myers@hpfcdj.HP.COM (Bob Myers) (01/29/91)
>To clear up: > 1) Voltage is analogous to pressure. > 2) Amperage is analogous to flow rate. > 3) WATTAGE is analogous to force. Not exactly. "Wattage" is, as you may recall, NOT analogous to force but IS an expression of *power*. Voltage - more precisely, electric potential - IS a force. Ever hear the phrase, "electromotive force?" And note that you distinguished "pressure" and "force" in the above; exactly how do you distinguish these? In any event, it is not the power level that kills, exactly - unless you're concerned about killing the subject via internal heating. The question is the level of *current* which will interfere with the heart's natural "control signals." Long before there is any actual damage to the tissue due to electrical effects (heating), the heart has "lost sync" and the subject is (or very soon will be) dead. My, but this is a cheery string, isn't it? :-) Bob Myers KC0EW HP Graphics Tech. Div.| Opinions expressed here are not Ft. Collins, Colorado | those of my employer or any other myers@fc.hp.com | sentient life-form on this planet.
brendan@otc.otca.oz (Brendan Jones) (01/29/91)
Talking about using the human body as a conductor...
I once saw a little 10 minute film made in the '50s late at night on TV.
The film was actually about religion, but to make a point, the narrator
made a most remarkable demonstration.
In the studio, they had a Van Der Graff generator (I think), a horizontal
circular anode that acted as a platform and about three metres above that
a pointed cathode.
The generator was said to deliver 1 million volts EMF at a frequency of
20 kHz. The narrator then put on pointed thimble caps on the ends of
each finger (to prevent corona discharge burning the ends of his fingers),
grabbed a bit of 4x2, stood on the anode, and held the wood up to the
cathode.
The million volts arced across from the wood to the cathode (a distance of
about 20 cm) and the wood burst into flames. All the while, he was talking
and making some deep and meaningful observations.
So it goes to show that EMF is not the killer. Current is, but obviously
the body is a low pass filter and must have high attenuation at 20 kHz.
So what is the 3dB rolloff? I suspect around 100 Hz which is why 50 Hz
is such a killer.
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In article <2204@otc.otca.oz> brendan@otc.otca.oz (Brendan Jones) writes: **stuff deleted** >In the studio, they had a Van Der Graff generator (I think), a horizontal >circular anode that acted as a platform and about three metres above that >a pointed cathode. > >The generator was said to deliver 1 million volts EMF at a frequency of >20 kHz. The narrator then put on pointed thimble caps on the ends of **stuff deleted**.... A Van de Graaf generator is DC. What you saw was almost certainly a Tesla coil. This sort of demonstration was common before WW1. **stuff deleted** >So it goes to show that EMF is not the killer. Current is, but obviously >the body is a low pass filter and must have high attenuation at 20 kHz. >So what is the 3dB rolloff? I suspect around 100 Hz which is why 50 Hz >is such a killer. What was demonstrated was the "skin effect", where at high frequencies, current tends to flow on the outside of the conductor only. Hence the nervous system is not affected, and so the person is not electrocuted. Get the power density up and you'll cook though; just ask any HAM operator about RF burns. D
johne@hp-vcd.HP.COM (John Eaton) (01/31/91)
<<< < The same is valid with electricity. In fact comparisons with water < are used in some classes of Junior High School, in order to make < electricity less abstract. You can explain batteries, resistance < and condensators, just by comparing with water phenomenoms. ---------- And in some plumbing schools they teach everything in terms of wires and switches. It makes plumbing less abstract. :) John Eaton !hp-vcd!johne