[ExI] And Meta You Know

[hkhenson]

At 08:49 PM 1/24/2008, you wrote:

>--- hkhenson <hkhenson at rogers.com> escreveu:
>
>
> > You still get a reflection in the heavy rope.  In
> > the limiting case,
> > with a zero mass per unit length rope in the small
> > rope, it all
> > reflects.  This is the equivalent of a open
> > transmission line.  You
> > can simulate this by tying a rope to a free sliding
> > ring on a pole
> > and launching a vertical wave down the rope.
> >
> > Keith
> >
>
>I see.. so the difference between the reflections
>(free ring/fixed ring-building wall)would be that one
>"inverts" the wave? or.. the wall 'absorbs' it?

Inversion is correct.  Neither "open" nor "shorted" absorbs the wave, 
they both totally reflect, though with different phases.  The only 
way you get the wave to be absorbed would be with a friction damper 
matched to the rope.

Electrical transmission lines come a variety of impedances.  Signals 
are absorbed without reflection when they are terminated with a 
matched resistor.  Old flat TV antenna cable is 300 ohms, coax is 
typically 50 or 75 ohms.  The Cat 5 cable that probably connects your 
computer has several twisted pairs of wires that are about 110 ohms.

Keith