Re: [Phys-l] Sparks

[Bernard Cleyet <bernardcleyet@redshift.com>]

Chuck!

I don't think the molten metal is the spark, as I wrote in my second  
post of May six, the spark is a transient discharge.  the molten  
metal is the tip of the electrode that failed to vaporize and then  
ionize.

Not incidentally this is similar to the mechanism* of the sparking  
initiated by the intense heating of the thin Al coating on a CD or  
DVD by the microwaves in an oven.  The circular paths are due either  
to the metal being thinner there, flaws, cracks, etc; or the heating  
greater because of differences in the dielectric backing.  Bill Beaty  
studied similar sparking due to high current densities in thin carbon  
film resistors, wherein the spark occurred at slight differences in  
thickness, cracks, etc.


Beaty referred me to this similar study:

http://ijd.sagepub.com/cgi/content/abstract/10/3/195



* which I proposed independently in a thread on, was it microwave  
mischief?


bc

p.s. Yes, if you refer to the sparks and not the droplets.  If the  
current were not limited by the increased path length, the spark  
would be continuous, and, therefore, called an arc.



On 2008, May 26, , at 08:19, chuck britton wrote:

> These low voltage, high current sparks are molten, burning droplets
> of metal that follow parabolic trajectories.
> Same as July 4 sparklers.
>
> Is it right to compare these to high voltage, low current sparks
> which are ionized atmosphere, plasma?
> Miniature lightning bolts?
>
>
> On May 25, 2008, at May 25(Sun) 9:29 , John Denker wrote:
>
> > Here's a fun experiment you can do.