Re: Meauring Volts?

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

Edmiston, Mike wrote:

> this is not something to lose sleep over,

Right.

> agree with Herb that we ought to keep working at getting students to
> speak and write correctly.

Agreed in principle, but what's the problem here?

If I see a sign that says "5000 cars in stock"
I might say "wow, that's a lot of cars".
If I see a sign that says "5000 volts"
I might say "wow, that's a lot of volts".

I'm not at all convinced that usage is wrong.
If it's wrong, it's not very wrong.
I object to terminology when it leads to
misunderstanding, and I vote "volts" as
not guilty.

I think I prefer "voltage", but not enough to
spend even a femtosecond of class time on it.

> Early on, I try
> to say electric potential difference when I lecture or work with
> students.  After a little while I switch over to voltage, but I still
> occasionally throw in EPD to remind them and/or keep them on their
> toes.
Now that I object to!
Pleeeeease don't give them the impression that
EPD corresponds to voltage, let alone defines
voltage.  There are lots of non-potential
voltages in the world.

> Alas, it does not seem to be working.  They neither get the electric
> potential difference nor the voltage (and probably wouldn't get oomph
> either); they just get the volts.

Can you be more specific about what the problem is?
What's an example of a physics problem they ought
to be able to do but can't?

> Along these same lines, I worry that our tendency to abbreviate things
> with one letter also leads to confusion.  If we have an electric
> potential difference of 5 volts, many scientists will write this as V
> = 5V.

> Aside from the fact that some students view this as algebraic
> nonsense,

Confirming their suspicion that the physics
professors are demented....

Electrical engineers often write E for the
voltage, as in E=IR.  I don't recommend that,
because then you're painted into a corner
when it comes time to discuss the electric
field.  Using Phi for the potential (IF your
voltage is a potential) seems safe and easy.

> it also has the problem that it ought to be delta-V.

Well, maybe it ought and maybe it oughtn't.
IF (big if!) you have EPDs, then you can
choose a gauge and have an EP, which is
measured in plain old volts.

If you have a non-potential voltage, you will
need more than a "delta" to disambiguate things.