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Sick of ridiculous KVL infighting
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Naej:
In case someone wants to learn the difference between voltage and potential difference, and why:
https://physics.princeton.edu//~mcdonald/examples/lewin.pdf
https://physics.princeton.edu//~mcdonald/examples/volt.pdf
https://physics.princeton.edu//~mcdonald/examples/voltage.pdf

Have fun.
emece67:
.
RoGeorge:
That integral form is not the definition of voltage.  That's a formula, an equality where V = V/m * m, so V = V after m simplifies away.  It defines V in terms of V, not nice.


I'll take as correct the definition it was given in the primary school, and was used since the early notions of electricity, in terms of energy (work) and charge.  If we imagine we have to drag (as in move, or transport) a charge between to points in space, from A to B, then we define:

Voltage is the work required to move an unit of electric charge between two points A and B.

\[V_{AB} = W/q\]
Where:
- \$W\$ is the mechanical work, the energy involved in moving the unit of charge, energy measured in Joules
- \$q\$ is the electric charge, measured in Coulombs.
bdunham7:

--- Quote from: emece67 on January 15, 2022, 01:43:08 am ---As long as some say that the «voltage» between points A and B is ΦB−ΦA (being Φ the electric scalar potential) and some others say that it is −∫BAE⃗ ⋅dl⃗ , there cannot be any agreement

--- End quote ---


A very succinct statement of what I tried to say much earlier.  Unfortunately, the 'KVLers' apparently didn't understand it either.  However, a few issues with your conclusions...


--- Quote ---
* the second is easier to measure (just ensure there's no varying B field inside the probe wires), but it is path dependent
--- End quote ---

Actually in these cases there is a varying B-field inside the probe wires, just not between the probe wires and the ring.  What the voltmeter ends up seeing is the EMF around the whole outer loop minus whatever voltage drop there is due to resistance in that outer loop.  The fact that this value is the same as what you would expect across the inner resistor is just math.


--- Quote ---Apparently IEC thinks that the "voltage" is that of the 2nd definition, and normal voltmeters, including the 121GW (incidentally, what about a firmware update allowing the user to select the desired voltage definition to use?), do measure according to such definition, so I will continue (it was what they taught me when young) using such definition of voltage. Thus, I will see systems where 2 voltmeters connected to the same points throw different measures, shit happens.

--- End quote ---

Actually, in any reasonable setup where the body of the meter is not placed in ridiculous places, a voltmeter like the 121GW will display a value very close to the ΦB−ΦA 'scalar potential' or 'KVL volts' (my tonge-in-cheek term for it from the other discussion) that is present directly across it's input jacks.  If you do place the meter in some place with a significant curled E-field going through and around the meter, you will likely simply get unpredictably erroneous readings due to the complex internal circuitry of the meter.  The 'path dependence' is all about the test leads, which are just wires that form another circuit.  This might seem like nitpicking, but I think it is not.  Special firmware will obviously not allow you to magically read KVL volts, but it might be possible to come up with a probe set that does.[/list]
bdunham7:

--- Quote from: RoGeorge on January 15, 2022, 02:23:52 am ---Voltage is the work required to move an unit of electric charge between two points A and B.

--- End quote ---

That is one definition and for many things, likely the most sensible.  However, it is not the only reasonable or possible definition.
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