Potential Difference: Potential difference between two terminal of a conductor is the work done while carrying unit positive charge from one terminal to the other terminal.
Unit of the potential difference is volt.
V = W / Q
or 1 V = 1JC-1
1 Volt is equal to 1 Jouls/coulomb.
and W = QV
Above equations should be memorized
Potential difference is measured by voltmeter.
If the VA and VB be the potential of the two end of a conductor then we can write
VA - VB = W /Q