I was reading electromagnetic induction and came across EMF.Now in my text book as the theory has been developed ,they have many a times talked about direction of EMF.

But they have not clearly defined it.When i searched Google,I got this-

Electromotive force, also called emf( measured in volts), is the voltage developed by any source of electrical energy such as a battery or dynamo.[2]

The word "force" in this case is not used to mean mechanical force, measured in newtons, but a potential, or energy per unit of charge, measured in volts.

In electromagnetic induction, emf can be defined around a closed loop as the electromagnetic work that would be transferred to a unit of charge if it travels once around that loop

So if it is actually work done,how come it has a direction?


The definition of EMF involves a line integral. All line integrals require a specified start point, end point, and path. You can assign a direction to the path, so you can loosely connect "direction" and "EMF."

I say loosely because EMF itself does not have a direction, but you have to choose a direction in order to get a value for EMF.

Once you're comfortable with line integrals, you can convince yourself that reversing the path direction amounts to changing the sign of the path integral. It's because of this that one can say "EMF upward is positive" and equivalently "EMF downward is negative." The directions here refer to the direction of the path taken.

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  • $\begingroup$ Ok I have read the wiki articles and took me 2 days to actually get the feel of it...But I still have two questions- $\endgroup$ – soumyadeep Sep 21 '14 at 10:35
  • $\begingroup$ 1.How come there are different definitions for a same physical quantity? $\endgroup$ – soumyadeep Sep 21 '14 at 10:36
  • $\begingroup$ 2.Here for the induced EMF, there is a closed integral involved.So what do we do if we want to calculate it between two different points??And maaany more questions are coming by... $\endgroup$ – soumyadeep Sep 21 '14 at 10:38
  • $\begingroup$ You should ask those as a separate Physics.SE question. $\endgroup$ – BMS Sep 21 '14 at 15:54

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