Re: Magnetic Field in a Flat Spiral

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

Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-qwest-dot-net>" <jimlux-at-earthlink-dot-net>

More likely that humidity (absolute) and temperature affect the loss of the
form on which the coil is wound...

The dielectric constant of air wouldn't change all that much as a result of
changes in humidity... Just not much mass there to change things..
(certainly not in the area of several percent).

Dimensional changes in the coil shape and size could result in changes..
However, mechanical temperature coefficient for metal is a few ppm/degree
and wouldn't have an effect of percent.  Cardboard and plastic on the other
hand could have substantial changes in dimensions for fairly small changes
in temperature and (more importantly) humidity.

Surface resistivity (which is strongly affected by humidity) would also
affect Q.  In the historical Tesla case, he was using things like gutta
percha and fiber (cotton or silk) insulation, all of which are very
environment sensitive.  


Tesla list wrote:
> 
> Original poster: "rheidlebaugh by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <rheidlebaugh-at-zialink-dot-com>
> 
> It appears the humidity is probibly changing the dialectric constant and the
> resistance of the air. In a flat coil you are subject to the capacitive
> effects of the surounding air in both I and E aspects of the air return
> capacitive aspects of the surounding field. While the temprature is changing
> the L of the coil itself (expansion and contraction of the coil) this effect
> should be low.Tesla found that temprature had a great effect on the tuning
> of a flat coil This should NOT have a great effect on the Q of the coil its
> self, only the tunung curve. Each test should have corrected for this.
>   Robert  H
> 
> > From: "Tesla list" <tesla-at-pupman-dot-com>
> > Date: Sun, 10 Mar 2002 20:28:44 -0700
> > To: tesla-at-pupman-dot-com
> > Subject: Re: Magnetic Field in a Flat Spiral
> > Resent-From: tesla-at-pupman-dot-com
> > Resent-Date: Sun, 10 Mar 2002 20:29:55 -0700
> >
> > Original poster: "Malcolm Watts by way of Terry Fritz <twftesla-at-qwest-dot-net>"
> > <m.j.watts-at-massey.ac.nz>
> >
> > Hi Jim,
> >
> > On 10 Mar 2002, at 17:23, Tesla list wrote:
> >
> >> Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-qwest-dot-net>"
> > <jimlux-at-earthlink-dot-net>
> >>
> >> The variation in resistance just due to temperature might have a
significant
> >> effect on Q, even though the temperature variation isn't much. Let's
see...
> >> tempco of copper is something like 0.004 per degree (C).., I think.  A 10
> >> degree change will result in a 4% change in DC resistance...  It will also
> >> affect the skin depth, so the effect might be more than that....
> >>
> >> It might also be 0.0004, in which case, we're looking at fractions of a
> >> percent..
> >
> > Yes, but doesn't copper have a positive tempco? In which case, had
> > that been the influencing factor, I should have scored a higher, not
> > lower Q on the second day? And if that's so, then humidity appears to
> > be having a greater effect than I had previously suspected?
> >
> > Regards,
> > Malcolm
> >
> >> ----- Original Message -----
> >> From: "Tesla list" <tesla-at-pupman-dot-com>
> >> To: <tesla-at-pupman-dot-com>
> >> Sent: Sunday, March 10, 2002 2:28 PM
msnip...