Re: EMF

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

Shawn Knudsen wrote:
> I think you should stick with "electromotive force" yet explain the
> appropriate concept to your students.  The reason I say this is simply that
> after your students leave your classroom, the rest of the world (barring a
> few on this Phys-L list) will refer to EMF as "electromotive force."

Why is that relevant?  Most people don't refer to EMF
at all.

According to google, voltages outnumber EMFs by 15 to 1.

I thought "EMF" was replaced by "voltage" about the time
"condenser" was replaced by "capacitor" i.e. many many
years ago.

I wouldn't spend more than 2.5 seconds of class-time on
this issue.  Say "EMF is a quaint archaic deprecated term
for voltage" and move on.

Ludwik Kowalski wrote:
...
> On the other hand, voltage usually reefers to what a voltmeter
> is reading. Since voltmeters are never ideal, one may argue,
> then the EMF is not the same thing as voltage.

I don't buy that argument.  I object on principle.

Voltage is _not_ defined to be whatever the voltmeter
reads.  Suppose a voltmeter is broken (open-circuited)
such that it always reads zero.  Attaching such a meter
to nodes A and B doesn't mean the voltage V_AB is zero.

We don't have ideal ways of measuring acreage, yardage, or
tonnage, but those remain perfectly well-defined concepts.
The same goes for voltage.

The voltage that can be measured is not the true voltage.
The word that can be spoken is not the true word....