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Re: current density ????



Brian

Your answer to my simple question was excellent in all respects. Why
don't you spend
a few minutes polishing it up and then submit it to The Physics Teacher
for publication.
It is certainly worth sharing with others and could be expanded to
include the genesis of other similar terms that we use in physics.

When you do, send it with a short note to the editor, Clif Swarz, telling
him that I suggest that he schedule it for early publication.

Herb

On Sat, 01 May 1999 02:28:04 -0500 brian whatcott <inet@INTELLISYS.NET>
writes:
At 11:19 4/30/99 -0400, Herb wrote:

What do you mean by "current density?" Current refers to the number
of
electrons that pass a given point in a given amount of time.
But CURRENT DENSITY
?????

Herb Gottlieb from New York City
(Where our population density is greatest in the inner city)


I find it helpful (like Herb evidently does) to think in terms
of science keywords.
So density starts out as a particular ratio:
e.g the ratio of mass per unit volume

The idea is generalized to
energy density - the energy per unit volume
charge density - the charge per unit volume
and (incorrectly) to
current density - the current per unit volume
when really, the current per unit cross-sectional area, is meant.

But this usage is by now enshrined and won't be shamed
from existance.

Compare the suffix "DENSITY" with the prefix "SPECIFIC".

Specific volume is volume per unit mass, for instance.
Then there's specific activity (activity per unit
mass of pure radioisotope), specific heat capacity
(heat capacity per unit mass), specific resistance (or resistivity)
and even specific impulse: impulse per unit fuel mass,
derived in a slightly tortured way from force or thrust per
unit fuel mass flow rate.
This too enshrined in custom as a 'time' by dividing units of
force by units of mass - not always wise.

Brian

brian whatcott <inet@intellisys.net>
Altus OK