MadSci Network: Physics
Query:

Re: How could a 9 volt battery give a painful shock?

Date: Mon Feb 9 08:34:38 1998
Posted By: William J Bray, RESEARCH AND DEVELOPMENT
Area of science: Physics
ID: 886590973.Ph
Message:

There are two things to consider, concerning what will give an unpleasent 
or even painful, posibly deadly electric shock; namely, voltage and 
current.  Nicholi Tesla showed that several hundred thousand volts could 
run through a human being safely if at high frequency (alternating current) 
or very low current (low amperage, in the micro ampere range).  Tesla coils 
and Van De Graff generators, which generate very high voltage in the 
hundred thousand volt range but at very low amperage are excellent at 
demonstrating this.  In fact, some scinece exhibits such as the Franklin 
Institute in Philadelphia have a great deal of fun with the crowds using a 
Van De Graff generator which can throw an electric arc several feet to your 
hand without hurting you.  And if fifty people are holding hands they all 
feel the jolt.  A Van De Graff generator is very easy to build from home 
junk parts and the design can be had by searching around any high school or 
local library.  Begin by looking through science projects books in physics. 
 This is an excellent science project, I would know because my brother and 
I built one when we were kids (they really freak cats out because it makes 
their hair stand strait up from several yards away).  A Van De Graff 
generator sort of looks like a UFO on a pedastool.  In the dark, the static 
which coats the surface (which actually qualifies as a plasma) glows and 
discharges into the air in an eery way.  Tesla coils, on the other hand, 
are a bit more involved to build safely and I'd wait a few years on that 
one.

As far as amperage goes, I believe a standard 9 volt battery has a current 
output of about a hundred milliamperes - which at 9 volts just seems to hit 
the threshold of pain, safely (you ever heard of tongue testing a 
battery?).  A car battery is only 3 more volts, at 12 volts, but has an 
output of several amps and can seriously burn through flesh.  I can't think 
of any other common examples of low voltage-high current off the top of my 
head, but the basic principle is that the current, measured in amperes, 
which indicates the amount of electrons flowing, is what actually 
determines the... severity of the shock, not the voltage. 

Try building the Van De Graff generator, they're a lot of fun to play with. 
 I just searched and found a web site at:
http://www.seorf.ohiou.edu/~xx053/science/vandegraff.html
which gives all the info you need to know and build a VDG.  Havefun.



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