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:[EMAIL PROTECTED] _______________________________________________ Beowulf mailing list, Beowulf@beowulf.org To change your subscription (digest mode or unsubscribe) visit http://www.beowulf.org/mailman/listinfo/beowulf
