Electric Potential – Just like an electric field a charge is also surrounded by a field of electric potential. The potential at any point in the field is defined as the potential energy of a unit positive charge placed at that point which is equal to the amount of work done in bringing a unit positive charge from infinity to that point.
If W is the amount of work done in bringing a test charge +q from infinity to a certain point in the field, the potential V at this point would be given by
Potential is a scalar quantity. Its SI unit is known as volt. If the potential energy of one coulomb positive charge at a point is one joule, the potential of that point would be one volt.
When we release a body in a gravitational field, it moves from a point of higher potential energy to a point of lower potential energy. Similarly when a charge q is left for free motion in an electric field, it moves from a point of higher potential say A to a point of lower potential say B. if the potential of the point A is VA and that of B is VB, the potential energy of the charge at these points would be qVa and qVB respectively. The difference of these potential energies qVA – qVB is supplied by the charge as it moves from A to B, this energy can be utilize d by us in doing different kinds of work. Thus, we have the following expression for the energy supplied by a charge:
E =q (VA – VB) ………… (15.7)
If q is equal to one unit, then the potential difference between two points gets equal to the energy supplied by the charge. Thus, the potential difference between two points can be defined as the energy supplied by a unit charge as it moves from one point to the other.
If a positive charge is transferred from a point of lower potential to a point of higher potential, energy would have to be supplied to it.
When we release a negative charge in an electric field, its behavior is just the opposite. It supplies us energy by moving freely from a point of lower potential to a point of higher potential. If we move a negative charge from higher to lower potential we will have to supply energy to the charge by doing work on it.
We can define a new unit of energy known as electron volt (ev) by noting the fact that the product of charge and potential difference is energy. It is equal to the amount of energy supplied by an electron as it moves between two points having a potential difference of one volt. In Eq. 15.7
This is a small unit of energy and is often used in atomic and nuclear physics.
Do you know?
In 1776, an Italian scientist Alexndro Volta invented the chemical battery. Volt, the unit of potential difference has been named after him.