Re: [Phys-L] thermometry

[Prof Keith S Taber <kst24@cam.ac.uk>]

My understanding (and what I used to teach when I was real science 
teacher) is that "the property change of a thermometer which corresponds 
to a temperature change" is linear by definition. So on a mercury 
expansion thermometer the temperature scale is defined linearly by the 
expansion of the mercury - generally temp t = (Pt-Pl)/(Pu=Pl) where P is 
the measured property at the lower (Pl), and upper (Pu) fixed points and 
the temperature being measured/interpolated (Pt). This is why 
thermometers can only be assumed to agree at the fixed points (and any 
temp measure should state the scale, i.e. type of instrument, used).

Is that still the convention?

Keith


> There's nothing that says that the property change of a thermometer which corresponds to a temperature change must be linear. All that is required is that the change can be calibrated and reproducible and a function of temperature. Monotonic would help, but I suppose one could keep track of small changes with constant monitoring devices to make sure that the reported temperature isn't discontinuous compared to previous values. One could also account for hysteresis effects if you're clever.
>
> -----Original Message-----
> From: Phys-l [mailto:phys-l-bounces@mail.phys-l.org] On Behalf Of bernard cleyet
> Sent: Friday, February 2, 2018 12:38 PM
> To: phys-l@phys-l.org
> Subject: [Phys-L] thermometry
>
> The current discussion on internal energy has me puzzled about the accuracy of measuring temperature depending on expansion.  Is not expansion non-linear?  Are expansion methods comparable to non-expansion methods (speed of sound- E-M radiation, etc.) comparable, because the the expansion is small, so a linear “first term” is “OK”???
>
>
> bc
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