[PmbPhy]

I forgot to mention that a rotating magnet can generate a static electric field.

[vhfpmr]

I'm still quite lost, I'm not sure which bits PmbPhy is retracting and which not (if any).

There's a difference in potential between two points in a static electric field but such a field cannot produce a steady current in a resistor whereas an EMF can.

This seems to me a bit like arguing that there is a difference, in kind, between the metre used to measure the position of a point in empty space, and the metre used to measure the height of a reservoir that can generate power in a hydro plant. Distance is distance.

FWIW, and digressing a bit from electrostatic fields, my usage of the two terms as a radio engineer is that EMF is conventionally the source voltage of a Thevenin source, and the PD is the terminal voltage. My point is that these are both voltages, with no difference in kind, and the terms merely distinguish between two different locations in the equivalent circuit. (Both would be the same magnitude of course when no current flows, as with an electrostatic field.)

Re: a charged particle, if I charged a speck of dust using a van der graaf, and then placed it between two parallel plates connected to a battery, would it not be attracted to one of the plates?

[PmbPhy]

This seems to me a bit like arguing that there is a difference, in kind, between the metre used to measure the position of a point in empty space, and the metre used to measure the height of a reservoir that can generate power in a hydro plant. Distance is distance.

Your analogy is flawed. In almost no difference in the examples you just gave.  To specify a point in space you need a point of reference and a displacement vector from that reference point to the point you wish to specify. The reference point is arbitrary. The magnitude of the displacement vector is the distance. The displacement vector is called the position vector. The height of a reservoir is the magnitude of the distance from the reference point to the height of the reservoir. The reference point is still arbitrary. Its usually chosen to be the point of lowest place that the water can go to. However you can also dig a well in which the water can fall further and then use the bottom of the well as the reference point.

While distance is distance, EMF is physically different than difference in potential. That's because they  are defined differently. In fact its impossible to have a difference in electric potential in the absence of an electric field but its quite possible to generate an EMF without an electric field. In fact a dynamo works by moving a conductor through a magnetic field which does work on the charged particles in the conductor which can then be used to generate energy in a circuit. But there's no need for an electric field in this case and therefore no electric potential.

FWIW, and digressing a bit from electrostatic fields, my usage of the two terms as a radio engineer

I don't see what being a radio engineer has to do with anything.

The definition of difference in potential and EMF as defined in physics are as follows:

An electric potential is the amount of work needed to move a unit positive charge from a reference point to a specific point inside the field without producing any acceleration.

An electromagnetic force (EMF) is defined as that which can produce energy to generate an electric current or  in another context a line integral containing a magnetic term.

There is, in fact, no requirement for an electric field or a battery to even be present to generate an EMF.

See the definition of EMF in any one of the classic texts in EM such as Jackson. Other great texts on the subject are Zangwill or Grtiffiths. All too easily people confuse the terms merely because they have the same units.

[PmbPhy]

I posted the following link above: https://en.wikipedia.org/wiki/Electromotive_force#Electromotive_force_and_voltage_difference

I should point out that there are misleading comments in that page. E.g. it says

The electric charge that has been separated creates an electric potential difference that can be measured with a voltmeter between the terminals of the device.

In the region surrounding a charged object there is an electric field and as such differences in potentials. But you cannot measure those differences with a volt meter.

[vhfpmr]

In fact a dynamo works by moving a conductor through a magnetic field which does work on the charged particles in the conductor which can then be used to generate energy in a circuit. But there's no need for an electric field in this case and therefore no electric potential.

If I move a wire through a magnetic field there will be a voltage difference generated between the ends. If I were to place a speck of charged dust nearby, would it not be attracted to one end of the wire because there is now an electric field surrounding the wire?

I don't see what being a radio engineer has to do with anything.

The relevance is that radio engineers all understand the terms EMF and PD in the context of a Thevenin source, as defined above.

An electromagnetic force (EMF) is defined as that which can produce energy to generate an electric current

Ok, so how is that different from PD? Using my definitions of EMF and PD, I could construct a Thevenin source with an infinite resistance, such that the EMF can deliver energy but the PD cannot, would that not then satisfy your distinction between the two terms?

[PmbPhy]

If I move a wire through a magnetic field there will be a voltage difference generated between the ends. If I were to place a speck of charged dust nearby, would it not be attracted to one end of the wire because there is now an electric field surrounding the wire

That applies only to a static situation and is indeed a difference in potential. But its not am EMF because (1) it does not conform to the definition of EMF and (2) it cannot supply

I don't see what being a radio engineer has to do with anything.

The relevance is that radio engineers all understand the terms EMF and PD in the context of a Thevenin source, as defined above.
[/quote]
Irrelevant since your responses suggest you are confusing an EMF with a legitimate PD.

I will not continue with this since there are numerous authoritative sources available online with clealy explain the differences. If you refuse to look them up then it seems to imply that you don't want to learn but would rather argue.  E.g. The line integral defining a motional EMF is the integral of vxB.
You're confusing the induced electric field for an open circuit with an EMF?

Since there's ample information online which I already pointed out and you chose to ignore. i.e.  Jackson, Zangwill and Grtiffiths I see no reason to repeat myself.

[evan_au]

How about this scenario:
- Take a 1.5V battery, which produces a 1.5V EMF
- Connect it to a parallel-plate capacitor, which now has a 1.5V Potential Difference between the plates
       - There is a static electromagnetic field between the two plates, with the field direction being pretty much a straight line between the plates
       - There is a slight fringing field extending beyond the edge of the plates, with the field direction bulging out and curving back in to the other plate
       - You can manipulate the electromagnetic field of the capacitor in various ways, eg:
       - You can increase or decrease the separation of the plates; early experiments with electrostatics mounted the parallel plates on a screw thread so you could increase or decrease the separation
       - You could change the area of the plates; analogue radios had a mechanical method of changing the amount of overlapping area of the plates
       - You could insert materials with different e values

What happens to the voltage depends whether you have the battery still connected or not; the battery will tend to maintain a constant 1.5V across its terminals, and so a current will flow to keep the voltage across the capacitor plates constant while it is connected.

However, if you disconnect the battery before manipulating the capacitor, the charge on the plates is constant, and the voltage on the plates will vary as you change the physical structure of the capacitor.

You can image the electric field strength by using commercial mathematical simulation packages.
- Or you can use a very high impedance voltmeter, with higher impedance that air leakage
- Or, in principle, you could use a device that counts the individual electrons flowing from the more positive terminal to the more negative terminal. This could use totally insulated probes and draw no current from the EMF or PD.

With an old-fashioned "pile" battery, consisting of alternating copper and zinc disks of equal size, the internal EMF may cancel the straight-line electric field between the top and bottom plate.

But if you make the top and bottom plates bigger - in fact, like a capacitor, you will have a static electric field between these plates, plus a fringing field.