Re: Newbie - Voltage - shock of 9v battery vs. 12v car battery

In article <1130881193.576353.13790@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>,
hdjim69@xxxxxxxxxxx says...

> I guess I still don't see where the big difference is. Voltage is
> pressure (or potential pressure) or the amount of EMF. The more force,
> the more electrons will flow so the more current or amps there will be.
> The resistance of the human body will be the same for both batteries.
> So why is it, one can be literally tortured with a 12v battery but not
> with a 9v ? The amount of current difference due to the 3v difference
> can't be enough to make one battery a torture device and one a toy.

Hmmm... Methinks you've been watching one too many old
'Pretender' episodes. ;-)

The reason Hollywood likes to use car batteries in their phony
"torture" scenes is because they look big and impressive, and because,
when the ends of whatever cable they're using are brushed together, it
makes a very impressive (to the untrained eye) spark.

The human body presents a typical skin resistance, hand-to-hand,
of over 250,000 ohms. I suppose this might drop down to a few thousand
ohms if you're soaked to the skin with salt water.

Just for the sake of argument, let's say your skin resistance
drops to, say, 2500 ohms hand-to-hand if you're soaking wet (which is a
drop of two orders of magnitude in this context).

Using Ohm's Law, and taking 12V over 2500 ohms, I come up with a
total current flow of 0.0048 amps, or 4.8 milliamps. Under normal
conditions, with dry skin and assuming 250k ohms, the max current
possible with 12V is about 48 microamps.

Considering that the "danger" threshold across the chest is at
least 20 milliamps, I don't see how a 12V car battery could possibly be
harmful, or even felt, at either amount of current. According to some
further number-crunching, you'd need to up the voltage to between 48-50
to get anywhere close to dangerous.

So, in summary: If you just got out of the ocean, and you
immediately go work on things in a telephone central office (where the
standard voltage is around -52VDC), yes, you could be setting yourself
up for some problems.

Outside of that, it's just Hollywood messing with your gray
matter.

Keep the peace(es).


--
Dr. Anton T. Squeegee, Director, Dutch Surrealist Plumbing Institute.
(Known to some as Bruce Lane, ARS KC7GR,
kyrrin (a/t) bluefeathertech[d=o=t]calm -- www.bluefeathertech.com
"If Salvador Dali had owned a computer, would it have been equipped
with surreal ports?"
.

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