Write the difference between potential difference and emf.

Hint: Potential difference is the measure of energy between any two points in the circuit and electromotive force is the maximum voltage across the terminals of a battery when no current is flowing.

Complete step by step answer:
Potential difference is the voltage across the terminals of the battery while electro motive force is the potential difference between the terminals of a battery when no current is flowing through an external circuit and when the circuit is open.
Both of them are measured in the unit volts(V), electromotive force is denoted by the symbol 'E' and potential difference is denoted by the symbol 'V'.
Formula for calculating potential difference:
${\text{V = IR}}$
where ${\text{V}}$ is the potential difference, ${\text{I}}$ is current and ${\text{R}}$ is resistance.
There are two main formulas for calculating electromotive force i.e.:
First formula is:
${\text{E = }}\dfrac{{\text{W}}}{Q}$
where ${\text{E}}$ is the electromotive force, ${\text{W}}$ is work done in taking a unit charge and ${\text{Q}}$ is the charge of the circuit.
Second formula is:
$
  {\text{E = V + IR}} \\
  {\text{E = I}}\left( {{\text{r + R}}} \right) \\
$
where ${\text{E}}$ is electromotive force, ${\text{V}}$ is potential difference, ${\text{I}}$ is current, ${\text{R}}$ is load resistance and $r$ is internal resistance.
Potential difference is directly dependent on the resistance between the two points while electromotive force does not depend on the circuit resistance.
Electromotive force is also present when no current is drawn through the battery while in the absence of current potential difference across the conductor is zero also electro motive force basically transmits current both inside and outside of the cell and potential difference transfers the current between two points in the cell.

Note:One thing is to be noted that electromotive forces occur in the presence of electric field, magnetic field and also in gravitational field while potential difference induces only in electric field.