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



A current of 100 mA or more is likely to be fatal. In the 100-3000 mA range it is because of the onset of ventricular fibrillation which does not cease when the current is removed. Above that it is cardiac arrest. The wet body can have a resistance 100 times lower than a dry one (falling from 100,000 ohms--hand to foot--to maybe 1000 ohms.) Thus 115 Volt power can produce lethal currents in a wet body.

If the wet person grabs onto a 1500 Watt hair dryer and effectively puts themselves in parallel with the internal resistance (around 10-12 ohms), then the current through them is a bit above 100 mA and likely fatal.

With the object falling into the tub, the person would still be (I think) effectively in parallel with the lowest resistance path which would be the water now directly connecting the two sides of the AC line. Don't know what that resistance might be--let's say 1 ohm and therefore 115 Amps are drawn (very briefly before the breakers go). But if your 1000 ohms is in parallel with 1 ohm but you have 115 amps of current through the low resistance path, you still get about 100+ mA through you.

So, it looks dangerous to me. I don't want to run the experiment.

Rick

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Richard W. Tarara
Professor of Physics
Saint Mary's College
Notre Dame, IN
rtarara@saintmarys.edu
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Free Physics Software
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www.saintmarys.edu/~rtarara/software.html
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----- Original Message ----- From: "Fakhruddin, Hasan" <hfakhrud@bsu.edu>
To: "AP Physics" <ap-physics@lyris.collegeboard.com>; "Forum for Physics Educators" <phys-l@carnot.physics.buffalo.edu>
Sent: Wednesday, October 17, 2007 9:41 AM
Subject: [Phys-l] Electrocution in Bathtub - Hollywood style


Hi!

I have seen this in at least three Hollywood movies; electrocuting
someone in a bathtub or in a similar situation by throwing a powered-on
electric appliance such a toaster in the water. I don't believe this
would ordinarily electrocute the person in the bathtub; will it?

~Hasan Fakhruddin
Instructor of Physics
The Indiana Academy for Science, Mathematics, and Humanities
Ball State University
Muncie, IN 47306
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