Pi comes up in a lot of places. (I almost said areas...)
Well, if 120 had a different value that wasn't 120, then would the impedance of free space be different than 377 ohms because of that too?
I once had a physics professor who said that not only would he be working in units where hbar == h/(2*pi) was equal to one, he was also going to be using units where h, 2, and pi were all individually equal to one :-).
Tim.
Hmm. c = 1.8*10^12 furlongs per fortnight. Looks OK to me.
I wish my stomach could fit fourty million pies, but I usually eat only a third pi at a time instead.
(Note that 1 pie = 2pi radians.)
Tim
-- Deep Fryer: a very philosophical monk. Website:
The 4 * pi * 10^-7 was either chosen arbitrarily, or there were other arbitrary choices made elsewhere in the SI system of measurements that resulted in that value being what it is.
To set them to one you say "u_o = 1" and "e_o = 1". Then you deduce that C = 1 must be true. Now you arbitrarily pick either a time or a length measure, and the other one is fixed. With your measures of length and time in hand you know all you need to know for you measures of inductance and capacitance, and therefore charge, electromotive force, and current. I suspect that you'll have force in there too, which means that mass won't be far behind. Keep going, and pretty soon you'll have your own system of measurements to rival the SI system; then you'll just have to find names for them -- I'd like to reserve "Wescott" for inductance, in honor of all of the folks who think I'm loopy.
Hi,
I was reading through the ARRL uhf/microwave experimenter's manual and came across this formula for the propagation velocity in a transmission medium:
v = 1/sqrt(LC)
and substituting the values for L and C for free space:
v = 1/sqrt(ue) where u and e are permeability and permittivity
u= 4*pie*10^7 (H/m) e= (1/36)*pie*10^9 (F/m)
So does the value of pie determine the speed of light in free space or am I reading this wrong? Also I have read that the characteristic impedance of free space is 120*pie from this formula:
Z = sqrt(u/e)
This info is in chapter 5 pages 6 and 7.
cheers, Jamie
I read in sci.electronics.design that Jamie Morken wrote (in ) about 'free space as a transmission medium', on Wed, 2 Nov 2005:
You are not reading it wrong. But pi is not the only dish on the menu. Apart from pi there are the numerical values 4 x 10^-7 and 36 x 10^9. No-one knows why these numbers are what they are (apart from depending on the units of measurement we use), and that bugs current physicists a LOT!
It's possible to devise a system of units in which both numbers are 1, but you wouldn't like it.(;-)
Yes, it is 377 ohms.
Not sure what you mean, how can you set them to 1?
cheers, Jamie
No, they are both determined by the Fundamental Nature of Reality. :-)
[I presume that when you say, 'pie', you're talking about 'pi', the ratio of the circumference of a circle to its diameter? - thanks!]I read in sci.electronics.design that Jamie Morken wrote (in ) about 'free space as a transmission medium', on Wed, 2 Nov 2005:
Choose your units of length, mass, time and electric charge to make them
I read in sci.electronics.design that Tim Williams wrote (in ) about 'free space as a transmission medium', on Wed, 2 Nov 2005:
But the ratio of circumference to diameter of a large member of the gourd family is pumpkin pi.
"John Woodgate" a écrit dans le message de news: snipped-for-privacy@jmwa.demon.co.uk...
Also note that 1 pea = 4 pi steradians
Yes, I meant pi really :)
Thanks all for the humorous and inductive/loopy answers.
cheers, Jamie
Greetings, Jamie. The confusion comes from the fact that e0 =~ 8.85419 * 10^12 [F/m], which is very close to (1/36) * pi * 10^10 [not (1/36) * pi * 10^9] (an error of roughly 1.4 %). The same is true for the impedance of free space. It is simply VERY close to 120 * pi, but not quite right on.
Mario Chenier
Can we talk about geography now? I'm getting Hungary.
Ok so after you deduce C = 1 is true, then you pick a time or a length measure..? So velocity=distance/time and I set distance to 1meter, then time is equal to 1second.. so we need to redefine how long one second is and/or how long 1meter is so that it matches up with the actual speed of light? I guess that this is what you and John are talking about, or am I missing something more obvious? I occasionally have a thick skull so this would be no surprise :)
cheers, Jamie
-- I'd like to reserve "Wescott"
I read in sci.electronics.design that Jamie Morken wrote (in ) about 'free space as a transmission medium', on Fri, 4 Nov 2005:
No, abandon 'second' and 'metre' and give the new units new names, such as 'Jamie' and 'Morken'. (;-)
If you want to alter pi you need to alter the geometry of space.
Yes, and the energy demands are horrendous. So don't try it at home!
Well, horrendous using known methods. I suspect there may be easier ways that making black holes.
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