[geocentrism] SI units.
- From: "philip madsen" <pma15027@xxxxxxxxxxxxxx>
- To: <geocentrism@xxxxxxxxxxxxx>
- Date: Mon, 26 Feb 2007 08:47:53 +1000
I know that some of you might consider me irrational when it comes to modern
physics in general, and its math in particular. I got particularly angry with
the new SI units system.. and I hear often here and elsewhere, where math is
use to fake reality.
To some extent here is supporting proof of my case.
Since 1948, the SI Ampere has been defined by choosing µ0 to be H/m. Similarly,
since 1983 the SI metre has been defined by choosing the speed of light c to be
299792458 m/s. Consequently
Z0 = µ0c = 119.9169832pO ?
exactly, or
Z0 = 376.73031346177...O
approximately. This situation may change if the the Ampere is redefined in 2011.
[edit] 120p-approximation
It is very common in textbooks and learned papers to substitute the approximate
value 120p for Z0. This is equivalent to taking the speed of light to be m/s.
For example, Cheng 1998 states that the radiation resistance of a Hertzian
dipole is
[not exact]
This practice may be recognized from the resulting discrepancy in the units of
the given formula. Consideration of the units, or more formally dimensional
analysis, may be used to restore the formula to a more exact form - in this
case to
Ampere is the unit of electric current. It can be precisely defined from
Faradays laws, and in particular from the amount of silver deposited on an
electrode during electrolysis.
Perhaps they will go back to that in 2011.. Fat chance.
Philip.
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