected travel times for drops in our apparatus. Even at the highest
electric field we can produce, by the time "n" reaches five or so, the
times for successive values of "n" become close enough together that you
cannot distinguish them reliably with a single measurement.

And very few of our students have the patience to look for the *really*
slow-moving drops.

Jon Bell <> Presbyterian College
Dept. of Physics and Computer Science Clinton, South Carolina USA