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Re: [Phys-l] calibration



On Aug 7, 2007, at 3:20 AM, Folkerts, Timothy J wrote:

In creating the calibration curve, it makes more sense to me to plot p
horizontally and r vertically. One prepares six samples of an alloy,
each with a fixed value of p. The resistivity of a sample depends on
the percentage p of zinc in the sample.


Quite true, but the apparent goal of the project is to be able to determine the composition
based on the resistivity. Much the way you might determine thickness of a film by measuring the optical trnasmission, or the concentration of a solvent by measuring the density.

although the original samples may have been made with specific compositions, the operation of the meter will take a known resistivity and predict the composition. Hence resistivity really is the independent variable, and composition is the dependent variable.

1) I think that both Jeff and Tim are correct. In the first process (calibration) p is the independent variable. In the second process (inference) r becomes the independent variable; we measure r and we infer p.

2) The asymptotic behavior of the square root formula used in

http://csam.montclair.edu/~kowalski/cf/331calib.html

is intuitively acceptable, as explained in the just-added caption of Figure 2.

_______________________________________________________
Ludwik Kowalski, a retired physicist
5 Horizon Road, apt. 2702, Fort Lee, NJ, 07024, USA
Also an amateur journalist at http://csam.montclair.edu/~kowalski/cf/