[Prev][Next][Index][Thread]
RE: FAQ questions...
>Message-ID: <199607090925.DAA03262-at-poodle.pupman-dot-com>
>Date: Tue, 9 Jul 1996 03:25:05 -0600
>From chip-at-poodle.pupman-dot-comMon Jul 8 22:54:39 1996
>Date: Mon, 8 Jul 1996 22:54:17 -0600 (MDT)
>From: Chip Atkinson <chip-at-poodle.pupman-dot-com>
>To: Tesla List <tesla-at-poodle.pupman-dot-com>
>Subject: FAQ questions...
>
>Greetings,
>
>I am starting to work on the safety FAQ, but naturally am having some
>questions. (I'd like to be as accurate as possible)
>
>1) Is it true that it takes 10 Joules of electricity to kill someone?
> (If not, how much is it?)
People drown in the ocean, but it only takes a cup of water in the
lungs to drown a person.
10 watt*seconds? Sure, that'll do it. But it depends on *where* in
the body it goes, and what frequency. 60 Hz is particularly lethal
to the heart. I believe it takes only microamps of current for a
second or so directly into the heart. So people with
under-the-skin heart pacers are a particular risk in high RFI
situations, or electrical shocks of any kind, especially on the
chest or arms.
I have a multi-paged document on this exact question (the
lethalness of electricity, and necessary safety practices) which
was just issued by our Industrial Saftey Officer last month as
mandatory reading for all Operations.... I shall have to mail it
to you when I get back to work in the next couple weeks. Remind
me, please.
>
>2) Is a watt in AC roughly volts*amps? I believe that a watt is VA in
> DC, and if you are dealing with RMS Volts and amps, does that make it
> true for AC?
I presume you're talking about a simple circuit of one AC source
connected to one AC load via two wires.
For this circuit, watts (the actual energy per second taken or used
by the load) equals Volts times Amps time the cosine of the angle
between them. {Angles are often symbolized bu the Greek letter
theta which looks like a right-tilted zero with a horizontal line
through the middle.)
The Volt*amp figure in an AC circuit represents the energy per
second which is sloshing back and forth between the load and the
source. The volts are real, the amps are real (and heat bad
connectors!), it is just that they aren't happening or doing the
same thing at the same instant in time. On parts of the cycle
where the votlage and current are the same direction, the source is
giving energy to the load. On the other parts of the cycle where
the voltage and current are the opposite direction, the load is
giving energy back to the source.
The energy per second sloshing around is volts times amps. The
part used by the load is volts times amps times the cosine of the
phase angle theta between them. [So the LOAD gives back the
difference between the volt*amp figure and the
volt*amp*cosine-theta figure.]
A pure inductor has the current lagging the voltage by 90 degrees:
the cosine is zero and there is no net energy used by the coil. A
pure capacitor has the current leading the voltage by 90 degrees:
the cosine is also zero and there is no net energy used by the
capacitor. But the amount of energy **stored** by the inductor or
capacitor can still be huge!!
>
>Thanks for your attention. More questions will follow I'm sure.
>
>Chip
You're welcome. Anytime.
Fred W. Bach , Operations Group | Internet: music-at-triumf.ca
TRIUMF (TRI-University Meson Facility) | Voice: 604-222-1047 loc 6327/7333
4004 WESBROOK MALL, UBC CAMPUS | FAX: 604-222-1074
University of British Columbia, Vancouver, B.C., CANADA V6T 2A3
"Accuracy is important. Details can mean the difference between life & death."
These are my opinions, which should ONLY make you read, think, and question.
They do NOT necessarily reflect the views of my employer or fellow workers.