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On 05/06/2008 04:08 AM, Joseph Bellina wrote:
The same explanation works for why you don't feel a "shock" from
static electricity if you hold a metal object in your hand and touch
something that is grounded. The "shock" is actually local heating of
your skin caused by a relatively high current density at the point
where you skin is close to the grounded object. If you hold a metal
object, like your car key, creates a large area of contact and hence
a low current density, and no sensation of shock.
That depends.
In addition to heating, there is also direct electrical stimulation
of the nerves. Ben Franklin was fond of setting up a parlor trick
where a line of N persons would hold hands, and the two persons at
the end of the line would each grab one terminal of a a Leyden jar.
Everybody would get zapped. I don't think you can attribute that
to heating.
=====================
The whole story about arcs and sparks is exceedingly complicated.
For those who want more info, here are some starting points:
http://www.google.com/search?q=corona+field+ions
http://www.google.com/search?q=dielectric-breakdown
http://www.google.com/search?q=space-charge
http://www.google.com/search?q=arc-suppression
http://www.google.com/search?q=lightning
There is a lot of good physics in this, and plenty of applications,
for instance:
-- high voltage / high current switchgear, such as you find at
power plants and substations.
-- tandem van de Graaf (a nice piece of large-scale lab equipment)
-- Geiger-Müller tubes
-- spark chambers for high-energy physics
-- lightning arrestors, such as they attach to phone lines
-- et cetera
Tangentially related is dielectric breakdown in /solids/, which
has additional zillions of applications.
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