Re: [Phys-l] Textbook petpeeves: circuits

[John Denker <jsd@av8n.com>]

Robert Cohen wrote:

>  In the situation being discussed, I
> have used "voltage" to be equivalent to "difference in potential".
> Thus, we could refer to the "voltage" across a resistor or the
> "potential difference" across the resistor but NOT the "voltage
> difference" across the resistor.  Am I wrong in doing so? 

Let's just say that's a new one on me.  It is entirely conventional
to speak of the voltage on a node.  It is a one-terminal concept
(subject to the usual gauge invariance).  Voltage (by definition)
is energy per unit charge, nothing more, nothing less.

>  When we refer
> to the voltage across a resistor, do we really mean the "difference in
> voltage across the resistor"?

I would say yes, definitely.

In the EE community, as my ears hear it:
 -- The term EMF is extinct, except possibly in the idiomatic
  expression "back EMF" associated with a motor.  It is an
  ugly and confusing term, and its passing is unmourned.
 -- The term "electric potential" is nearly extinct.  Firstly,
  it is more verbose than "voltage", and secondly and more
  importantly, not all voltages are potentials.  If you have
  an AC stray field (where "stray" means "violating Kirchhoff's
  'law'") then you will have non-potential voltages.
 -- Yes, we speak of the voltage difference across a resistor,
  but even more commonly this is called the voltage _drop_
  across the resistor;  by way of shorthand this is also called
  simply "the drop" (not "the voltage").
 -- In a circuit where one side of the resistor is grounded,
  then we speak of the voltage "on" the resistor, which is just
  the voltage on the ungrounded terminal ... which of course is
  just equal to the drop across the resistor.