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Re: [Phys-l] Electrocution in Bathtub - Hollywood style



Scott;

The next time you do this, could you please video tape it and make it available (for example http://www.youtube.com/)? I think this would be of general interest (call me chicken but I'm probably not going to try it myself).

I also would encourage you NOT to let students do this. What happens if someone panics at feeling the tingle, takes their hand off their head and grabs something nearby .....?

kyle

Message: 8
Date: Wed, 17 Oct 2007 15:36:14 -0400
From: Scott Goelzer <s.goelzer@comcast.net>
Subject: Re: [Phys-l] Electrocution in Bathtub - Hollywood style
To: Forum for Physics Educators <phys-l@carnot.physics.buffalo.edu>
Message-ID: <7A4ACFBC-E04A-4957-8567-BEDEF472E129@comcast.net>
Content-Type: text/plain; charset=US-ASCII; delsp=yes; format=flowed

A demo can be set up to help feel this on a small scale.

Probably catch some negative comments, but during my internship I was
taught a demo that I now call the electric fish tank of death.
Dramatic and effective.

Set up 10-20 gallon tank filled halfway with fresh water.

Stand metal plates at each end and attach the hot and neutral of 120V
AC line voltage to the plates through a GFI. Alligator clips work fine.

Place left hand on top of head and leave hand there while tank is
plugged in.

Use an AC field sensor to show that the water is 'live' - no
Hollywood sparking blue fire steaming water.

Standing on a non-grounded floor with rubber shoes, insert two
fingers (of the right hand!) into the water keeping the fingers
together. The AC sensor will show that you are now 'live'. Do not
lean on the tank, counter or contact anything else. Students are
stunned at your continued existence.

Separate the fingers into a inverted peace sign configuration with
the tips of the fingers wet and parallel to the metal plates. (left
hand still on head - or in pocket). No tingle since no potential
difference.

Repeat with the fingers perp. to plate. Tingle grows with separation.
Painful if hangnails or cuts.

Other demos:
Connect a test wire to ground and drop in tank - GFI trips.
Connect two wires to a bulb and mount on a compass-like (the drawing
kind) rig to show when the bulb will light when it will not. Mine is
made from two rulers fastened on one end with the wires running down
the rulers. Use in place of fingers for the faint of heart.
Discuss how putting a finger from each hand into the water will NOT
trip the GFI and WILL place a current across the heart.
unplug the plates and drop a incan. bulb in. Plug the bulb in. Try it
with a sacrificial hair dryer - it runs underwater just fine.


It's not called the fish tank of death for nothing. Extreme care must
be taken, but no more relative danger than if one were using a
tablesaw. I let students volunteer to do this with direct
supervision. I think they take more of a hit from the trick shocking
pens they keep bringing to school - those really hurt.

I have always wanted to see if a fish would learn (quickly) to swim
parallel to the plates, but that seems too cruel.

As to the bathtub, I would not like be in a tub with a grounded drain
and my body between an appliance.

Scott



**********************************
Scott Goelzer
Physics Teacher
Coe-Brown Northwood Academy
Northwood NH 03261
603-942-5531e218
sgoelzer@coebrownacademy.com
**********************************



--
------------------------------------------
'Violence is the last refuge of the
incompetent.'
Issac Asimov

kyle forinash 812-941-2039
kforinas@ius.edu
http://Physics.ius.edu/
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