What is the difference between emf and voltage?

Potential difference is simply a voltage difference between two points in a closed electrical circuit with a voltage source circuit (or in free space). So, the interesting fact is the potential difference can be a source of emf if it is used to move charges. The term ‘potential difference’ is a general term and found in all the energy fields such as electric, magnetic and gravitational fields. But emf is only pertaining to electrical circuits. Although, both ‘electrical potential difference’ and emf are measured in Volts (V), there are many differences between them.

Potential Difference
Potential 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.

So the important differences between Voltage and EMF is:

1. The term ‘potential difference’ is used in all energy fields (electric, magnetic, gravitational), and ‘EMF’ is only used in electric circuits.

2. EMF is the electrical potential difference generated by a source like battery or generator.

3. We can measure potential difference between any two points, but EMF exists only between the two ends of a source.

4. Sum of ‘potential drops’ around a circuit is equal to total EMF according to Kirchhoff’s second law.