[Phys-L] Re: Millikan Expt. (was Lab reports)

["David T. Marx" <marx@PHY.ILSTU.EDU>]

Well, I've been doing this experiment with juniors and seniors for four semesters.  The
mean value and the mode value for e is 1.59 x 10^-19 C for the students that have done
the procedures and calculations correctly.  I have the students get as much as they can
from 8 to 10 drops.  This means several transits and exposing a few of the drops to the
active source.

When students do not get close to the accepted value, they blame it on "human error"
associated with starting and stopping the stop watch.  To avoid this, I have them go
though all the motions of the data collection without actually writing it down for the first
hour.  Each member of the group (of 3 or 4) is asked to go through the practice.  Then,
the group decides which person is most comfortable observing and manipulating the
drops.  It turns out that the error is usually in either calculation or the unit conversions.
The unit conversion will often lead to them being off by several orders of magnitude.

The percent error I was referring to is the comparison with the accepted value.  They
are also asked to determine the uncertainty from their data.

One final point, many of the students that get a value of 1.59 x 10^-19 C still use the
"human error" explanation.  Obviously, there is no error that is too small to blame on
human error.

Take care,
David Marx


On 6 May 2005 at 22:55, Hugh Haskell wrote:

> At 17:40 -0500 5/6/05, David T. Marx wrote:
>
> > The majority of students do this experiment quite well and the percent error
> > is generally very small.
>
> Percentage error . . . Didn't we just have a discussion of this? Are
> you talking about the size of the students' error bars, or the
> deviation from the "accepted value." I always ask my students, if the
> "percentage error" is the difference between their result and the
> "accepted" value, how did Millikan calculate his percentage error?
> I've actually had a few answer me, "The same way we do."
>
> Those are the days I head straight for the bar after work.
>
> Hugh
> --
>
> Hugh Haskell
> <mailto:haskell@ncssm.edu>
> <mailto:hhaskell@mindspring.com>
>
> (919) 467-7610
>
> Never ask someone what computer they use. If they use a Mac, they
> will tell you. If not, why embarrass them?
>                         --Douglas Adams
> ******************************************************
_______________________________________________
Phys-L mailing list
Phys-L@electron.physics.buffalo.edu
https://www.physics.buffalo.edu/mailman/listinfo/phys-l