Consider an ideal emf (zero internal resistance) connected across a
resistance, After a transient period of time, an electrostatic charge
distribution appears which produces potential differences between
space-point pairs.
The potential difference across the resistor is equal to the work done by
the electrostatic field on each coulomb that traverses the resistor and is
thermally dissipated. This is also numerically equal to the "emf" - which
is defined as the work done by the (ideal) emf in lifting a coulomb up that
same potenial difference as it flows through the emf device (against the
electrostatic field).
Note that we use the word "emf" in two ways - the name of the energy
conversion device, and a measure of the energy conversion capability of that
device (in Joules per Coulomb).
The emf (both the device and its "measure") exist and operate even during
the transient period; the potential differences (in space and across circuit
elements) build up in time as the transient effect settles down.
Bob Sciamanda (W3NLV)
Physics, Edinboro Univ of PA (em)
trebor@velocity.net
www.velocity.net/~trebor