Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

Re: Flashlight

On Mon, 30 Jul 2001, Ludwik Kowalski wrote:

As a pedagogical exercise I plan to create several short essays on basic ideas
of electricity and magnetism. The draft of the first item is on my web site at:

http://alpha.montclair.edu/~kowalskiL/electr/flash.html

The classic diagram of high and low water tanks unintentionally teaches
some misconceptions. Should we try to improve it? Or will improvements
simply make it seem less crude and more trustworthy (so any remaining
misconceptions will be accepted with even less question?)

Below is a diagram which greatly helped me to attain an intuitive
understanding of simple circuits. Rather than using one full container
and one "dry" container, use a pair of containers. This eliminates the
unintentional lesson about empty pipes, and drives home the fact that
conductors always contain charge. It also shows that potential difference
is directly related to the amount of charge imbalance: the pump and not
the pipe's geometery creates the differing water levels. It also stresses
potential DIFFERENCE: for every lowering of the water level in one
side, the level rises in the other side. Turn off the pump, and the
potential difference decays away. But fill both sides with equal extra
water (similar to giving your entire flashlight a net charge), and no
water flows.

|| || || ||
|| || || ||
|| || ||~~~~~~~~~~||
|| || || ||
|| || || ||
||~~~~~~~~~|| || ||
|| || _ || ||
|| ||_______/ \________|| ||
|| _________\_/__________ ||
|| || --> pump --> || ||
|| || || ||
|| ||______ ______|| ||
|| ________======________ ||
|| || <--- <--- || ||
|| || return pipe || ||
=========== ============


You can point out that the "pump" in a dry cell will automatically stall
whenever the difference in "pressure" is such that the water levels differ
by a certain distance. Connect the "return pipe", and the pump will run
just enough to maintain the water level difference.

You can even point out that the currents would be invisible. The water is
visible, but if it has no dirt or bubbles, the motion of the water cannot
be seen. The electron-stuff which flows within metals is completely
visible, yet it behaves like water in that it's flow cannot be seen. I
like to point out that a dense population of electrons will act like a
good reflector of light, so we should expect the electron sea that flows
through metal wires to be a "silvery fluid."


((((((((((((((((((((( ( ( ( ( (O) ) ) ) ) )))))))))))))))))))))
William J. Beaty SCIENCE HOBBYIST website
billb@eskimo.com http://www.amasci.com
EE/programmer/sci-exhibits science projects, tesla, weird science
Seattle, WA 206-789-0775 freenrg-L taoshum-L vortex-L webhead-L