If EMF and the potential difference have a unit of volts, why are they different from each other?

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    \$\begingroup\$ This question is essentially asking for tuition on basic electronics, page 1 stuff. It's a Q&A site, rather than discussion forum, and can't be a personal tutorial service, which is effectively what you're asking for. VTC for those reasons. You'll find plenty of detailed and free documentation on this available on the internet for you to research and learn from. Hope you can see how the site works but refer to other high-voted questions for examples of what's well-regarded here. Thanks. \$\endgroup\$
    – TonyM
    Commented Aug 21, 2022 at 20:22
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    \$\begingroup\$ Do you have an example? Normally I would consider them to be almost synonyms. The only thing is that I tend to use EMF when I want to emphasize that the potential difference was created by induction. \$\endgroup\$
    – user57037
    Commented Aug 21, 2022 at 20:23
  • \$\begingroup\$ You can have an EMF without any potential difference between any two points. For example a shorted battery or a single shorted turn on a transformer. \$\endgroup\$ Commented Aug 21, 2022 at 20:38
  • \$\begingroup\$ @KevinWhite EMF with zero potential difference is not possible or not conceptually meaningful as far as I can see. In both of the examples you give, the potential difference is not and cannot be zero. If the potential difference between two points is zero, then either the current is zero, or the two points are connected by a super-conductor. Maybe there is something that could be done with hall effect or something to create zero potential in the presence of current flow. I don't know. But not in your examples. \$\endgroup\$
    – user57037
    Commented Aug 21, 2022 at 20:50
  • \$\begingroup\$ @mkeith Superconducting solenoids work just fine as transformer windings, though. So zero impedance is not a problem for getting charge moving, and for adding energy to a solenoid, or removing energy from it. \$\endgroup\$ Commented Aug 22, 2022 at 0:03

2 Answers 2


electromotive force,
abbreviation E or emf, energy per unit electric charge that is imparted by an energy source, such as an electric generator or a battery. Britannica

potential difference
the difference in potential between two points that represents the work involved or the energy released in the transfer of a unit quantity of electricity from one point to the other. Merriam-Webster

I suggest that electromotive source suggests a source of power whereas potential difference, while it could measure an electromotive force, can be measured on a non-source element of a circuit such as a resistor.

Quick and easy:

  • EMF is what batteries, generators and power supplies give.
  • PD is what your voltmeter measures.
  • \$\begingroup\$ Electricity is not a potential field when changing magnetic fields are involved, which is probably why people don't talk about PD. Though everyone I know just talks about "voltage" in context. \$\endgroup\$ Commented Aug 22, 2022 at 17:23

They are descriptions of somewhat different phenomena. EMF is more specific than voltage.

'EMF' is generally used to describe a source of voltage (energy or power) -- for example a coil moving in a magnetic field generates an EMF.

To measure the phenomenon generated, the result is described in volts -- e.g. a "voltmeter" could measure the EMF generated by the above coil.

If you have a circuit with a battery and some resistors, the battery can be described as generating an EMF of 1.5 V, while the same phenomenon across the resistors is described as a voltage.

EMF is also used to describe the (voltage) generated by a thermocouple -- or even the unwanted phenomenon generated by dissimilar metal junctions. Commonly batteries (and power supplies, solar cells etc.) are just described as voltage sources. This is not incorrect, just slightly less specific.


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