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Re: electric charge



On Friday, December 21, 2001 6:25 AM, Joe Heafner" wrote:

Another hopefully simple question. Is electric charge a
fundamental dimension or is it not? I've seen some texts
treat it as a dimension and some that do not. Which is it?

Paolo Cavallo wrote:

In the International System (SI), electric current is a
fundamental dimension. Charge is current times time.

True enough.

But then you have to decide whether there's anything
"fundamental" about SI. IMHO there isn't. SI was
chosen, and it could have been chosen differently.
http://physics.nist.gov/cuu/Units/history.html

In fact, the people who brought you the meter and
kilogram originally wanted a different definition
of the unit of time:
http://www.physics.rutgers.edu/~ransome/203/Physics203-L1.htm

=========================

In atomic physics, the charge on the electron is
taken as the unit of charge. Can you imagine how
inconvenient it would be to specify the charge on
a calcium ion in terms of the SI unit, the amp-
second? Normaly we say Ca is +2. One could
argue that this is more "fundamental", but since
I'm not a fundamentalist I'd rather just say it
was more convenient and leave it at that.

For macroscopic electrical technology and
metrology, the ampere is more convenient and
more conventional. To call it "fundamental"
would be a bit of a stretch.

By the same token, there is no law of physics
that recognizes the meter or the second as being
fundamental. They are in fact defined as arbitrary
(blatantly non-fundamental) fudge factors times a
certain natural atomic length-scale and time-scale.