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

In article <f2sr4o$p8f$1@xxxxxxxxxxxxxxxxxx>,
Paul van Delst <Paul.vanDelst@xxxxxxxx> wrote:
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:

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.

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".

I have another problem with Wade's terminology. c is a velocity, which
happens to be a rational (for that matter an integer) number of metres
per second, which Paul gave. c is NOT a rational number. Rational
numbers are dimensionless. Remember the spacecraft that crashed on Mars
because someone was careless with units...

-- John Harper, School of Mathematics, Statistics and Computer Science,
Victoria University, PO Box 600, Wellington 6140, New Zealand
e-mail john.harper@xxxxxxxxx phone (+64)(4)463 5341 fax (+64)(4)463 5045
.

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