Question

basic concept of emf and pd....how to distinguish it in circuit...

Answer 1

What is the difference between electromotive force and potential difference?

I=V/R versus V=I*R

If the voltage is the cause (of a current flowing through a resistor, say), it is an electromotive force. If the voltage is the effect (of a current flowing through a resistor, say), it is a potential difference.

Consider a charge in space. Now, consider any two points (obviously not on the same spherical plane!) and there exists a potential difference between those two points. If u connect a conducting wire between those two points, no current flows.
Now, consider a battery, a potential difference, known as emf (electro-motive force) exists between its two terminals..... Connect a conductor between them, and current flows. Thus emf refers to the ability of a potential difference to actually force electrons to flow in a closed circuit.!
...though you are not satisfied visit Google ..WIKIPEDIA

Answer 2

$<b><i><u>$

generally when a source is supplying power EMF>PD, where as when it is getting power from outside thenEMF<PD. The difference in potentials between two terminals of a battery in a open circuit is EMF .The difference in potentials between any two points in a closed circuit is potential difference .