Re: Experiment - Displacement Current's Magnetic Fields

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Malcolm Watts by way of Terry Fritz <twftesla-at-qwest-dot-net>" <m.j.watts-at-massey.ac.nz>

Hi Paul,

On 13 Mar 2002, at 8:00, Tesla list wrote:

> Original poster: "Paul Nicholson by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <paul-at-abelian.demon.co.uk>
> 
> I wrote:
> > Reliance on belief is nearly always fatal for
> > progress - Malcolm's ruler, ...
> 
> Malcolm wrote:
> > I hope a crude and early attempt at modelling the resonator
> > through a mechanical analogy is not taken by anyone as a
> > doctrine.
> 
> Well I didn't mean to suggest that the flexing ruler analogy was
> cranky or doctrine, but it works well as an illustration of how
> these beliefs become established. The ruler voltage profile would
> not have passed some fairly basic sanity checks, yet it was
> beginning to find itself used as an input assumption in computer
> programs, etc, in a way similar to the use of 1/4 wave wire length
> and DC inductance in Fres calculations, which become established
> simply by going unchallenged.
> 
> If you need a voltage profile and you don't have one, you have no
> choice but to guess one.  This often happens in physics and you just
> have to do the best you can to qualify your guess with whatever
> cross checks that you can.
> 
> In the case of the ruler analogy, the rising voltage gradient 
> towards the top of the coil is immediately suspicious, since it
> implies not only a lot of current in that part of the coil (which
> is incompatible with a reasonable guess at the capacitance profile),
> but also implies a vastly increasing coil current as you approach
> the top, which defies explanation.  A safer and justifiable guess
> would have been a sine.

Perhaps it might be more accurate to say that the degree of bend per 
unit length gives a fair indication of the dV/dx profile. I wonder 
how closely that follows observation for the fundamental case? Quite 
closely I'm willing to bet.
     If we are otherwise talking about absolute displacement, then I 
can do nothing but agree with you.

Regards,
malcolm