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uncertainties of constants



At 09:12 AM 6/19/97 -0700, Roger Haar wrote:

Hi,

Most of the time I deal with labs, so uncertainties are a big
part of my mind set. Last night it occurred to me that I could not
remember see uncertainties on fundametal constants in most introductory
physics textbooks. This morning, I check, Haliday and Resnick(3rd) had
no uncertainties inside the cover ( and no disclaimer) but did have
uncertainities hidden in the appendix on the constants. Of the 4-5 other
books on my shelf, none seemed presented these constants as anything
other than absolute.

I worry that this is sending mixed messages to the students, in
that in the lab we tell them that all measurements have uncertainities.
I have found students in our junior/senior labs still thinking that
the fundamental constants can be measured perfectly.


Some, of course, are _defined_ or at least agreed-upon by convention. The
speed of light and the permeability of free space (mu-zero) come immediately
to mind. And, since the permittivity (epsilon-zero) is intimately related
to c and mu-zero, it is also defined. Any uncertainty in these quantities
would not be instrumental, but simply a lack of numerical precision.

George Spagna **********************************************
Department of Physics * *
Randolph-Macon College * "A clash of doctrines *
P.O. Box 5005 * is not a disaster, *
Ashland, VA 23005-5505 * it is an opportunity." *
* *
phone: (804) 752-7344 * - Alfred North Whitehead *
FAX: (804) 752-4724 * (Science and the Modern World) *
e-mail: gspagna@rmc.edu **********************************************
URL: www.rmc.edu/~gspagna/gspagna.html