Re: A MISCONCEPTION ITEM

[Rick Tarara <rbtarara@SPRYNET.COM>]

My take on some of these:

----- Original Message -----
From: paul o johnson <pojhome@FLASH.NET>
To: <PHYS-L@LISTS.NAU.EDU>
Sent: Monday, July 26, 1999 3:46 PM
Subject: Re: A MISCONCEPTION ITEM


> Ludwik
>
> You've uncovered my ignorance on the following "Old Misconceptions". I
> copy the ones that elicited a surprised "huh?" from me with my comments
> under each:
>
> 2) The misconception is that absorption by the glass in greenhouses is
> the main factor
>      responsible for higher temperatures inside.
> I always thought it was. What, then, is the main factor?

Convection, or lack thereof is apparently the major factor although I still
use the greenhouse (with an appropriate disclaimer) when trying to explain
the global greenhouse effect.

> 3) Capacitors in series: the equilibrated charges are not equal in the
> dc circuits.
> What are "equilibrated charges"? Surely the charges on adjacent plates
> are equal.

This is Ludwik's child--he'll explain.

>   4) Melting of ice under skating blades is not due to high pressure.
> Not even primarily? Do the metal blades conduct that much heat? Skate
> blades cannot, then, be made of high-strength plastic because they will
> stick to the ice.
>
>   7) Batteries are sources of charge.
> Does charge, then, come from some other macroscopic circuit element?
Batteries are a source of potential difference which can make charges in a
complete circuit 'move'.  The net charge of the circuit is still zero.

>  10) Mechanical friction is not caused by surface roughness or
> "interlocking asperites."
> But surface roughness must be the leading "usual suspect". The
> coefficients are certainly greater for rough surfaces than for smooth
> ones.
Basically, no one _really_  knows exactly how friction works.  I would
guess this refers to an 'electrical force' explanation.  Roughness is still
a factor but not in a 'mechanical way'.  Not sure though.

>  14) The Earth's "N" pole actually resides in the southern hemisphere
> I teach that the "N" geographic pole ain't but the "N" magnetic pole
> sure as hell is.
All this says is that the Earth's North magnetic pole is really a south
magnetic pole by our normal conventions.

>  19) Salt water contains no molecules of NaCl, it contains Na and Cl
> ions
> Not even when the solution is less than saturated?


>  20) Macroscopic light waves do not continue to propagate at c when they
> enter a transparent
>        medium
> Then why does the ratio c/v increase in such a medium?
I question this too.  I had thought through the conventional 'speed of light
is slower in optical media' to really mean that the _effective_ speed is
slower because the light is being absorbed and readmitted and that process
can slow the apparent transversal speed.  I have believed that all E&M
radiation propagates through space at c--period.  In an optical media it
still does, but the 'space' is limited to that between absorptions.

> poj
> Collin County College

Rick

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Richard W. Tarara
Department of Chemistry & Physics
Saint Mary's College
Notre Dame, IN 46556
219-284-4664
rtarara@saintmarys.edu

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