Re: c = inverse(sqrt(epsilon nought *mu nought))

Wade Ward wrote:
On May 20, 9:32 pm, har...@xxxxxxxxxxxxx (John Harper) wrote:
In article <1179703684.134338.96...@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>,
Wade Ward <zaxf...@xxxxxxxxx> wrote:



With MM posting a value for c at tens of thousands of meters per
second less than 3 x 10**8, this forces either
C =(E0*U0)**(-.5) to be an approximation or
E0=(1E-9)/(36*PIE)
U0=(1E-7)*4*PIE are approximations.
Not quite. You don't say what units you are using, but in SI units
both C and U0 above are both exact, E0 is an approximation.

The SI definitions give the units of U0 as N/A**2 = kg m s**(-2) A**(-2),
C as m/s, E0 as F/m = kg**(-1) m**(-3) s**4 A**2.
(If you invent suitable derived types you can even make Fortran do
your units as well as your numbers)

See, for example,http://www.physicstoday.org/guide/fundcon.html
I'm able for the first time in a while to surf the net and see at the
above link that c is defined as a rational slightly less than 3 x
10**8 and U0 is indeed as above. Wouldn't that force E0 to be
irrational as well?

Why is the irrationality a problem? They're still constants:

c = 299792458 m.s^-1 (exact)
u0 = 4pi x 10^-7 N.A^-2 (exact)
e0 = 1/(u0.c^2) F.m^-1 (exact)

where the "exact" refers to the uncertainty of the value (in a vacuum). Since they are all defined quantities, not measured, their knowledge is considered "exact".

cheers,

paulv

--
Paul van Delst Ride lots.
CIMSS @ NOAA/NCEP/EMC Eddy Merckx
.

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