The potential difference is expressed in volt (V). The potential difference between two points is said to be 1 volt if the work is done in moving 1-coulomb charge from one point to other is 1 joule. 1 volt= 1 joule/ 1 coulomb Unit for measuring the potential difference is volt and instrument used for measuring potential difference is a voltmeter.
Its potential is taken as zero potential. Thus the positively charged conductor has more positive potential than the earth. A negatively charged conductor has negative potential less than that of the earth. The electric potential difference between two points in an electric circuit is the work done in moving a unit positive charge from one point to the other.