*** State the working principle of Potentiometer explain with the help of circuit diagram How the e.m.f form two primary cells are compared by using Potentiometer.
Description :- A potentiometer consist of Manganin wire length 10 m arrange 10 parallel rows each one metre length on a wooden board.
It is used to compare the e.m.f of two given cells.
The potential difference between any two point along the uniform wire is directly proportional to it balancing length.
V = iR
V = i ( el/A )
V = ( ie/A )l
V =Φl
" V " directly proportional to " l "
= Potential drop , = specific resistance
Comparison of emfs of two cells :-
The primary circuit is consist of a cell of emf " E " Internal Resistance " r " connected in series to a key ( k1 ) and reheostart.
In the secondary circuit to cell whose emf E1 and E2 are compared are connected.
*** The cells in secondary circuit are connected through a two way key marked at the point 1,2 and 3.
*** Consider the key is connected between 1 and 3 so the galvanometer is connected to E1.
*** The position of the jockey is adjusted on the potentiometer wire the balance point is obtained l1.
" E1 " directly proportional to " l1"
E1=Φl1
= Potential drop
Now key is connected between 2 and 3 so the galvanometer is connected to E2. The position of jockey is adjusted on the potentiometer wire balance point is obtained l2.
" E2 " directly proportional to " l2 ".
E2 =Φ l2
From (1) & (2)
E1/E2 =Φl1/Φl2
E1/E2 = l1/l2
Principle Of Potentiometer :-
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