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The electromotive force (EMF) is the maximum potential difference between two electrodes of a galvanic or voltaic cell. 
potentential differnce refer to the differnce which create between two ends of a  the circuit by providing battery or a cell.
it's si unit is volt
                                       formula to find it is p.d=i
                       where i refers to current  
                                                   plz mark it best                                                           
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Potential DifferencePotential is a function of the location, and potential difference between point A and point B is calculated by subtracting the potential of A from potential of B. In an electric field, it is the amount work to be done to move a unit charge (+1 Coulomb) from B to A. Electric potential difference is measured in V (Volts). In an electrical circuit, current flows from the higher potential to lower potential.

EMF (Electromotive Force)EMF is the electrical potential difference provided by an energy source like battery. Varying magnetic fields also can generate an EMF according to the Faraday’s law. Although EMF is also a voltage and measured in Volts (V), it is all about the generation of a potential difference.