Electrical Engineering ⇒ Topic : Concept of E.M.F. and Potential Difference

Seema
 
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. Illustration :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.Illustration. The difference between e.m.f. and p.d. can be made more illustrative by refening to Fig.(a) Here battery has an e.m.f. of 4 volts. It means battery supplies 4 joules of energy to each coulomb continuously. As each coulomb travels from the positive terminal of the battery, it gives up its most of 1 energy to resistances (2 Q and 2 Q in this case) and remaining to connecting wires. When it returns to the negative terminal, it has lost all its energy originally supplied by the battery. The battery now supplies fresh energy to each coulomb (4 joules in the present case) to start the journey once again.
figure (a) The p.d. between any two points in the circuit is the energy used by one coulomb in moving from one point to another. Thus in Fig.(a), p.d. betweenA and B is 2 volts. It means that 1 coulomb will give up an energy of 2 joules in moving from A to B. This energy will be released as heat from the part AB of the circuit. The following points may be noted carefully
 
 
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