EMF vs Potential Difference
(electromotive force) are used to describe two different parameters between two points. 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 is a concept used in electric, magnetic and gravitational fields. 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 other words, gravitational potential difference between points A and B is the amount of work should be done to move a unit mass (1 kg) from point B to point A. In an electric field, it is the amount work to be done to move a unit charge (+1 Coulomb) from B to A. Gravitational potential difference is measured in J/kg where electric potential difference is measured in V (Volts). In an electrical circuit, current flows from the higher potential to lower potential.
However, in common use, the term ‘potential difference’ is mostly used to describe electrical potential differences. Therefore we have to use this term carefully to avoid misinterpretations.
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. An EMF is essential for an electric circuit to drive currents through the circuit. It act likes a charge pump.
When an electric circuit is run using an EMF, the sum of the potential drops in that circuit equals to the EMF according to the Kirchhoff’s second law. In addition to the batteries, which use electrochemical energies, solar cells, fuel cells and thermocouples are also examples for EMF generators.
What is the difference between Voltage and EMF?
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.