one for the theorist

[Daniel Gendreau]

> 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.
>
> Contrary a normal twisted pair arrangement makes sense.
...
> So, is this a stupid book, or is it me who is the stupid?
> m.c.

Neither... Obviously you are not stupid because you had the sense to notice
this stuff,
But Remember... infinite is a theoretical term. In reality, nothing is
infinite.

IE. A wire never has 0 resistance, 0 capacitance and 0 inductance as we like
to pretend. It may be a rediculosly small ammount, but it is there.


Whenever i think about this stuff I always like to go back to the water
analogy I was taught with. Wires are like pipes, voltage is water pressure
and current is water in motion.

Inductance in this analogy is like the momentum of the water and its
reluctance to accelerate or decelerate.
No matter how you set up your circuit, the water will always be reluctant to
speed up or slow down. You are always going to have some momentum. Even if
you consider it to be negligible.

Resistance is like the size of the pipes. Thus, no matter how big you make
your pipes, they will always impart some resistance to the flow of the
watter and cause pressure (voltage) to build up. Even if you consider it to
be negligible.

-Dan G.