Ans. If W is the work done in moving a unit positive charge q from infinity to a point in the field, the electric potential V at this point would be given by
where the work done W is equal to the energy supplied. When a charge is released in an electric field, It moves from a point of higher potential say A to a point at lower potential say B. If the potential of point A is Va and that of point B is Vb, the potential
energy of the charge at these points will be qVa and qVb respectively.
The change in potential energy of the charges when it moves from point A to B will be equal to qVa - qVb. This energy is utilized in doing some useful work. Thus
Energy supplied by the charge = q(Va - Vb)
If q is equal to one unit, then the potential difference between two points becomes equal to the energy supplied by the charge. Thus we define potential difference between two points as:
The energy supplied by a unit charge as it moves from one point to the other in the direction of the field.