Re: AC electricity

[Ludwik Kowalski <KowalskiL@MAIL.MONTCLAIR.EDU>]

Tim O'Donnell" <odonnt@CELINA.K12.OH.US> wrote:

> I know that AC delivers energy - that is obvious.
> But I still have trouble understanding how this is possible
> since half the time the potential is positive and the other
> have it is negative.  It seems they should cancel out.
> I know and can do the rms (root mean squared - although
> shouldn't it be squared mean root) for figuring out various
> quantities, but I still don't think I have a basic
> understanding on "how" it really works.

Bob Sciamanda replied:

> > How about an AC force which alternately pushes a mass
> > back and forth -like using sandpaper!

Or think about a belt which heats by friction.

The mathematical formula shows that the power,
P=I^2*R, is positive, even when I is negative.

This begs for a gedanken experiment. Suppose two equal
constant currents flow through a wire in opposite directions.
Each current contributes to P but a DC meter (d'Arsenval
galvanometer with a shunt), connected in series with the
wire, would show I=0.

Is it possible to have two equal constant currents flowing
through a wire (or a lamp) in the opposite directions at
the same time? How?
Ludwik Kowalski