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*From*: Jon Bell <jtbell@cs1.presby.edu>*Date*: Fri, 11 Oct 1996 23:13:05 +0000

Leigh Palmer <palmer@sfu.ca> 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 <jtbell@presby.edu> Presbyterian College

Dept. of Physics and Computer Science Clinton, South Carolina USA

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