Emf: Emf is defined as work done per unit charge in taking a positive charge through the complete circuit ( the circuit outside the source (cell) and inside of the source. emf is represented by greek letter ε

If W is the work done when a test charge of q is taken through the complete circuit of a cell with a external resistance or lamp etc. Then emf of the cell is : ε=W/q
For detail watch the video.
If you have any confusion then ask below in the comment box.

READ :  4. Rating of Electrical Appliance and Calculation of Electrical parameters