15 Apr
2011
15 Apr
'11
3:55 p.m.
On 2011 Apr 15, at 11:47 AM, Tony Duell wrote:
I expect that what your instructor was getting at was that the use of
an AC bridge typically involves comparison with another C, which also
needs to be measured. It becomes a 'turtles all the way down' problem.
This would be in contrast to a solution which examines Cx in terms of
the definition of capacitance (time/charge) and breaks it down to more
fundamental/axiomatic measurement units (i.e.,time,mass), even though
this does involve comparison to some other standard.
"That is a comparison and not a measurement" may not be a full
expression of the distinction, but I think your instructor had a point.
I'm not up to scratch on my measurement theory, what are the
fundamental standards these days?, there's oscillation of the cesium
atom for T, there was the Meter bar in Paris for D, but hasn't that
been redefined?, etc. Or, how many fundamental standards do we need to
derive everything else? 3?.
On 13/04/11 14:45, Dave McGuire wrote:
> If someone tried to feed me that garbage in a school, I'd demand my
> money back. Bravo for trimming the fat from your stuff.
Actually, that is minor compared to some of the garbage I was 'taught'
at
school. I fact I don;t think I ever had a clueful matehmatics of
physics
teacher.
I think the wordst was when I was aksed to descrtivbe a method of
measuring something (the capacitance of a capacitor). I did so (an AC
bridge) and was told 'That is a compariston and not a measurement', I
am
still waiting for a definition of 'measurement' (or an esample of one)
which
does not involve a comaprison to a standard.