On 1/8/12 7:11 AM, Carl Noggle wrote:
The Lichtenberg figure forms often when sparks slide over the surface of a dielectric. It is typical of dendritic figures that form when water or some substance has to spread out (or be collected from) a surface (or in the case of Bert Hickman's figures, or tree roots). In this case, charge has to be distributed. If the dI/dt is fast enough, the high dielectric constant of the water in the body will dominate over the resistivity and the current will flow over the surface. dI/dt can be as high as 10E11 amps per second in the vicinity of a lightning strike. This is probably why only about of 10% of lightning strike victims die. Power line electrocutions, however, are very often fatal, since the dI/dt is much slower and the current can flow into the body. This is basically a skin depth argument in the time domain and applied to a very lossy dielectric. We would not expect figures on the skin of a power line electrocution victim.
So it's a transient effect driven by rise time. Interesting. Lightning caused Lichtenberg figures occur on non-human substrates as well.
Here's a TC list question about which I've been wondering... Would such a figure occur with an ordinary HV incident (e.g. contact with a power line). Or would it have to be pulsed power with very high peak current/voltage? Lichtenberg figures are similar to the dendritic treeing that occurs in dielectric, but not from the same cause, as far as I know (and treeing is a long duration aging kind of effect), although the fractal nature IS similar (and for the same reason.. field distributions) _______________________________________________ Tesla mailing list Tesla@xxxxxxxxxx http://www.pupman.com/mailman/listinfo/tesla_______________________________________________ Tesla mailing list Tesla@xxxxxxxxxx http://www.pupman.com/mailman/listinfo/tesla
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