Re: Power Lines

[Rick Tarara <rtarara@SAINTMARYS.EDU>]

While not as colorful, I always present the following which is taken from an
old textbook by Marion.
These are hand to foot currents lasting at least 1 second.

Current/Effect
0-0.5 mA         none

0.5-2 mA         Threshold of feeling

2-10 mA         Pain; muscular contractions

10-20 mA         Increased muscular effect, some injury; above 16 mA is the
'let-go' current above which a                         person cannot release
held objects.

20-100 mA     Respiratory paralysis

100 mA -3 A     Ventricular fibrillation; fatal unless resuscitation occurs
immediately.

above 3 A         Cardiac arrest; heart can be restarted if shock is very
brief; severe burns

Now you can calculate the current for 120 volts for a dry body at 100,000
ohms and for a wet body at about 1500 ohms.

Rick

----- Original Message -----
From: "Richard Blade" <rblade@UCCS.EDU>

> Tina, Rick, et al-
>
> This is my first time to respond to the list, so I hope my contribution is
> of some value.
>
> In my intro physics class, I introduce the conceptual basis of electrical
> current in the "Blade Scale" that was developed by my brother Bill while
in
> high school.  It relates magnitude of current to the electrical shock
> effect on the human body through a set of desciptive nouns:
>
> bite=1-10ma
> zap=10-100ma
> scutch=0.1-1amp
> sizzle=1-10amp
>
> It seems to be a very useful tool in introducing the students to electric
> circuits.  Incidentally, voltage (i.e. electric potential difference) is
> introduced as a kind of pressure that pushes the current through
> conductors.  Resistance in the context of electrical shock has to be
> carefully treated because biological materials are often nonlinear and
> almost all the resistance in the human body is in the skin, so probes
> placed between different points on the body have roughly the same
> resistance between them, independent of distance.  The latter provides a
> good question for discussion by the class.  Usually students begin by
> thinking about salty sweat, but someone eventually gets it after
> considering the conductivity of the blood.  That leads to the introduction
> of the "principle path method" of analyzing circuits, which, in contrast
to
> Kirchhoff's laws, allows the studenst to conceptualize what is actually
> going on in a complicated circuit.
>
> Richard Blade