Electrical Engineering ⇒ Topic : Voltage or Electric Potential

Energy is required to move a charge from one point to another. If W joules of energy is required for moving charge Q from point A to B, the voltage V between A and B is given by

where 1 volt = 1 joule/1 coulomb

In Figure (a), terminal A is +8 V above terminal B. In Figure (b), terminal B is -8 V above terminal A or in other words +8 V below A. Also it can be written as V_AB = +8 V [Figure (a)] and V_BA = -8 V [Figure(b)[ by using double subscript notation and in general V_AB = -V_BA .V_AB can be expressed as V_AB = V_A - V_B and V_AB means that voltage of A with respect to B.

According to the structure of an atom, we know that there are two types of charges: positive and negative. A force of attraction exists between these positive and negative charges. A certain amount of energy (work) is required to overcome the force and move the charges through a specific distance. All opposite charges possess a certain amount of potential energy because of the separation between them. The difference in potential energy of the charges is called the potential difference.
Potential difference in electrical terminology is known as voltage, and is denoted either by V or v. It is expressed in terms of energy (W) per unit charge (Q); i.e.

Just as we define electric field intensity as the force per unit charge, similarly electric potential is defined as the electric potential energy per unit charge.

       Consider an isolated charge +Q fixed in space . If a unit positive A + 1C charge (i. e. + 1C) is placed at infinity, the force charge on it due to charge +Q is *zero. If the unitat co charge at infinity is moved towards  +Q, a force of repulsion acts on it (like charges repel) and hence work is required to be done to bring it to a point like A. Hence when the unit positive charge is at A, it has some amount of electric potential energy which is a measure of electric potential. The closer the point to the charge, the higher will be the electric potential energy and hence the electric potential at that point. Therefore, electric potential at a point due to a charge depends upon the position of the point; being zero if the point is situated at infinity Obviously, in electric field, infinity is chosen as the point of **zero potential

  Hence electric potential at a point in an electric field is the amount of work done in bringing a unit positive charge (i.e. +1 C)from infinity to that point i.e.

where W is the work done to bring a charge of Q coulombs from infinity to the point under consideration.

Unit. The SI unit of electric potential is *volt and may be defined as under :The electric potential at a point in an electric field is 1 volt if 1 joule of work is done in bringing a unit positive charge (i.e. +1 C)from infinity to that point **against the electric field.

Thus when we say that potential at a point in an electric field is +5V, it simply means that 5 joules of work has been done in bringing a unit positive charge from infinity to that point

Electric Potential

When a body is charged, work is done in charging it. This work done is stored in the body in the form of potential energy. The charged body has the capacity to do work by moving other charges either by attraction or repulsion. The ability of the charged body to do work is called electric potential.

The capacity of a charged body to do work is called its electric potential.The greater the capacity of a charged body to do work, the greater is its electric potential.Obviously, the work done to charge a body to 1 coulomb will be a measure of its electric potential

The work done is measured in joules and charge in coulombs. Therefore, the unit of electric potential will be joules/ coulomb or volt. If W = 1 joule, Q= 1 coulomb, then V= 1/1 = 1 volt.

Hence a body is said to have an electric potential of 1 volt if 1 joule of work is done to give it a charge of 1 coulomb.

Thus, when we say that a body has an electric potential of 5 volts, it means that 5 joules of work has been done to charge the body to 1 coulomb. In other words, every coulomb of charge possesses an energy of 5 joules. The greater the joules/coulomb on a charged body, the greater is its electric potential.