# Is EMF a force? [duplicate]

I had a confusion. EMF stands for electromotive force. Is it a force? I have a short question and I can't elaborate more but this site is not allowing me to post so I am writing.

• Hello! Is there anything particular that you don't understand about the Wikipedia article? Especially "The word 'force' in this case is not used to mean forces of interaction between bodies" – Jonas Jun 11 at 18:42
• I second Jonas comment. I suggest you read the Wikipedia article and then, if you still don't understand, come back. – Bob D Jun 11 at 19:24
• It is a very old name from about 1830, before electricity and magnetism were well understood. Today we would say it is potential difference or voltage. This is what makes a current flow in a conductor. Since it makes charges move, it was natural to think in terms of force. "Electromotive" force because it made electricity move. – mmesser314 Jun 11 at 20:26
• Does this answer your question? What is Electromotive force (EMF)? How is it related to potential difference? – Sebastiano Jun 11 at 21:41

It is not a force - it provides an electrical potential (voltage). Specifically, it has dimensions of potential energy divided by charge.

One usually thinks of an EMF in terms of something like a battery that has a voltage between its terminals. The rate of change of a spatially varying voltage is the electric field. The actual force on a particle is its charge times the electric field.

• It provides voltage in some cases, but that is not its defining characteristic. For example, induced EMF in a circle may not produce any voltage if the field has line of cylindrical symmetry that is also line of symmetry of the circle. – Ján Lalinský Jun 11 at 22:11
• This answer would be more accurate if "It is not a force" were changed to "It is not a mechanical force". In thermodynamics, all conjugate work pairs are treated as generalized forces and generalized displacements whose product has units of energy. Voltage is one such generalized force (charge is its conjugate generalized displacement). – Chemomechanics Jun 12 at 0:41

Induced EMF is integral of induced electric field over some path. In the simplest case, it is the product of induced electric field and some length. This quantity can be understood as work of induced field per unit charge when it gets transported along specific path. Its unit is Joule per Coulomb which is Volt.

It is a "force" not in the sense of mechanics, but in the sense of "driving force" behind electric current, because it can drive electric current in a circuit. In the simplest case like a circuit made of wire in changing magnetic field, current in the circuit is approximately proportional to induced EMF in the whole circuit.

Emf is not a force in the strict sense. Nor is it an electric potential, though it has the same dimensions. It is work per unit charge done in moving charge around a circuit.

It is commonly confused with potential because it is often the potential difference that is doing the work, so they are often equal. For example, the potential difference across the resistor is $$-IR$$ by Ohm's law, and this is also equal to the emf applied to the circuit by the resistor. However, it is also possible to apply an emf to a circuit that is not associated with a potential, for example by induction.

The relationship between emf and potential is EXACTLY the same as the relationship between work and potential energy. Emf is work per unit charge, potential is potential energy per unit charge. Work done on a system by a conservative force is associated with a drop in potential energy, but you can also do work on a system by nonconservative forces.

(As @Chemomechanics points out, emf can be considered a "generalized force" from a thermodynamics point of view, but otherwise the term "force" in "electromotive force" is a misnomer.)