Re: [Phys-l] Sparks

[Bernard Cleyet <bernardcleyet@redshift.com>]

Huh?

A solid material may emit light if at "incandescent temperature.  If  
the spark is "white" it likely is a plasma as at such a colour temp.  
most oxidizable materials are burning.

bc doesn't think solids "burn"  they rust.

p.s. perhaps there is confusion about: discharges, arcs, and sparks.   
Harnwell defines sparks as transitory discharges due to current  
limiting resistance.  He also gives the formula:

E(crit.) = A* rho [ 1 + B/ sqrt{ rho*R}]

where E is the critical surface field, A & B constants, R radius of  
curvature of the electrode (The other is flat?).  For air @ 25 C, A *  
rho is ~ 30kV/cm and B / sqrt (rho) ~ 0.3  [Loeb, Rev. Mod. Phys., 8,  
267 (1936)  then:

Summarized:  If any radii are small in comparison to the separation  
the spark breakdown is preceded by tentacular brush or tree like  
discharge from the regions of greatest field, called corona,  and  
much more including G-M tubes, etc.


On 2008, May 06, , at 16:23, Joseph Bellina wrote:

> Most high current density "sparks"...they may not be high current,
> and they may not spark, are plasmas rather then solid material.
>
> joe
>
> Joseph J. Bellina, Jr. Ph.D.
> Professor of Physics
> Saint Mary's College
> Notre Dame, IN 46556
>
> On May 6, 2008, at 6:02 PM, chuck britton wrote:
>
> > JD makes the point about 'high' voltage sparks vs high current  
> > sparks.
> >
> > Also note that each high current 'spark' follows a parabolic path, as
> > do the 'sparks' from July 4th 'sparklers'.
> >
> > Hot metal droplets 'burn' as they fly through the air.
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