Re: Series, Parallel, and Resistivity Equations

[Bernard Cleyet <anngeorg@PACBELL.NET>]

interleaved below:

David Bowman wrote:

> Regarding the analogies mentioned by John Cockman:
>
> > There are two analogies that I like to use when I introduce this subject:
> >
> > Voltage is like a water tower high above the ground -- the water is current,

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> .
>
> The water-in-a-pipe analogy is *not* particularly accurate in terms
> of modeling the behavior of electric current in an ohmic resistive
> medium.  The problem is not with the resistance being proportional to
> the path length, but with it being inversely proportional to the
> cross section area of the flowing current.
>
> In its usual form the flow of a liquid through a pipes does *not*
> have the same mathematical description of for the fluid flow as that
> of DC electric currents in electrical conductors (unless the pipe
> happens to be stuffed with a very fine-pore porous wadding).  The

And you think the students know this?   If they did, then there would be no need
to discuss the factors that determine electrical resistance.

Is this a case where an incomplete analogy is heuristic?

bc


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