Re: AC electricity

[Bob Sciamanda <trebor@VELOCITY.NET>]

Since the charge carriers are driven by the local E field,  positive
carriers will go in E's direction and negative carriers will go in the
opposite direction. Both constitute a current in E's direction.

Now if you added some non-electrical, selective force . . . hmmm.

In a hall effect device, a magnetic force contributes to a perpendicular
current!
In a generator armature, a magnetic force contributes to a forward
current.

In a transistor, a diffusion current flows against the field (across a
reverse-biased junction) from the base to the collector.

All emf's which are supporting a current are using some non-electric
effect to move carriers against the local electric field inside the emf. .
. but this is not what you ask for - there is no simultaneous current in
the direction of the E field here.

Bob

Bob Sciamanda (W3NLV)
Physics, Edinboro Univ of PA (em)
trebor@velocity.net
http://www.velocity.net/~trebor

----- Original Message -----
From: "Ludwik Kowalski" <KowalskiL@MAIL.MONTCLAIR.EDU>
To: <PHYS-L@lists.nau.edu>
Sent: Wednesday, January 17, 2001 04:03 PM
Subject: Re: AC electricity


> 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