Re: EMF

["John S. Denker" <jsd@MONMOUTH.COM>]

Paolo Cavallo wrote:
> I think that "voltage" refers to the potential difference between two points.

No.  The term "voltage" has never been restricted to potentials.
There are lots of non-potential voltages in the world.
This was discussed at length a while back.
  http://mailgate.nau.edu/cgi-bin/wa?S2=phys-l&s=non-potential
(46 matches)

> If you consider a symmetric ring in a uniform B field changing with time, you
> have an induced EMF on the ring.

You also have an induced voltage (or voltage drop)
around the ring.

> Where are the two points between which there
> is a voltage?

You can't speak of a unique voltage, or a unique EMF,
or anything else as being associated with two points
in this particular non-potential situation.  There
are lots of non-unique ways of measuring a voltage
in such a situation.

In the case of a split ring (C-shaped ring), all the
voltage will be collected at one place, and then
there will be a conventional way to measure it.
The voltage that is provided to the sockets on
the wall of your classroom is of this kind.  So
don't tell me it doesn't exist.

> you must speak of EMF

I must?  Says who?  Why?

I object to the term as being an archaic misnomer.

> and you cannot speak of voltage.

Why not?  I do it all the time.
So do my colleagues.

It's called an induced voltage.
You can call it a non-potential voltage if extra
emphasis is needed.