Date: Sun, 5 Apr 2009 15:52:03 -0400
Reply-To: Mike S <mikes@FLATSURFACE.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Mike S <mikes@FLATSURFACE.COM>
Subject: Re: Learning Electricity Part Two
In-Reply-To: <49d8e943.0936640a.1a38.ffffb731@mx.google.com>
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At 12:23 PM 4/5/2009, David Beierl wrote...
>First, I learned electricity in the '50s. Yes,
>I know I was only eight...<shrug>. The Systeme
>Internationale did not exist prior to 1960 and
>wasn't taught to the trade until long after;
How very hypocritical of you to further a
discussion of SI units for electricity after
asking me not to (in pmail - "please -- let's
leave SI out of it...this stuff is scary enough
as it is..."). But, since you have, metrology is
one of my hobbies, and it irks me when someone gets it wrong.
Technically the Systeme Internationale started in
1960, because that year saw a change in name, but
the basis for international electrical standards existed long before.
The coulomb, going back to its first definition
by the 1st IEC in 1881, has always been a derived
unit. The British Association for the Advancement
of Science at Edinburgh in 1892, defined the
ampere as that unvarying current that would
deposit 0.001 118 000 grams of silver per second
from a solution of silver nitrate in water. The
coulomb was derived from this, being the amount
of charge delivered by 1 ampere in 1 second.
By the 1950's, the ampere was included in the
International System of Electric and Magnetic
Units as a fundamental unit of electricity. In
1950, the ampere was defined by US Law as a
fundamental unit, and the same law shows that the
coulomb is a derivation. (15 USC Sec. 223)
http://uscode.house.gov/uscode-cgi/fastweb.exe?getdoc+uscview+t13t16+988+1++
The 9th CGPM (1948) adopted the ampere for the
unit of electric current, following a definition
proposed by the CIPM (1946, Resolution 2), the
same definition which is used in the SI: "The
ampere is that constant current which, if
maintained in two straight parallel conductors of
infinite length, of negligible circular
cross-section, and placed 1 metre apart in
vacuum, would produce between these conductors a
force equal to 2 x 10–7 newton per metre of
length." - source BIPM,
http://www.bipm.org/utils/common/pdf/si_brochure_8_en.pdf
That definition of the ampere became an official
base unit of the "mks" system, along with the
kelvin and the candela, at the 10th CGPM, in
1954. The "mksA" system then went on to be renamed as the SI in 1960.
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