Re: AC electricity

[William Beaty <billb@ESKIMO.COM>]

On Wed, 17 Jan 2001, Tim O'Donnell wrote:

> quantities, but I still don't think I have a basic
> understanding on "how" it really works.

Yeah, that's something that's never specifically taught in books.
They'll just tell you that, because the voltage reverses AND the current
reverses, the energy still flows in the same direction, since negatvie
times negative is still positive (volts times amps).

Here's an analogy:

   - scrub the floor with a brush.  The floor gets hot.  You've
     done work, and some mechanical energy has flowed out of your muscles
     and into the brush, where it gets converted into frictional heat.

   - instead place the brush on the end of a long rod.

   - now scrub the floor by pushing the OTHER end of the rod back and
     forth.  The brush scrubs the floor, and the floor gets hot.

   - mechanical energy has flowed ALONG THE ROD on its way from your
     muscles to the floor.

   - PULL on the rod, and the brush heats the floor frictionally.  Or
     PUSH on the rod, and the same thing happens.  It doesn't matter
     which direction you move the rod; in both cases the energy flows in
     just one direction: from muscles to floor.

In a circuit, the column of electrons inside a wire functions as the
"long rod."

When a generator is used to light up a light bulb, it doesn't matter which
way the electrons flow (or whether they vibrate instead of being DC.)  The
energy still moves in one direction from generator to bulb.  To make the
analogy a bit more complete, replace the rod with a circle of rope which
passes around two pulleys.  When you force one pulley to turn, the other
one turns too.  Attach your scrub-brush to any point on the rope.  When
you turn one of the pulleys, the brush scrubs the floor.  The rope has the
same function as the "loop" of electrons which exists inside an electric
circuit.


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