[Beowulf] Re: A start in Parallel Programming?

Robert G. Brown rgb at phy.duke.edu
Wed Mar 14 17:06:57 EDT 2007


On Wed, 14 Mar 2007, Peter St. John wrote:

> What General Physics I teaches about wiring would not be adequate to work as
> an electrician in home construction, but it's adequate to do the bench
> experiments that illustrate the concepts. There are many purposes under the
> sun.

I'd take issue with this.  It is ALMOST adequate to work on home
electricity, at least if you have a good teacher.  It is certainly
adequate to cover the basic physics that underlies e.g. becoming a
journeyman electrician (I know as my brother-in-law is one, and I went
over his studies with him on several occasions).  In fact it is a fairly
precise match -- you cover JUST enough about how electricity works to be
able to become an electrician.

So yeah, it doesn't teach you the right gauge of wire to use for a given
current and run length, it doesn't teach you what local electrical codes
are, it doesn't teach you how to wire for inductive loads, and it
CERTAINLY doesn't teach you how to work with 16 KV transformers that
will kill you dead if you do not follow certain solemn rituals.  It does
teach you all you need to understand why the right gauge of the wire is
right (Ohm's law, resistivity/conductivity, heat production under
various expected loads, voltage drop across the wire as opposed to the
load).  It does teach you, point by point, what you need to know about
WHY the electrical codes are what they are, and even enough to be able
to figure out when they can be bent a bit and when they aren't really
adequate.  It doesn't teach you all about large transformers or high
voltage, but it does teach you Faraday's law and RLC circuit analysis,
it does teach you that high voltage is dangerous -- and why we use it
anyway in order to move electricity from place to place with minimal
Ohmic loss.

Indeed, the only thing it is missing is the right problems being
assigned, and a bit of hands on experience, both of which COULD be done
in lab (hmmm, I'll have to speak with my lab TA about this, as I'm
teaching intro E&M at this very moment:-).  Since I do my own wiring
when it is reasonable to do so, I actually do tell them quite a bit
about real world wiring -- what hot, neutral and ground are, why
inductive loads (or loads in general with PF < 1) are different from
resistive loads, why 12 Gauge wire is generally safer than 14 Gauge wire
in nearly all cases in home wiring (and required by code for longer
runs), why 10 would be better still except for the expense, the fact
that it is a total PITA to bend and pull, and the fact that most
receptacles can't easily or safely manage it.  I even try to tell them
why one puts a lamp switch on the HOT line going into the lamp, not the
NEUTRAL line coming out of it, and why Ground Fault Breakers Are Good.

When I'm done, they might not be ready to "just wire things", but they
are definitely to where they should be able to buy an over the counter
book at Home Depot and wire anything they like, subject more to their
general competence with tools and ability to follow directions than
their inability to understand how Mr.  Electricity works...

    rgb

-- 
Robert G. Brown	                       http://www.phy.duke.edu/~rgb/
Duke University Dept. of Physics, Box 90305
Durham, N.C. 27708-0305
Phone: 1-919-660-2567  Fax: 919-660-2525     email:rgb at phy.duke.edu


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