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Propeller Head Plaza Technical and scientific discussion of amps, cables and other topics. |
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Propeller Head Plaza Technical and scientific discussion of amps, cables and other topics. |
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In Reply to: Correctomundo posted by unclestu on February 23, 2014 at 16:14:29:
Stu,How about your comments on my original posted message.
The more I look the more info I find.
Example.
Understanding Electricity and Circuits:
What the Text Books Don’t Tell You
Ian M. Sefton
School of Physics, The University of Sydney
I.Sefton@physics.usyd.edu.auQuote.
Part 1 IntroductionMost of the standard physics text books that we all know and either love or hate have some serious
deficiencies. My particular beef here is that, by trying to oversimplify some basic physics, those
books introduce or encourage some serious misconceptions and tell stories that are hard to believe.
For this discussion I have chosen the topic of simple circuits as exemplified by a battery and a small
torch globe – can we find a simpler circuit than that? I will use that example to explore some really
important physics that all school-level and most junior university-level texts omit and to confront a
serious misconception that can arise from studying those texts.
There are four main parts to this article. In part 1
I introduce the example and in part 2 we have a
look at the misconception about energy transfer
together with a quick summary of a better model.
In parts 3 and 4 we will examine the basic
physics in more detail and justify the alternative
model by applying the principles to the example
in more detail. For an overview of the problem
and its resolution you need only read parts 1 and 2.Part 2 Demolition of a Myth
2.1 The basic misconception
The core misconception, propagated by many text books, is that moving electrons (or some other
form of current) in the connecting wires carry energy from the battery to the globe. I can give at
least five arguments why that idea is conceptually unsound. You may be able to think of more.
Objection 1 is that that electrons are just too slow to carry the energy fast enough! When the switch
is closed the light globe comes on almost at once. Many text books discuss a model of electrical
conduction in which a “gas” or “sea” or electrons is pushed slowly along a wire by an electric field.
If you know the density of electrons (the number of conduction electrons per volume of wire), the
diameter of the wire and a typical current you can work out how fast the electron sea moves along.
In a typical example of a 1mm copper wire carrying a current of 100 mA the answer turns out to be
about 0.01 mm.s-1 which is much slower than a tortoise. If those electrons were picking up energy
from the battery and then carrying it all the way to the light globe, you would have to wait an
awfully long time to see the globe light up.
Objection 2 looks at AC circuits in which electrons don’t go anywhere much; they just jiggle back
and forth. So they can’t carry energy from one place to another. It would be silly to have a basically
different theory for AC and DC.Please read the rest of the white paper.
http://science.uniserve.edu.au/schoo...002/sefton.pdf
Edits: 02/23/14 02/23/14
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Follow Ups
- RE: Correctomundo - jea48 17:15:14 02/23/14 (0)
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