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Re: [Phys-l] Chimp unsuccessfully hangs from high voltage line



When I was young, our electric fence consisted of a 6-volt battery (dry
cell) attached to the controller. The shock received by touching the
fence was annoying, and somewhat of a surprise if done by accident, but
really no big deal. Us kids would form a line, holding hands, one end
of the line would grab the fence, and the poor unsuspecting (younger and
inexperienced) person on the other end always seemed to get the biggest
jolt. It seemed as if the current passed from hand to hand, rather than
from hand to foot -- except for the end person who experienced the full
hand to foot effect. This is the way I remember it, but it does not
agree with my physics analysis where I would expect the circuit to
resemble a parallel circuit where the effect should be divided (and
diminished) somewhat equally.

One problem we had was as the vegetation grew, sooner or later a weed of
some type would contact the fence, shorting it out -- or at least
greatly diminishing the shock. This was bad news as we were then
chasing cattle back into the pen. We regularly walked the fence to be
sure it wasn't being grounded in some way.

Then came a wonderful enhancement -- it was called a "weed chopper."
This consisted of an electric fencer that was plugged into the wall
outlet. As weeds grew, and touched the fence, the higher power would
burn them off -- hence the name "weed chopper." This brought a quick
end to our game of grabbing the fence with a line of kids. I have a
number of incidents, permanently burned into my mind (and body) of
experiences with the new fence.

Oren Quist
South Dakota State University



-----Original Message-----
From: phys-l-bounces@carnot.physics.buffalo.edu
[mailto:phys-l-bounces@carnot.physics.buffalo.edu] On Behalf Of Warren
Hein
Sent: Sunday, August 27, 2006 10:11 AM
To: Forum for Physics Educators
Subject: Re: [Phys-l] Chimp unsuccessfully hangs from high voltage line

When I was growing up on a dairy farm some very long time ago, we used
electric fences to separate pasture lots, corn fields etc. I remember
one time we let the new yearling calves out and one of them ran into the
fence and got tangle up, was laying on the ground and jolting with the
pulsating electric shock. My dad went over and grabbed her, trying to
help her get off-not a good thing to do before turning off the voltage
source. Painful but not fatal.

Warren

"Matt Coia" <matt.coia@gmail.com> 8/27/2006 9:36 AM >>>
I seem to recall using long grass blades to "test" to see if a fence
was
on. By using the grass as an insulating buffer between your hand and
the
fence, you can minimize the jolt to a light tingle in a live wire. Of
course, I've had my share of full jolts, too! :)

Matt


On 8/26/06, Brian Whatcott <betwys1@sbcglobal.net> wrote:

At 07:45 AM 8/26/2006, Joe, you wrote:
Some years ago, I had a crazyish uncle who had a small resort in
the
Catskills, and decided it would be fun to have a chimp to entertain
the guests. While as it happened, one day the chimp got away. Now
this "resort" was in the middle of cow pasture country, a very
lovely
setting with pastures separated by electric fences...a single wire
with some high voltage on it. There was enough internal resistance
in the power supply so that animals got shocked by not killed.
///
Joseph J. Bellina, Jr. Ph.D.


I have lately developed a personal interest in electric fences.
During a hot Summer, when grass easily burns out, horses are tempted
to reach through wire to the greener grass on the other side.
If that wire is barbed, they cut ears, shoulders, legs etc., in
reaching
through. Unlike cattle, they are said to be slow to learn from
their
cuts.

Horse owners like to place an offset electric wire, to keep them
back.
The ordinary sort of fence charger resembles an induction coil,
which
pulses the fence wire with a high voltage pulse.
(Some are apparently configured like a transformer, instead)

The source impedance is high enough to avoid permanent injury to
animals. But this leads to a problem. The grass that is no
longer
nibbled, grows to touch the wire, and this can easily emasculate
the pulse.

A recent approach to fence charging takes a different tack: a high
voltage pulse is still generated, but now, its output is lower
impedance.
Instead, its duration is limited in order to avoid injuring the
quadrupeds. These are billed as "Low impedance" in that they are
not disabled by moderate grass/weed loading.
Chargers are also rated by pulse energy:
0.1 J to 1.5 J are to be seen in the feed store.



Brian Whatcott Altus OK Eureka!


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Forum for Physics Educators
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_______________________________________________
Forum for Physics Educators
Phys-l@carnot.physics.buffalo.edu
https://carnot.physics.buffalo.edu/mailman/listinfo/phys-l
_______________________________________________
Forum for Physics Educators
Phys-l@carnot.physics.buffalo.edu
https://carnot.physics.buffalo.edu/mailman/listinfo/phys-l