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

[James McLean <mclean@GENESEO.EDU>]

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 like to define "uncertainty" as the size of the students' error bars,
and to define "error" as "the difference between two results, usually in
situations where the uncertainty on one result is much smaller than the
uncertainty on the other."  Making such a comparison seems entirely
reasonable (such as in David's situation of evaluating some equipment),
and the difference so calculated rather closely matches concept
described colloquially as "error."

One then only runs afoul of language when some text wants to speak of
"standard error," which is of course really an uncertainty.

> 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."
I suppose the correct answer would be, "Why would Millikan want to
calculate a percentage error?  He was in a completely different situation."

--
Dr. James McLean                     phone: (585) 245-5897
Dept. of Physics and Astronomy       FAX:   (585) 245-5288
SUNY Geneseo                         email: mclean@geneseo.edu
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