Electric Potential, Potential Difference & Difference between E.M.F. and Potential Difference

 1). 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 i.e

-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 10 volts, it means that 10 joules of work has been done to charge the body to 1 coulomb. In other words, every coulomb of charge possesses an energy of 10 joules. 

-The greater the joules/coulomb on a charged body, the greater is its electric potential.

2). Potential Difference-

-The difference in the potentials of two charged bodies is called potential difference.

-If two bodies have different electric potentials, a potential difference exists between the bodies. Consider two bodies A and B having potentials of 5 volts and 3 volts respectively as shown in Fig.1. 

-Each coulomb of charge on body A has an energy of 5 joules while each coulomb of charge on body B has an energy of 3 joules. Clearly, body A is at higher potential than the body B.

                        Fig 1                                        Fig 2

-If the two bodies are joined through a conductor [ Fig. 2], then electrons will flow from body B to body A. When the two bodies attain the same potential, the flow of current stops. 

-Therefore, we arrive at a very important conclusion that current will flow in a circuit if potential difference exists. 

-No potential difference, no current flow. 

-It may be noted that potential difference is sometimes called voltage. 

 Unit  -As the unit of electric potential is volt, one can expect that unit of potential difference will also be volt.

 -It is defined as under : The potential difference between two points is 1 volt if one joule of work is done or released in transferring 1 coulomb of charge from one point to the other.

3). Concept of E.M.F. and Potential Difference-

-There is a distinct difference between e.m.f. and potential difference. 

-The e.m.f. of a device, say a battery, is a measure of the energy the battery gives to each coulomb of charge. 

-Thus if a battery supplies 4 joules of energy per coulomb, we say that it has an e.m.f. of 4 volts. 

-The energy given to each coulomb in a battery is due to the chemical action. 

-The potential difference between two points, say A and B, is a measure of the energy used by one coulomb in moving from A to B. 

-Thus if potential difference between points A and B is 2 volts, it means that each coulomb will give up an energy of 2 joules in moving from A to B.

NOTE-

Electromotive force (e.m.f.) maintains potential difference while potential difference causes current to flow.