Re: Millikan Apparatus- best one ?

[palmer@sfu.ca (Leigh Palmer)]

> I think I had the same experience as you.  As a student we measured only 5
> drops, but one had very nearly twice the charge of another.  The other
> three had approximately 3/4 the charge of the smaller of the first two, so
> we guessed the last three each had three units of charge apiece, and then
> one had four and the other 8.  Using least squares we calculated
> e=1.675E(-19) C.  Unfortunately we weren't required to calculate the
> uncertainty in this, only the percent error.
>
> Even using so few drops there is little possibility that all of them might
> have an even # of charges and so would yield 2e instead of e.

I had hoped someone else would join the interrogation, but no one did.
Did it occur to you to wonder why Millikan had to measure many more
than five drops? (I think he measured thousands.) 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!

Five drops is certainly not sufficient to measure the quantum of
charge. The whole point of the measurement is missed if students are
instructed to measure five charges.

Leigh