Electrical Engineering ⇒ Topic : Unit of resistance

Seema
 
Unit of resistance. The practical unit of resistance is ohm and is represented by the symbol Q. It is defined as under : A wire is said to have a resistance of 1 ohm if a p.d. of I volt across its ends causes 1 ampere to flow through it See Fig. (a).
figure (a) There is another way of defining ohm. A wire is said to have a resistance of 1 ohm if it releases ]joule (or develops 0.24 calorie of heat) when a current of I A flows through it for I second. A little reflection shows that second definition leads to the first definition. Thus 1 A current flowing for 1 second means that total charge flowing is Q=/x t=1 x 1=1 coulomb. Now the charge flowing between A and B (See Fig. 1.10) is 1 coulomb and energy released is 1 joule (or 0.24 calorie). Obviously, by definition, p.d. between A and B should be 1 volt  
 
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