Re: Spark length dependence on air pressure.

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Gerry  Reynolds" <gerryreynolds@xxxxxxxxxxxxx>

Hi Jim,

If you get your hands on a pilots slide rule, you can easily calculate 
"density" altitude using temp and barametric pressure (temperature 
corrected to sea level - what the weather man or your local airport 
reports) for your elevation.  Density altitude would be the equivalent 
altitude that has the same density at standard temp and pressure as your 
site at non standard temp and pressure.

Gerry R.


> Original poster: Jim Lux <jimlux@xxxxxxxxxxxxx>
>
> > His 7.7 km number may be more accurate than my 7 km number.  Would need
> > to check.
> > Another complication is that pressure also depends on temperature, which
> > varies with height also, and so the pressure
> > falloff with height is slightly different than for density.  But density
> > is the more fundamental parameter for breakdown, because it controls the
> > mean free path of the electrons, and it is over these mean free paths
> > that they gain enough energy to ionize.
>
> Excellent point.  I did use pressure to get my 7.7 km, and he's right, 
> density is the controlling thing.  Assumed lapse rate (temperature profile 
> as you change in altitude) also affects it, because you're basically 
> integrating.  I just used ICAO standard atmosphere.