Re: Sparks

[brian whatcott <inet@intellisys.net>]

A charged body will shed excess charge if it can. But air, particularly dry
air
is an excellent insulator - so much better than the (soft) vacuum.
 If you gain enough charge from the carpet, your hair will certainly
indicate, electrometer style, that it is laboriously emitting some.

In an experimental context, it is found that the shape of the electrodes
has a marked effect on the breakdown gap needed. Needle points which
provide the most concentrated field initiate discharging over wider gaps
than big round balls, which retard ionization.

And (here I sincerely hope I am not telling you more than I in fact know...)
a sharp point and a ball point for electrodes show some directionality to
high voltage spikes of opposite polarity...

 In a practical vein, technicians silenced noisy EHT leads in TVs and
Radars by resoldering sharp spurs to rounded contour.

Brian Whatcott


At 17:00 9/4/98 -0400, Ed Schweber wrote:
> ... rubbing your feet along a carpet will cause an excess of
> electrons to accumulate on your body, to concentrate on thin objects like
> your fingers, and when you reach for a metal  door knob the mutual repulsion
> between the electrons causes some of them to jump across the gap forming the
> spark.
>
>   In one of those obvious questions no one has asked me before until today,
> a student wanted to know why the door knob was necessary. Why don't the
> electrons just leave your finger due to their repulsion whether or not the
> doorknob is nearby.
....
>    What if your walking along the carpet created an electron deficit of the
> same magnitude on your finger. Your finger would then attract electrons from
> the door knob but it would seem that there wouldn't be any additional
> inductive effect and therefore it is less likely that a spark would jump. Is
> this also the case.
>
>   Thanks for any input.
>
> Ed Schweber

brian whatcott <inet@intellisys.net>
Altus OK