Defining Electromotive Force (\epsilon)

[Petar Mali]

How to define electromotive force?

$$\epsilon=\oint_L\vec{E}\cdot d\vec{l}$$

Can I say electromotive force is work per unit charge which we need to put charge from one place of contoure to the same place?

 

[Dale]

That is the emf due to a magnetic flux. There is also the emf due to a chemical reaction, e.g. in a battery. There is also the emf due to a photovoltaic, or in a thermocouple, etc. There are lots of different kinds of emf, that definition only applies to one kind.