Re: Millikan Apparatus- best one ?

[Jon Bell <jtbell@cs1.presby.edu>]

 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