Define Electromotive force (emf) and potential difference.

Hint: To compare emf and potential difference we study their definitions and their respective properties to identify some key differences, i.e how are they originated, how they behave in similar conditions, their units of measurement and if one occurs as a result of the other etc.

Complete step by step answer:
Emf or the electromotive force is the energy that is given to a unit charge by a source like a battery etc.
Whereas, potential difference is the difference in potential between two points.
Electromotive force is a concept that is attributed to the entire circuit whereas the potential difference is with respect to any two given points.
Electromotive force only depends on the source, it does not depend on the resistance of the circuit, whereas the potential difference is directly proportional to the resistance.
The value of emf of a circuit does not change and it is greater than the value of potential difference, whereas the value of potential difference changes and it becomes equal to emf when the circuit is fully charged.
Emf is the force that causes electrons to flow in a circuit, while potential difference arises in a circuit due to its emf.
Emf is measured by an emf meter, it is denoted by ε while potential difference is measured by a voltmeter and is denoted by V.
If the current flowing in a circuit is zero, emf exists but potential difference does not exist.

Note:
In order to answer this type of question the key is to know that potential difference is a consequence of having an emf in an electric circuit but not vice versa. Both the attributes are measured in the units “Volts” represented as ‘V’. In other words it can be said that electrons flow from one point to another because there exists a potential difference between them. Michael Faraday is credited with the discovery of emf and potential difference is discovered by Alessandro Volta, both physicists.