ODP: one for the theorist

[Roman Sowa]

> Od:	Martin Czech [SMTP:martin.czech at intermetall.de]
> Wysłano:	13 lipca 1999 17:59
> Do:	synth-diy at mailhost.bpa.nl
> Temat:	one for the theorist
> 
> I've recently read a book where the inductance of a single piece of wire
> was given. This is strange, I thought, because you can only speak of the
> inductance of a loop. And, after all what I know, the magnetic energy
> of a single wire without "back" current path goes towards infinity and
> so does L. 
	[Roman Sowa] 
	Current flowing through every wire causes magnetic field around it.
	H file lines are circles around the wire. When current changes,
	the H file also changes, so you basically change H file energy
	which is what inductors do. Btw, the E file also appears then, but
	that's a whole different story. When wire is looped, H vectors
	are summed inside the loop, thus bigger H energy.
	BTW, have you seen UHF transformers in an old TV set maybe?
	Those are few straight wires in paralel. 


> Example:
> 
> If you have a cylindric shaped wire then H=i/(2*PI*r).  The magnetic
> flux will be phi=u*l* int{H(r)dr}
> 
> = i*u*l/(2*pi)*ln(r/r0)
> 
> (u=my, r0 radius, r distance)
> 
> The total flux will need r->infinity and this is clearly also infinite,
> thus the inductance is also infinite.
	[Roman Sowa]  
	You answered your question yourself - this equation is valid only
	for 'cylindric shaped wire' which is simplifed case of all those
	Maxwell stuff.

> This makes sense, you simply need the back current path to have finite
> flux.
> So, is this a stupid book, or is it me who is the stupid?
	[Roman Sowa]  
	No, your'e not stupid. I think all this electromagnetic stuff wasn't
so
	mysterious if E and H vectors would be visible. But then we couldn't
	see anything else in this rf poluted world.