Question

While we derive emf of a cell, when no current is drawn from the cell shouldnt the potential difference be 0 ? How is it equal to emf of th cell? How can we equate IR= E-Ir?

Answer 1

Emf is basically the electromotive force.
It is defined as the word done on a unit charge to travel through it. So, Emf is always there if the battery is connected in circuit of not!
IR = E - Ir, it is the Kirchoff voltage law that we write in a closed circuit.
IR, E , Ir all are voltages and there sum should be zero!